ext4: fix NULL pointer dereference in ext4_mark_inode_dirty()

[linux/fpc-iii.git] / fs / ext4 / inode.c

/*
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *      (jj@sunsite.ms.mff.cuni.cz)
 *
 *  Assorted race fixes, rewrite of ext4_get_block() by Al Viro, 2000
 */

#include <linux/fs.h>
#include <linux/time.h>
#include <linux/jbd2.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/mpage.h>
#include <linux/namei.h>
#include <linux/uio.h>
#include <linux/bio.h>
#include <linux/workqueue.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include <linux/aio.h>
#include <linux/bitops.h>

#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "truncate.h"

#include <trace/events/ext4.h>

#define MPAGE_DA_EXTENT_TAIL 0x01

static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
                              struct ext4_inode_info *ei)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        __u16 csum_lo;
        __u16 csum_hi = 0;
        __u32 csum;

        csum_lo = le16_to_cpu(raw->i_checksum_lo);
        raw->i_checksum_lo = 0;
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi)) {
                csum_hi = le16_to_cpu(raw->i_checksum_hi);
                raw->i_checksum_hi = 0;
        }

        csum = ext4_chksum(sbi, ei->i_csum_seed, (__u8 *)raw,
                           EXT4_INODE_SIZE(inode->i_sb));

        raw->i_checksum_lo = cpu_to_le16(csum_lo);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                raw->i_checksum_hi = cpu_to_le16(csum_hi);

        return csum;
}

static int ext4_inode_csum_verify(struct inode *inode, struct ext4_inode *raw,
                                  struct ext4_inode_info *ei)
{
        __u32 provided, calculated;

        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_LINUX) ||
            !ext4_has_metadata_csum(inode->i_sb))
                return 1;

        provided = le16_to_cpu(raw->i_checksum_lo);
        calculated = ext4_inode_csum(inode, raw, ei);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                provided |= ((__u32)le16_to_cpu(raw->i_checksum_hi)) << 16;
        else
                calculated &= 0xFFFF;

        return provided == calculated;
}

static void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw,
                                struct ext4_inode_info *ei)
{
        __u32 csum;

        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_LINUX) ||
            !ext4_has_metadata_csum(inode->i_sb))
                return;

        csum = ext4_inode_csum(inode, raw, ei);
        raw->i_checksum_lo = cpu_to_le16(csum & 0xFFFF);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE &&
            EXT4_FITS_IN_INODE(raw, ei, i_checksum_hi))
                raw->i_checksum_hi = cpu_to_le16(csum >> 16);
}

static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                              loff_t new_size)
{
        trace_ext4_begin_ordered_truncate(inode, new_size);
        /*
         * If jinode is zero, then we never opened the file for
         * writing, so there's no need to call
         * jbd2_journal_begin_ordered_truncate() since there's no
         * outstanding writes we need to flush.
         */
        if (!EXT4_I(inode)->jinode)
                return 0;
        return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
                                                   EXT4_I(inode)->jinode,
                                                   new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned int offset,
                                unsigned int length);
static int __ext4_journalled_writepage(struct page *page, unsigned int len);
static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh);
static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
                                  int pextents);

/*
 * Test whether an inode is a fast symlink.
 */
static int ext4_inode_is_fast_symlink(struct inode *inode)
{
        int ea_blocks = EXT4_I(inode)->i_file_acl ?
                EXT4_CLUSTER_SIZE(inode->i_sb) >> 9 : 0;

        if (ext4_has_inline_data(inode))
                return 0;

        return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
}

/*
 * Restart the transaction associated with *handle.  This does a commit,
 * so before we call here everything must be consistently dirtied against
 * this transaction.
 */
int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
                                 int nblocks)
{
        int ret;

        /*
         * Drop i_data_sem to avoid deadlock with ext4_map_blocks.  At this
         * moment, get_block can be called only for blocks inside i_size since
         * page cache has been already dropped and writes are blocked by
         * i_mutex. So we can safely drop the i_data_sem here.
         */
        BUG_ON(EXT4_JOURNAL(inode) == NULL);
        jbd_debug(2, "restarting handle %p\n", handle);
        up_write(&EXT4_I(inode)->i_data_sem);
        ret = ext4_journal_restart(handle, nblocks);
        down_write(&EXT4_I(inode)->i_data_sem);
        ext4_discard_preallocations(inode);

        return ret;
}

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext4_evict_inode(struct inode *inode)
{
        handle_t *handle;
        int err;

        trace_ext4_evict_inode(inode);

        if (inode->i_nlink) {
                /*
                 * When journalling data dirty buffers are tracked only in the
                 * journal. So although mm thinks everything is clean and
                 * ready for reaping the inode might still have some pages to
                 * write in the running transaction or waiting to be
                 * checkpointed. Thus calling jbd2_journal_invalidatepage()
                 * (via truncate_inode_pages()) to discard these buffers can
                 * cause data loss. Also even if we did not discard these
                 * buffers, we would have no way to find them after the inode
                 * is reaped and thus user could see stale data if he tries to
                 * read them before the transaction is checkpointed. So be
                 * careful and force everything to disk here... We use
                 * ei->i_datasync_tid to store the newest transaction
                 * containing inode's data.
                 *
                 * Note that directories do not have this problem because they
                 * don't use page cache.
                 */
                if (ext4_should_journal_data(inode) &&
                    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode)) &&
                    inode->i_ino != EXT4_JOURNAL_INO) {
                        journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
                        tid_t commit_tid = EXT4_I(inode)->i_datasync_tid;

                        jbd2_complete_transaction(journal, commit_tid);
                        filemap_write_and_wait(&inode->i_data);
                }
                truncate_inode_pages_final(&inode->i_data);

                WARN_ON(atomic_read(&EXT4_I(inode)->i_ioend_count));
                goto no_delete;
        }

        if (is_bad_inode(inode))
                goto no_delete;
        dquot_initialize(inode);

        if (ext4_should_order_data(inode))
                ext4_begin_ordered_truncate(inode, 0);
        truncate_inode_pages_final(&inode->i_data);

        WARN_ON(atomic_read(&EXT4_I(inode)->i_ioend_count));

        /*
         * Protect us against freezing - iput() caller didn't have to have any
         * protection against it
         */
        sb_start_intwrite(inode->i_sb);
        handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE,
                                    ext4_blocks_for_truncate(inode)+3);
        if (IS_ERR(handle)) {
                ext4_std_error(inode->i_sb, PTR_ERR(handle));
                /*
                 * If we're going to skip the normal cleanup, we still need to
                 * make sure that the in-core orphan linked list is properly
                 * cleaned up.
                 */
                ext4_orphan_del(NULL, inode);
                sb_end_intwrite(inode->i_sb);
                goto no_delete;
        }

        if (IS_SYNC(inode))
                ext4_handle_sync(handle);
        inode->i_size = 0;
        err = ext4_mark_inode_dirty(handle, inode);
        if (err) {
                ext4_warning(inode->i_sb,
                             "couldn't mark inode dirty (err %d)", err);
                goto stop_handle;
        }
        if (inode->i_blocks)
                ext4_truncate(inode);

        /*
         * ext4_ext_truncate() doesn't reserve any slop when it
         * restarts journal transactions; therefore there may not be
         * enough credits left in the handle to remove the inode from
         * the orphan list and set the dtime field.
         */
        if (!ext4_handle_has_enough_credits(handle, 3)) {
                err = ext4_journal_extend(handle, 3);
                if (err > 0)
                        err = ext4_journal_restart(handle, 3);
                if (err != 0) {
                        ext4_warning(inode->i_sb,
                                     "couldn't extend journal (err %d)", err);
                stop_handle:
                        ext4_journal_stop(handle);
                        ext4_orphan_del(NULL, inode);
                        sb_end_intwrite(inode->i_sb);
                        goto no_delete;
                }
        }

        /*
         * Kill off the orphan record which ext4_truncate created.
         * AKPM: I think this can be inside the above `if'.
         * Note that ext4_orphan_del() has to be able to cope with the
         * deletion of a non-existent orphan - this is because we don't
         * know if ext4_truncate() actually created an orphan record.
         * (Well, we could do this if we need to, but heck - it works)
         */
        ext4_orphan_del(handle, inode);
        EXT4_I(inode)->i_dtime  = get_seconds();

        /*
         * One subtle ordering requirement: if anything has gone wrong
         * (transaction abort, IO errors, whatever), then we can still
         * do these next steps (the fs will already have been marked as
         * having errors), but we can't free the inode if the mark_dirty
         * fails.
         */
        if (ext4_mark_inode_dirty(handle, inode))
                /* If that failed, just do the required in-core inode clear. */
                ext4_clear_inode(inode);
        else
                ext4_free_inode(handle, inode);
        ext4_journal_stop(handle);
        sb_end_intwrite(inode->i_sb);
        return;
no_delete:
        ext4_clear_inode(inode);        /* We must guarantee clearing of inode... */
}

#ifdef CONFIG_QUOTA
qsize_t *ext4_get_reserved_space(struct inode *inode)
{
        return &EXT4_I(inode)->i_reserved_quota;
}
#endif

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate a block located at @lblock
 */
static int ext4_calc_metadata_amount(struct inode *inode, ext4_lblk_t lblock)
{
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                return ext4_ext_calc_metadata_amount(inode, lblock);

        return ext4_ind_calc_metadata_amount(inode, lblock);
}

/*
 * Called with i_data_sem down, which is important since we can call
 * ext4_discard_preallocations() from here.
 */
void ext4_da_update_reserve_space(struct inode *inode,
                                        int used, int quota_claim)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);

        spin_lock(&ei->i_block_reservation_lock);
        trace_ext4_da_update_reserve_space(inode, used, quota_claim);
        if (unlikely(used > ei->i_reserved_data_blocks)) {
                ext4_warning(inode->i_sb, "%s: ino %lu, used %d "
                         "with only %d reserved data blocks",
                         __func__, inode->i_ino, used,
                         ei->i_reserved_data_blocks);
                WARN_ON(1);
                used = ei->i_reserved_data_blocks;
        }

        if (unlikely(ei->i_allocated_meta_blocks > ei->i_reserved_meta_blocks)) {
                ext4_warning(inode->i_sb, "ino %lu, allocated %d "
                        "with only %d reserved metadata blocks "
                        "(releasing %d blocks with reserved %d data blocks)",
                        inode->i_ino, ei->i_allocated_meta_blocks,
                             ei->i_reserved_meta_blocks, used,
                             ei->i_reserved_data_blocks);
                WARN_ON(1);
                ei->i_allocated_meta_blocks = ei->i_reserved_meta_blocks;
        }

        /* Update per-inode reservations */
        ei->i_reserved_data_blocks -= used;
        ei->i_reserved_meta_blocks -= ei->i_allocated_meta_blocks;
        percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                           used + ei->i_allocated_meta_blocks);
        ei->i_allocated_meta_blocks = 0;

        if (ei->i_reserved_data_blocks == 0) {
                /*
                 * We can release all of the reserved metadata blocks
                 * only when we have written all of the delayed
                 * allocation blocks.
                 */
                percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                                   ei->i_reserved_meta_blocks);
                ei->i_reserved_meta_blocks = 0;
                ei->i_da_metadata_calc_len = 0;
        }
        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

        /* Update quota subsystem for data blocks */
        if (quota_claim)
                dquot_claim_block(inode, EXT4_C2B(sbi, used));
        else {
                /*
                 * We did fallocate with an offset that is already delayed
                 * allocated. So on delayed allocated writeback we should
                 * not re-claim the quota for fallocated blocks.
                 */
                dquot_release_reservation_block(inode, EXT4_C2B(sbi, used));
        }

        /*
         * If we have done all the pending block allocations and if
         * there aren't any writers on the inode, we can discard the
         * inode's preallocations.
         */
        if ((ei->i_reserved_data_blocks == 0) &&
            (atomic_read(&inode->i_writecount) == 0))
                ext4_discard_preallocations(inode);
}

static int __check_block_validity(struct inode *inode, const char *func,
                                unsigned int line,
                                struct ext4_map_blocks *map)
{
        if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), map->m_pblk,
                                   map->m_len)) {
                ext4_error_inode(inode, func, line, map->m_pblk,
                                 "lblock %lu mapped to illegal pblock "
                                 "(length %d)", (unsigned long) map->m_lblk,
                                 map->m_len);
                return -EIO;
        }
        return 0;
}

#define check_block_validity(inode, map)        \
        __check_block_validity((inode), __func__, __LINE__, (map))

#ifdef ES_AGGRESSIVE_TEST
static void ext4_map_blocks_es_recheck(handle_t *handle,
                                       struct inode *inode,
                                       struct ext4_map_blocks *es_map,
                                       struct ext4_map_blocks *map,
                                       int flags)
{
        int retval;

        map->m_flags = 0;
        /*
         * There is a race window that the result is not the same.
         * e.g. xfstests #223 when dioread_nolock enables.  The reason
         * is that we lookup a block mapping in extent status tree with
         * out taking i_data_sem.  So at the time the unwritten extent
         * could be converted.
         */
        if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
                down_read(&EXT4_I(inode)->i_data_sem);
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        }
        if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
                up_read((&EXT4_I(inode)->i_data_sem));
        /*
         * Clear EXT4_MAP_FROM_CLUSTER and EXT4_MAP_BOUNDARY flag
         * because it shouldn't be marked in es_map->m_flags.
         */
        map->m_flags &= ~(EXT4_MAP_FROM_CLUSTER | EXT4_MAP_BOUNDARY);

        /*
         * We don't check m_len because extent will be collpased in status
         * tree.  So the m_len might not equal.
         */
        if (es_map->m_lblk != map->m_lblk ||
            es_map->m_flags != map->m_flags ||
            es_map->m_pblk != map->m_pblk) {
                printk("ES cache assertion failed for inode: %lu "
                       "es_cached ex [%d/%d/%llu/%x] != "
                       "found ex [%d/%d/%llu/%x] retval %d flags %x\n",
                       inode->i_ino, es_map->m_lblk, es_map->m_len,
                       es_map->m_pblk, es_map->m_flags, map->m_lblk,
                       map->m_len, map->m_pblk, map->m_flags,
                       retval, flags);
        }
}
#endif /* ES_AGGRESSIVE_TEST */

/*
 * The ext4_map_blocks() function tries to look up the requested blocks,
 * and returns if the blocks are already mapped.
 *
 * Otherwise it takes the write lock of the i_data_sem and allocate blocks
 * and store the allocated blocks in the result buffer head and mark it
 * mapped.
 *
 * If file type is extents based, it will call ext4_ext_map_blocks(),
 * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
 * based files
 *
 * On success, it returns the number of blocks being mapped or allocated.
 * if create==0 and the blocks are pre-allocated and unwritten block,
 * the result buffer head is unmapped. If the create ==1, it will make sure
 * the buffer head is mapped.
 *
 * It returns 0 if plain look up failed (blocks have not been allocated), in
 * that case, buffer head is unmapped
 *
 * It returns the error in case of allocation failure.
 */
int ext4_map_blocks(handle_t *handle, struct inode *inode,
                    struct ext4_map_blocks *map, int flags)
{
        struct extent_status es;
        int retval;
        int ret = 0;
#ifdef ES_AGGRESSIVE_TEST
        struct ext4_map_blocks orig_map;

        memcpy(&orig_map, map, sizeof(*map));
#endif

        map->m_flags = 0;
        ext_debug("ext4_map_blocks(): inode %lu, flag %d, max_blocks %u,"
                  "logical block %lu\n", inode->i_ino, flags, map->m_len,
                  (unsigned long) map->m_lblk);

        /*
         * ext4_map_blocks returns an int, and m_len is an unsigned int
         */
        if (unlikely(map->m_len > INT_MAX))
                map->m_len = INT_MAX;

        /* We can handle the block number less than EXT_MAX_BLOCKS */
        if (unlikely(map->m_lblk >= EXT_MAX_BLOCKS))
                return -EIO;

        /* Lookup extent status tree firstly */
        if (ext4_es_lookup_extent(inode, map->m_lblk, &es)) {
                ext4_es_lru_add(inode);
                if (ext4_es_is_written(&es) || ext4_es_is_unwritten(&es)) {
                        map->m_pblk = ext4_es_pblock(&es) +
                                        map->m_lblk - es.es_lblk;
                        map->m_flags |= ext4_es_is_written(&es) ?
                                        EXT4_MAP_MAPPED : EXT4_MAP_UNWRITTEN;
                        retval = es.es_len - (map->m_lblk - es.es_lblk);
                        if (retval > map->m_len)
                                retval = map->m_len;
                        map->m_len = retval;
                } else if (ext4_es_is_delayed(&es) || ext4_es_is_hole(&es)) {
                        retval = 0;
                } else {
                        BUG_ON(1);
                }
#ifdef ES_AGGRESSIVE_TEST
                ext4_map_blocks_es_recheck(handle, inode, map,
                                           &orig_map, flags);
#endif
                goto found;
        }

        /*
         * Try to see if we can get the block without requesting a new
         * file system block.
         */
        if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
                down_read(&EXT4_I(inode)->i_data_sem);
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags &
                                             EXT4_GET_BLOCKS_KEEP_SIZE);
        }
        if (retval > 0) {
                unsigned int status;

                if (unlikely(retval != map->m_len)) {
                        ext4_warning(inode->i_sb,
                                     "ES len assertion failed for inode "
                                     "%lu: retval %d != map->m_len %d",
                                     inode->i_ino, retval, map->m_len);
                        WARN_ON(1);
                }

                status = map->m_flags & EXT4_MAP_UNWRITTEN ?
                                EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
                if (!(flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) &&
                    !(status & EXTENT_STATUS_WRITTEN) &&
                    ext4_find_delalloc_range(inode, map->m_lblk,
                                             map->m_lblk + map->m_len - 1))
                        status |= EXTENT_STATUS_DELAYED;
                ret = ext4_es_insert_extent(inode, map->m_lblk,
                                            map->m_len, map->m_pblk, status);
                if (ret < 0)
                        retval = ret;
        }
        if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
                up_read((&EXT4_I(inode)->i_data_sem));

found:
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                ret = check_block_validity(inode, map);
                if (ret != 0)
                        return ret;
        }

        /* If it is only a block(s) look up */
        if ((flags & EXT4_GET_BLOCKS_CREATE) == 0)
                return retval;

        /*
         * Returns if the blocks have already allocated
         *
         * Note that if blocks have been preallocated
         * ext4_ext_get_block() returns the create = 0
         * with buffer head unmapped.
         */
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED)
                /*
                 * If we need to convert extent to unwritten
                 * we continue and do the actual work in
                 * ext4_ext_map_blocks()
                 */
                if (!(flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN))
                        return retval;

        /*
         * Here we clear m_flags because after allocating an new extent,
         * it will be set again.
         */
        map->m_flags &= ~EXT4_MAP_FLAGS;

        /*
         * New blocks allocate and/or writing to unwritten extent
         * will possibly result in updating i_data, so we take
         * the write lock of i_data_sem, and call get_blocks()
         * with create == 1 flag.
         */
        down_write(&EXT4_I(inode)->i_data_sem);

        /*
         * if the caller is from delayed allocation writeout path
         * we have already reserved fs blocks for allocation
         * let the underlying get_block() function know to
         * avoid double accounting
         */
        if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
                ext4_set_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);
        /*
         * We need to check for EXT4 here because migrate
         * could have changed the inode type in between
         */
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                retval = ext4_ext_map_blocks(handle, inode, map, flags);
        } else {
                retval = ext4_ind_map_blocks(handle, inode, map, flags);

                if (retval > 0 && map->m_flags & EXT4_MAP_NEW) {
                        /*
                         * We allocated new blocks which will result in
                         * i_data's format changing.  Force the migrate
                         * to fail by clearing migrate flags
                         */
                        ext4_clear_inode_state(inode, EXT4_STATE_EXT_MIGRATE);
                }

                /*
                 * Update reserved blocks/metadata blocks after successful
                 * block allocation which had been deferred till now. We don't
                 * support fallocate for non extent files. So we can update
                 * reserve space here.
                 */
                if ((retval > 0) &&
                        (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE))
                        ext4_da_update_reserve_space(inode, retval, 1);
        }
        if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
                ext4_clear_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);

        if (retval > 0) {
                unsigned int status;

                if (unlikely(retval != map->m_len)) {
                        ext4_warning(inode->i_sb,
                                     "ES len assertion failed for inode "
                                     "%lu: retval %d != map->m_len %d",
                                     inode->i_ino, retval, map->m_len);
                        WARN_ON(1);
                }

                /*
                 * If the extent has been zeroed out, we don't need to update
                 * extent status tree.
                 */
                if ((flags & EXT4_GET_BLOCKS_PRE_IO) &&
                    ext4_es_lookup_extent(inode, map->m_lblk, &es)) {
                        if (ext4_es_is_written(&es))
                                goto has_zeroout;
                }
                status = map->m_flags & EXT4_MAP_UNWRITTEN ?
                                EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
                if (!(flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) &&
                    !(status & EXTENT_STATUS_WRITTEN) &&
                    ext4_find_delalloc_range(inode, map->m_lblk,
                                             map->m_lblk + map->m_len - 1))
                        status |= EXTENT_STATUS_DELAYED;
                ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
                                            map->m_pblk, status);
                if (ret < 0)
                        retval = ret;
        }

has_zeroout:
        up_write((&EXT4_I(inode)->i_data_sem));
        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                ret = check_block_validity(inode, map);
                if (ret != 0)
                        return ret;
        }
        return retval;
}

/*
 * Update EXT4_MAP_FLAGS in bh->b_state. For buffer heads attached to pages
 * we have to be careful as someone else may be manipulating b_state as well.
 */
static void ext4_update_bh_state(struct buffer_head *bh, unsigned long flags)
{
        unsigned long old_state;
        unsigned long new_state;

        flags &= EXT4_MAP_FLAGS;

        /* Dummy buffer_head? Set non-atomically. */
        if (!bh->b_page) {
                bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | flags;
                return;
        }
        /*
         * Someone else may be modifying b_state. Be careful! This is ugly but
         * once we get rid of using bh as a container for mapping information
         * to pass to / from get_block functions, this can go away.
         */
        do {
                old_state = ACCESS_ONCE(bh->b_state);
                new_state = (old_state & ~EXT4_MAP_FLAGS) | flags;
        } while (unlikely(
                 cmpxchg(&bh->b_state, old_state, new_state) != old_state));
}

/* Maximum number of blocks we map for direct IO at once. */
#define DIO_MAX_BLOCKS 4096

static int _ext4_get_block(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh, int flags)
{
        handle_t *handle = ext4_journal_current_handle();
        struct ext4_map_blocks map;
        int ret = 0, started = 0;
        int dio_credits;

        if (ext4_has_inline_data(inode))
                return -ERANGE;

        map.m_lblk = iblock;
        map.m_len = bh->b_size >> inode->i_blkbits;

        if (flags && !(flags & EXT4_GET_BLOCKS_NO_LOCK) && !handle) {
                /* Direct IO write... */
                if (map.m_len > DIO_MAX_BLOCKS)
                        map.m_len = DIO_MAX_BLOCKS;
                dio_credits = ext4_chunk_trans_blocks(inode, map.m_len);
                handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS,
                                            dio_credits);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        return ret;
                }
                started = 1;
        }

        ret = ext4_map_blocks(handle, inode, &map, flags);
        if (ret > 0) {
                ext4_io_end_t *io_end = ext4_inode_aio(inode);

                map_bh(bh, inode->i_sb, map.m_pblk);
                ext4_update_bh_state(bh, map.m_flags);
                if (io_end && io_end->flag & EXT4_IO_END_UNWRITTEN)
                        set_buffer_defer_completion(bh);
                bh->b_size = inode->i_sb->s_blocksize * map.m_len;
                ret = 0;
        }
        if (started)
                ext4_journal_stop(handle);
        return ret;
}

int ext4_get_block(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh, int create)
{
        return _ext4_get_block(inode, iblock, bh,
                               create ? EXT4_GET_BLOCKS_CREATE : 0);
}

/*
 * `handle' can be NULL if create is zero
 */
struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
                                ext4_lblk_t block, int create, int *errp)
{
        struct ext4_map_blocks map;
        struct buffer_head *bh;
        int fatal = 0, err;

        J_ASSERT(handle != NULL || create == 0);

        map.m_lblk = block;
        map.m_len = 1;
        err = ext4_map_blocks(handle, inode, &map,
                              create ? EXT4_GET_BLOCKS_CREATE : 0);

        /* ensure we send some value back into *errp */
        *errp = 0;

        if (create && err == 0)
                err = -ENOSPC;  /* should never happen */
        if (err < 0)
                *errp = err;
        if (err <= 0)
                return NULL;

        bh = sb_getblk(inode->i_sb, map.m_pblk);
        if (unlikely(!bh)) {
                *errp = -ENOMEM;
                return NULL;
        }
        if (map.m_flags & EXT4_MAP_NEW) {
                J_ASSERT(create != 0);
                J_ASSERT(handle != NULL);

                /*
                 * Now that we do not always journal data, we should
                 * keep in mind whether this should always journal the
                 * new buffer as metadata.  For now, regular file
                 * writes use ext4_get_block instead, so it's not a
                 * problem.
                 */
                lock_buffer(bh);
                BUFFER_TRACE(bh, "call get_create_access");
                fatal = ext4_journal_get_create_access(handle, bh);
                if (!fatal && !buffer_uptodate(bh)) {
                        memset(bh->b_data, 0, inode->i_sb->s_blocksize);
                        set_buffer_uptodate(bh);
                }
                unlock_buffer(bh);
                BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, inode, bh);
                if (!fatal)
                        fatal = err;
        } else {
                BUFFER_TRACE(bh, "not a new buffer");
        }
        if (fatal) {
                *errp = fatal;
                brelse(bh);
                bh = NULL;
        }
        return bh;
}

struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
                               ext4_lblk_t block, int create, int *err)
{
        struct buffer_head *bh;

        bh = ext4_getblk(handle, inode, block, create, err);
        if (!bh)
                return bh;
        if (buffer_uptodate(bh))
                return bh;
        ll_rw_block(READ | REQ_META | REQ_PRIO, 1, &bh);
        wait_on_buffer(bh);
        if (buffer_uptodate(bh))
                return bh;
        put_bh(bh);
        *err = -EIO;
        return NULL;
}

int ext4_walk_page_buffers(handle_t *handle,
                           struct buffer_head *head,
                           unsigned from,
                           unsigned to,
                           int *partial,
                           int (*fn)(handle_t *handle,
                                     struct buffer_head *bh))
{
        struct buffer_head *bh;
        unsigned block_start, block_end;
        unsigned blocksize = head->b_size;
        int err, ret = 0;
        struct buffer_head *next;

        for (bh = head, block_start = 0;
             ret == 0 && (bh != head || !block_start);
             block_start = block_end, bh = next) {
                next = bh->b_this_page;
                block_end = block_start + blocksize;
                if (block_end <= from || block_start >= to) {
                        if (partial && !buffer_uptodate(bh))
                                *partial = 1;
                        continue;
                }
                err = (*fn)(handle, bh);
                if (!ret)
                        ret = err;
        }
        return ret;
}

/*
 * To preserve ordering, it is essential that the hole instantiation and
 * the data write be encapsulated in a single transaction.  We cannot
 * close off a transaction and start a new one between the ext4_get_block()
 * and the commit_write().  So doing the jbd2_journal_start at the start of
 * prepare_write() is the right place.
 *
 * Also, this function can nest inside ext4_writepage().  In that case, we
 * *know* that ext4_writepage() has generated enough buffer credits to do the
 * whole page.  So we won't block on the journal in that case, which is good,
 * because the caller may be PF_MEMALLOC.
 *
 * By accident, ext4 can be reentered when a transaction is open via
 * quota file writes.  If we were to commit the transaction while thus
 * reentered, there can be a deadlock - we would be holding a quota
 * lock, and the commit would never complete if another thread had a
 * transaction open and was blocking on the quota lock - a ranking
 * violation.
 *
 * So what we do is to rely on the fact that jbd2_journal_stop/journal_start
 * will _not_ run commit under these circumstances because handle->h_ref
 * is elevated.  We'll still have enough credits for the tiny quotafile
 * write.
 */
int do_journal_get_write_access(handle_t *handle,
                                struct buffer_head *bh)
{
        int dirty = buffer_dirty(bh);
        int ret;

        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        /*
         * __block_write_begin() could have dirtied some buffers. Clean
         * the dirty bit as jbd2_journal_get_write_access() could complain
         * otherwise about fs integrity issues. Setting of the dirty bit
         * by __block_write_begin() isn't a real problem here as we clear
         * the bit before releasing a page lock and thus writeback cannot
         * ever write the buffer.
         */
        if (dirty)
                clear_buffer_dirty(bh);
        BUFFER_TRACE(bh, "get write access");
        ret = ext4_journal_get_write_access(handle, bh);
        if (!ret && dirty)
                ret = ext4_handle_dirty_metadata(handle, NULL, bh);
        return ret;
}

static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create);
static int ext4_write_begin(struct file *file, struct address_space *mapping,
                            loff_t pos, unsigned len, unsigned flags,
                            struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        int ret, needed_blocks;
        handle_t *handle;
        int retries = 0;
        struct page *page;
        pgoff_t index;
        unsigned from, to;

        trace_ext4_write_begin(inode, pos, len, flags);
        /*
         * Reserve one block more for addition to orphan list in case
         * we allocate blocks but write fails for some reason
         */
        needed_blocks = ext4_writepage_trans_blocks(inode) + 1;
        index = pos >> PAGE_CACHE_SHIFT;
        from = pos & (PAGE_CACHE_SIZE - 1);
        to = from + len;

        if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) {
                ret = ext4_try_to_write_inline_data(mapping, inode, pos, len,
                                                    flags, pagep);
                if (ret < 0)
                        return ret;
                if (ret == 1)
                        return 0;
        }

        /*
         * grab_cache_page_write_begin() can take a long time if the
         * system is thrashing due to memory pressure, or if the page
         * is being written back.  So grab it first before we start
         * the transaction handle.  This also allows us to allocate
         * the page (if needed) without using GFP_NOFS.
         */
retry_grab:
        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page)
                return -ENOMEM;
        unlock_page(page);

retry_journal:
        handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
        if (IS_ERR(handle)) {
                page_cache_release(page);
                return PTR_ERR(handle);
        }

        lock_page(page);
        if (page->mapping != mapping) {
                /* The page got truncated from under us */
                unlock_page(page);
                page_cache_release(page);
                ext4_journal_stop(handle);
                goto retry_grab;
        }
        /* In case writeback began while the page was unlocked */
        wait_for_stable_page(page);

        if (ext4_should_dioread_nolock(inode))
                ret = __block_write_begin(page, pos, len, ext4_get_block_write);
        else
                ret = __block_write_begin(page, pos, len, ext4_get_block);

        if (!ret && ext4_should_journal_data(inode)) {
                ret = ext4_walk_page_buffers(handle, page_buffers(page),
                                             from, to, NULL,
                                             do_journal_get_write_access);
        }

        if (ret) {
                unlock_page(page);
                /*
                 * __block_write_begin may have instantiated a few blocks
                 * outside i_size.  Trim these off again. Don't need
                 * i_size_read because we hold i_mutex.
                 *
                 * Add inode to orphan list in case we crash before
                 * truncate finishes
                 */
                if (pos + len > inode->i_size && ext4_can_truncate(inode))
                        ext4_orphan_add(handle, inode);

                ext4_journal_stop(handle);
                if (pos + len > inode->i_size) {
                        ext4_truncate_failed_write(inode);
                        /*
                         * If truncate failed early the inode might
                         * still be on the orphan list; we need to
                         * make sure the inode is removed from the
                         * orphan list in that case.
                         */
                        if (inode->i_nlink)
                                ext4_orphan_del(NULL, inode);
                }

                if (ret == -ENOSPC &&
                    ext4_should_retry_alloc(inode->i_sb, &retries))
                        goto retry_journal;
                page_cache_release(page);
                return ret;
        }
        *pagep = page;
        return ret;
}

/* For write_end() in data=journal mode */
static int write_end_fn(handle_t *handle, struct buffer_head *bh)
{
        int ret;
        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        set_buffer_uptodate(bh);
        ret = ext4_handle_dirty_metadata(handle, NULL, bh);
        clear_buffer_meta(bh);
        clear_buffer_prio(bh);
        return ret;
}

/*
 * We need to pick up the new inode size which generic_commit_write gave us
 * `file' can be NULL - eg, when called from page_symlink().
 *
 * ext4 never places buffers on inode->i_mapping->private_list.  metadata
 * buffers are managed internally.
 */
static int ext4_write_end(struct file *file,
                          struct address_space *mapping,
                          loff_t pos, unsigned len, unsigned copied,
                          struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        int i_size_changed = 0;

        trace_ext4_write_end(inode, pos, len, copied);
        if (ext4_test_inode_state(inode, EXT4_STATE_ORDERED_MODE)) {
                ret = ext4_jbd2_file_inode(handle, inode);
                if (ret) {
                        unlock_page(page);
                        page_cache_release(page);
                        goto errout;
                }
        }

        if (ext4_has_inline_data(inode)) {
                ret = ext4_write_inline_data_end(inode, pos, len,
                                                 copied, page);
                if (ret < 0)
                        goto errout;
                copied = ret;
        } else
                copied = block_write_end(file, mapping, pos,
                                         len, copied, page, fsdata);
        /*
         * it's important to update i_size while still holding page lock:
         * page writeout could otherwise come in and zero beyond i_size.
         */
        i_size_changed = ext4_update_inode_size(inode, pos + copied);
        unlock_page(page);
        page_cache_release(page);

        /*
         * Don't mark the inode dirty under page lock. First, it unnecessarily
         * makes the holding time of page lock longer. Second, it forces lock
         * ordering of page lock and transaction start for journaling
         * filesystems.
         */
        if (i_size_changed)
                ext4_mark_inode_dirty(handle, inode);

        if (pos + len > inode->i_size && ext4_can_truncate(inode))
                /* if we have allocated more blocks and copied
                 * less. We will have blocks allocated outside
                 * inode->i_size. So truncate them
                 */
                ext4_orphan_add(handle, inode);
errout:
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        if (pos + len > inode->i_size) {
                ext4_truncate_failed_write(inode);
                /*
                 * If truncate failed early the inode might still be
                 * on the orphan list; we need to make sure the inode
                 * is removed from the orphan list in that case.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }

        return ret ? ret : copied;
}

static int ext4_journalled_write_end(struct file *file,
                                     struct address_space *mapping,
                                     loff_t pos, unsigned len, unsigned copied,
                                     struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        int partial = 0;
        unsigned from, to;
        int size_changed = 0;

        trace_ext4_journalled_write_end(inode, pos, len, copied);
        from = pos & (PAGE_CACHE_SIZE - 1);
        to = from + len;

        BUG_ON(!ext4_handle_valid(handle));

        if (ext4_has_inline_data(inode))
                copied = ext4_write_inline_data_end(inode, pos, len,
                                                    copied, page);
        else {
                if (copied < len) {
                        if (!PageUptodate(page))
                                copied = 0;
                        page_zero_new_buffers(page, from+copied, to);
                }

                ret = ext4_walk_page_buffers(handle, page_buffers(page), from,
                                             to, &partial, write_end_fn);
                if (!partial)
                        SetPageUptodate(page);
        }
        size_changed = ext4_update_inode_size(inode, pos + copied);
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
        EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
        unlock_page(page);
        page_cache_release(page);

        if (size_changed) {
                ret2 = ext4_mark_inode_dirty(handle, inode);
                if (!ret)
                        ret = ret2;
        }

        if (pos + len > inode->i_size && ext4_can_truncate(inode))
                /* if we have allocated more blocks and copied
                 * less. We will have blocks allocated outside
                 * inode->i_size. So truncate them
                 */
                ext4_orphan_add(handle, inode);

        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;
        if (pos + len > inode->i_size) {
                ext4_truncate_failed_write(inode);
                /*
                 * If truncate failed early the inode might still be
                 * on the orphan list; we need to make sure the inode
                 * is removed from the orphan list in that case.
                 */
                if (inode->i_nlink)
                        ext4_orphan_del(NULL, inode);
        }

        return ret ? ret : copied;
}

/*
 * Reserve a metadata for a single block located at lblock
 */
static int ext4_da_reserve_metadata(struct inode *inode, ext4_lblk_t lblock)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);
        unsigned int md_needed;
        ext4_lblk_t save_last_lblock;
        int save_len;

        /*
         * recalculate the amount of metadata blocks to reserve
         * in order to allocate nrblocks
         * worse case is one extent per block
         */
        spin_lock(&ei->i_block_reservation_lock);
        /*
         * ext4_calc_metadata_amount() has side effects, which we have
         * to be prepared undo if we fail to claim space.
         */
        save_len = ei->i_da_metadata_calc_len;
        save_last_lblock = ei->i_da_metadata_calc_last_lblock;
        md_needed = EXT4_NUM_B2C(sbi,
                                 ext4_calc_metadata_amount(inode, lblock));
        trace_ext4_da_reserve_space(inode, md_needed);

        /*
         * We do still charge estimated metadata to the sb though;
         * we cannot afford to run out of free blocks.
         */
        if (ext4_claim_free_clusters(sbi, md_needed, 0)) {
                ei->i_da_metadata_calc_len = save_len;
                ei->i_da_metadata_calc_last_lblock = save_last_lblock;
                spin_unlock(&ei->i_block_reservation_lock);
                return -ENOSPC;
        }
        ei->i_reserved_meta_blocks += md_needed;
        spin_unlock(&ei->i_block_reservation_lock);

        return 0;       /* success */
}

/*
 * Reserve a single cluster located at lblock
 */
static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);
        unsigned int md_needed;
        int ret;
        ext4_lblk_t save_last_lblock;
        int save_len;

        /*
         * We will charge metadata quota at writeout time; this saves
         * us from metadata over-estimation, though we may go over by
         * a small amount in the end.  Here we just reserve for data.
         */
        ret = dquot_reserve_block(inode, EXT4_C2B(sbi, 1));
        if (ret)
                return ret;

        /*
         * recalculate the amount of metadata blocks to reserve
         * in order to allocate nrblocks
         * worse case is one extent per block
         */
        spin_lock(&ei->i_block_reservation_lock);
        /*
         * ext4_calc_metadata_amount() has side effects, which we have
         * to be prepared undo if we fail to claim space.
         */
        save_len = ei->i_da_metadata_calc_len;
        save_last_lblock = ei->i_da_metadata_calc_last_lblock;
        md_needed = EXT4_NUM_B2C(sbi,
                                 ext4_calc_metadata_amount(inode, lblock));
        trace_ext4_da_reserve_space(inode, md_needed);

        /*
         * We do still charge estimated metadata to the sb though;
         * we cannot afford to run out of free blocks.
         */
        if (ext4_claim_free_clusters(sbi, md_needed + 1, 0)) {
                ei->i_da_metadata_calc_len = save_len;
                ei->i_da_metadata_calc_last_lblock = save_last_lblock;
                spin_unlock(&ei->i_block_reservation_lock);
                dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
                return -ENOSPC;
        }
        ei->i_reserved_data_blocks++;
        ei->i_reserved_meta_blocks += md_needed;
        spin_unlock(&ei->i_block_reservation_lock);

        return 0;       /* success */
}

static void ext4_da_release_space(struct inode *inode, int to_free)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct ext4_inode_info *ei = EXT4_I(inode);

        if (!to_free)
                return;         /* Nothing to release, exit */

        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);

        trace_ext4_da_release_space(inode, to_free);
        if (unlikely(to_free > ei->i_reserved_data_blocks)) {
                /*
                 * if there aren't enough reserved blocks, then the
                 * counter is messed up somewhere.  Since this
                 * function is called from invalidate page, it's
                 * harmless to return without any action.
                 */
                ext4_warning(inode->i_sb, "ext4_da_release_space: "
                         "ino %lu, to_free %d with only %d reserved "
                         "data blocks", inode->i_ino, to_free,
                         ei->i_reserved_data_blocks);
                WARN_ON(1);
                to_free = ei->i_reserved_data_blocks;
        }
        ei->i_reserved_data_blocks -= to_free;

        if (ei->i_reserved_data_blocks == 0) {
                /*
                 * We can release all of the reserved metadata blocks
                 * only when we have written all of the delayed
                 * allocation blocks.
                 * Note that in case of bigalloc, i_reserved_meta_blocks,
                 * i_reserved_data_blocks, etc. refer to number of clusters.
                 */
                percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                                   ei->i_reserved_meta_blocks);
                ei->i_reserved_meta_blocks = 0;
                ei->i_da_metadata_calc_len = 0;
        }

        /* update fs dirty data blocks counter */
        percpu_counter_sub(&sbi->s_dirtyclusters_counter, to_free);

        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

        dquot_release_reservation_block(inode, EXT4_C2B(sbi, to_free));
}

static void ext4_da_page_release_reservation(struct page *page,
                                             unsigned int offset,
                                             unsigned int length)
{
        int to_release = 0, contiguous_blks = 0;
        struct buffer_head *head, *bh;
        unsigned int curr_off = 0;
        struct inode *inode = page->mapping->host;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        unsigned int stop = offset + length;
        int num_clusters;
        ext4_fsblk_t lblk;

        BUG_ON(stop > PAGE_CACHE_SIZE || stop < length);

        head = page_buffers(page);
        bh = head;
        do {
                unsigned int next_off = curr_off + bh->b_size;

                if (next_off > stop)
                        break;

                if ((offset <= curr_off) && (buffer_delay(bh))) {
                        to_release++;
                        contiguous_blks++;
                        clear_buffer_delay(bh);
                } else if (contiguous_blks) {
                        lblk = page->index <<
                               (PAGE_CACHE_SHIFT - inode->i_blkbits);
                        lblk += (curr_off >> inode->i_blkbits) -
                                contiguous_blks;
                        ext4_es_remove_extent(inode, lblk, contiguous_blks);
                        contiguous_blks = 0;
                }
                curr_off = next_off;
        } while ((bh = bh->b_this_page) != head);

        if (contiguous_blks) {
                lblk = page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
                lblk += (curr_off >> inode->i_blkbits) - contiguous_blks;
                ext4_es_remove_extent(inode, lblk, contiguous_blks);
        }

        /* If we have released all the blocks belonging to a cluster, then we
         * need to release the reserved space for that cluster. */
        num_clusters = EXT4_NUM_B2C(sbi, to_release);
        while (num_clusters > 0) {
                lblk = (page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits)) +
                        ((num_clusters - 1) << sbi->s_cluster_bits);
                if (sbi->s_cluster_ratio == 1 ||
                    !ext4_find_delalloc_cluster(inode, lblk))
                        ext4_da_release_space(inode, 1);

                num_clusters--;
        }
}

/*
 * Delayed allocation stuff
 */

struct mpage_da_data {
        struct inode *inode;
        struct writeback_control *wbc;

        pgoff_t first_page;     /* The first page to write */
        pgoff_t next_page;      /* Current page to examine */
        pgoff_t last_page;      /* Last page to examine */
        /*
         * Extent to map - this can be after first_page because that can be
         * fully mapped. We somewhat abuse m_flags to store whether the extent
         * is delalloc or unwritten.
         */
        struct ext4_map_blocks map;
        struct ext4_io_submit io_submit;        /* IO submission data */
};

static void mpage_release_unused_pages(struct mpage_da_data *mpd,
                                       bool invalidate)
{
        int nr_pages, i;
        pgoff_t index, end;
        struct pagevec pvec;
        struct inode *inode = mpd->inode;
        struct address_space *mapping = inode->i_mapping;

        /* This is necessary when next_page == 0. */
        if (mpd->first_page >= mpd->next_page)
                return;

        index = mpd->first_page;
        end   = mpd->next_page - 1;
        if (invalidate) {
                ext4_lblk_t start, last;
                start = index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
                last = end << (PAGE_CACHE_SHIFT - inode->i_blkbits);
                ext4_es_remove_extent(inode, start, last - start + 1);
        }

        pagevec_init(&pvec, 0);
        while (index <= end) {
                nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];
                        if (page->index > end)
                                break;
                        BUG_ON(!PageLocked(page));
                        BUG_ON(PageWriteback(page));
                        if (invalidate) {
                                block_invalidatepage(page, 0, PAGE_CACHE_SIZE);
                                ClearPageUptodate(page);
                        }
                        unlock_page(page);
                }
                index = pvec.pages[nr_pages - 1]->index + 1;
                pagevec_release(&pvec);
        }
}

static void ext4_print_free_blocks(struct inode *inode)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        struct super_block *sb = inode->i_sb;
        struct ext4_inode_info *ei = EXT4_I(inode);

        ext4_msg(sb, KERN_CRIT, "Total free blocks count %lld",
               EXT4_C2B(EXT4_SB(inode->i_sb),
                        ext4_count_free_clusters(sb)));
        ext4_msg(sb, KERN_CRIT, "Free/Dirty block details");
        ext4_msg(sb, KERN_CRIT, "free_blocks=%lld",
               (long long) EXT4_C2B(EXT4_SB(sb),
                percpu_counter_sum(&sbi->s_freeclusters_counter)));
        ext4_msg(sb, KERN_CRIT, "dirty_blocks=%lld",
               (long long) EXT4_C2B(EXT4_SB(sb),
                percpu_counter_sum(&sbi->s_dirtyclusters_counter)));
        ext4_msg(sb, KERN_CRIT, "Block reservation details");
        ext4_msg(sb, KERN_CRIT, "i_reserved_data_blocks=%u",
                 ei->i_reserved_data_blocks);
        ext4_msg(sb, KERN_CRIT, "i_reserved_meta_blocks=%u",
               ei->i_reserved_meta_blocks);
        ext4_msg(sb, KERN_CRIT, "i_allocated_meta_blocks=%u",
               ei->i_allocated_meta_blocks);
        return;
}

static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
{
        return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
}

/*
 * This function is grabs code from the very beginning of
 * ext4_map_blocks, but assumes that the caller is from delayed write
 * time. This function looks up the requested blocks and sets the
 * buffer delay bit under the protection of i_data_sem.
 */
static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
                              struct ext4_map_blocks *map,
                              struct buffer_head *bh)
{
        struct extent_status es;
        int retval;
        sector_t invalid_block = ~((sector_t) 0xffff);
#ifdef ES_AGGRESSIVE_TEST
        struct ext4_map_blocks orig_map;

        memcpy(&orig_map, map, sizeof(*map));
#endif

        if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
                invalid_block = ~0;

        map->m_flags = 0;
        ext_debug("ext4_da_map_blocks(): inode %lu, max_blocks %u,"
                  "logical block %lu\n", inode->i_ino, map->m_len,
                  (unsigned long) map->m_lblk);

        /* Lookup extent status tree firstly */
        if (ext4_es_lookup_extent(inode, iblock, &es)) {
                ext4_es_lru_add(inode);
                if (ext4_es_is_hole(&es)) {
                        retval = 0;
                        down_read(&EXT4_I(inode)->i_data_sem);
                        goto add_delayed;
                }

                /*
                 * Delayed extent could be allocated by fallocate.
                 * So we need to check it.
                 */
                if (ext4_es_is_delayed(&es) && !ext4_es_is_unwritten(&es)) {
                        map_bh(bh, inode->i_sb, invalid_block);
                        set_buffer_new(bh);
                        set_buffer_delay(bh);
                        return 0;
                }

                map->m_pblk = ext4_es_pblock(&es) + iblock - es.es_lblk;
                retval = es.es_len - (iblock - es.es_lblk);
                if (retval > map->m_len)
                        retval = map->m_len;
                map->m_len = retval;
                if (ext4_es_is_written(&es))
                        map->m_flags |= EXT4_MAP_MAPPED;
                else if (ext4_es_is_unwritten(&es))
                        map->m_flags |= EXT4_MAP_UNWRITTEN;
                else
                        BUG_ON(1);

#ifdef ES_AGGRESSIVE_TEST
                ext4_map_blocks_es_recheck(NULL, inode, map, &orig_map, 0);
#endif
                return retval;
        }

        /*
         * Try to see if we can get the block without requesting a new
         * file system block.
         */
        down_read(&EXT4_I(inode)->i_data_sem);
        if (ext4_has_inline_data(inode)) {
                /*
                 * We will soon create blocks for this page, and let
                 * us pretend as if the blocks aren't allocated yet.
                 * In case of clusters, we have to handle the work
                 * of mapping from cluster so that the reserved space
                 * is calculated properly.
                 */
                if ((EXT4_SB(inode->i_sb)->s_cluster_ratio > 1) &&
                    ext4_find_delalloc_cluster(inode, map->m_lblk))
                        map->m_flags |= EXT4_MAP_FROM_CLUSTER;
                retval = 0;
        } else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                retval = ext4_ext_map_blocks(NULL, inode, map,
                                             EXT4_GET_BLOCKS_NO_PUT_HOLE);
        else
                retval = ext4_ind_map_blocks(NULL, inode, map,
                                             EXT4_GET_BLOCKS_NO_PUT_HOLE);

add_delayed:
        if (retval == 0) {
                int ret;
                /*
                 * XXX: __block_prepare_write() unmaps passed block,
                 * is it OK?
                 */
                /*
                 * If the block was allocated from previously allocated cluster,
                 * then we don't need to reserve it again. However we still need
                 * to reserve metadata for every block we're going to write.
                 */
                if (!(map->m_flags & EXT4_MAP_FROM_CLUSTER)) {
                        ret = ext4_da_reserve_space(inode, iblock);
                        if (ret) {
                                /* not enough space to reserve */
                                retval = ret;
                                goto out_unlock;
                        }
                } else {
                        ret = ext4_da_reserve_metadata(inode, iblock);
                        if (ret) {
                                /* not enough space to reserve */
                                retval = ret;
                                goto out_unlock;
                        }
                }

                ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
                                            ~0, EXTENT_STATUS_DELAYED);
                if (ret) {
                        retval = ret;
                        goto out_unlock;
                }

                /* Clear EXT4_MAP_FROM_CLUSTER flag since its purpose is served
                 * and it should not appear on the bh->b_state.
                 */
                map->m_flags &= ~EXT4_MAP_FROM_CLUSTER;

                map_bh(bh, inode->i_sb, invalid_block);
                set_buffer_new(bh);
                set_buffer_delay(bh);
        } else if (retval > 0) {
                int ret;
                unsigned int status;

                if (unlikely(retval != map->m_len)) {
                        ext4_warning(inode->i_sb,
                                     "ES len assertion failed for inode "
                                     "%lu: retval %d != map->m_len %d",
                                     inode->i_ino, retval, map->m_len);
                        WARN_ON(1);
                }

                status = map->m_flags & EXT4_MAP_UNWRITTEN ?
                                EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
                ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
                                            map->m_pblk, status);
                if (ret != 0)
                        retval = ret;
        }

out_unlock:
        up_read((&EXT4_I(inode)->i_data_sem));

        return retval;
}

/*
 * This is a special get_blocks_t callback which is used by
 * ext4_da_write_begin().  It will either return mapped block or
 * reserve space for a single block.
 *
 * For delayed buffer_head we have BH_Mapped, BH_New, BH_Delay set.
 * We also have b_blocknr = -1 and b_bdev initialized properly
 *
 * For unwritten buffer_head we have BH_Mapped, BH_New, BH_Unwritten set.
 * We also have b_blocknr = physicalblock mapping unwritten extent and b_bdev
 * initialized properly.
 */
int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                           struct buffer_head *bh, int create)
{
        struct ext4_map_blocks map;
        int ret = 0;

        BUG_ON(create == 0);
        BUG_ON(bh->b_size != inode->i_sb->s_blocksize);

        map.m_lblk = iblock;
        map.m_len = 1;

        /*
         * first, we need to know whether the block is allocated already
         * preallocated blocks are unmapped but should treated
         * the same as allocated blocks.
         */
        ret = ext4_da_map_blocks(inode, iblock, &map, bh);
        if (ret <= 0)
                return ret;

        map_bh(bh, inode->i_sb, map.m_pblk);
        ext4_update_bh_state(bh, map.m_flags);

        if (buffer_unwritten(bh)) {
                /* A delayed write to unwritten bh should be marked
                 * new and mapped.  Mapped ensures that we don't do
                 * get_block multiple times when we write to the same
                 * offset and new ensures that we do proper zero out
                 * for partial write.
                 */
                set_buffer_new(bh);
                set_buffer_mapped(bh);
        }
        return 0;
}

static int bget_one(handle_t *handle, struct buffer_head *bh)
{
        get_bh(bh);
        return 0;
}

static int bput_one(handle_t *handle, struct buffer_head *bh)
{
        put_bh(bh);
        return 0;
}

static int __ext4_journalled_writepage(struct page *page,
                                       unsigned int len)
{
        struct address_space *mapping = page->mapping;
        struct inode *inode = mapping->host;
        struct buffer_head *page_bufs = NULL;
        handle_t *handle = NULL;
        int ret = 0, err = 0;
        int inline_data = ext4_has_inline_data(inode);
        struct buffer_head *inode_bh = NULL;

        ClearPageChecked(page);

        if (inline_data) {
                BUG_ON(page->index != 0);
                BUG_ON(len > ext4_get_max_inline_size(inode));
                inode_bh = ext4_journalled_write_inline_data(inode, len, page);
                if (inode_bh == NULL)
                        goto out;
        } else {
                page_bufs = page_buffers(page);
                if (!page_bufs) {
                        BUG();
                        goto out;
                }
                ext4_walk_page_buffers(handle, page_bufs, 0, len,
                                       NULL, bget_one);
        }
        /*
         * We need to release the page lock before we start the
         * journal, so grab a reference so the page won't disappear
         * out from under us.
         */
        get_page(page);
        unlock_page(page);

        handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
                                    ext4_writepage_trans_blocks(inode));
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                put_page(page);
                goto out_no_pagelock;
        }
        BUG_ON(!ext4_handle_valid(handle));

        lock_page(page);
        put_page(page);
        if (page->mapping != mapping) {
                /* The page got truncated from under us */
                ext4_journal_stop(handle);
                ret = 0;
                goto out;
        }

        if (inline_data) {
                BUFFER_TRACE(inode_bh, "get write access");
                ret = ext4_journal_get_write_access(handle, inode_bh);

                err = ext4_handle_dirty_metadata(handle, inode, inode_bh);

        } else {
                ret = ext4_walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                             do_journal_get_write_access);

                err = ext4_walk_page_buffers(handle, page_bufs, 0, len, NULL,
                                             write_end_fn);
        }
        if (ret == 0)
                ret = err;
        EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
        err = ext4_journal_stop(handle);
        if (!ret)
                ret = err;

        if (!ext4_has_inline_data(inode))
                ext4_walk_page_buffers(NULL, page_bufs, 0, len,
                                       NULL, bput_one);
        ext4_set_inode_state(inode, EXT4_STATE_JDATA);
out:
        unlock_page(page);
out_no_pagelock:
        brelse(inode_bh);
        return ret;
}

/*
 * Note that we don't need to start a transaction unless we're journaling data
 * because we should have holes filled from ext4_page_mkwrite(). We even don't
 * need to file the inode to the transaction's list in ordered mode because if
 * we are writing back data added by write(), the inode is already there and if
 * we are writing back data modified via mmap(), no one guarantees in which
 * transaction the data will hit the disk. In case we are journaling data, we
 * cannot start transaction directly because transaction start ranks above page
 * lock so we have to do some magic.
 *
 * This function can get called via...
 *   - ext4_writepages after taking page lock (have journal handle)
 *   - journal_submit_inode_data_buffers (no journal handle)
 *   - shrink_page_list via the kswapd/direct reclaim (no journal handle)
 *   - grab_page_cache when doing write_begin (have journal handle)
 *
 * We don't do any block allocation in this function. If we have page with
 * multiple blocks we need to write those buffer_heads that are mapped. This
 * is important for mmaped based write. So if we do with blocksize 1K
 * truncate(f, 1024);
 * a = mmap(f, 0, 4096);
 * a[0] = 'a';
 * truncate(f, 4096);
 * we have in the page first buffer_head mapped via page_mkwrite call back
 * but other buffer_heads would be unmapped but dirty (dirty done via the
 * do_wp_page). So writepage should write the first block. If we modify
 * the mmap area beyond 1024 we will again get a page_fault and the
 * page_mkwrite callback will do the block allocation and mark the
 * buffer_heads mapped.
 *
 * We redirty the page if we have any buffer_heads that is either delay or
 * unwritten in the page.
 *
 * We can get recursively called as show below.
 *
 *      ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
 *              ext4_writepage()
 *
 * But since we don't do any block allocation we should not deadlock.
 * Page also have the dirty flag cleared so we don't get recurive page_lock.
 */
static int ext4_writepage(struct page *page,
                          struct writeback_control *wbc)
{
        int ret = 0;
        loff_t size;
        unsigned int len;
        struct buffer_head *page_bufs = NULL;
        struct inode *inode = page->mapping->host;
        struct ext4_io_submit io_submit;
        bool keep_towrite = false;

        trace_ext4_writepage(page);
        size = i_size_read(inode);
        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;

        page_bufs = page_buffers(page);
        /*
         * We cannot do block allocation or other extent handling in this
         * function. If there are buffers needing that, we have to redirty
         * the page. But we may reach here when we do a journal commit via
         * journal_submit_inode_data_buffers() and in that case we must write
         * allocated buffers to achieve data=ordered mode guarantees.
         */
        if (ext4_walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                                   ext4_bh_delay_or_unwritten)) {
                redirty_page_for_writepage(wbc, page);
                if (current->flags & PF_MEMALLOC) {
                        /*
                         * For memory cleaning there's no point in writing only
                         * some buffers. So just bail out. Warn if we came here
                         * from direct reclaim.
                         */
                        WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD))
                                                        == PF_MEMALLOC);
                        unlock_page(page);
                        return 0;
                }
                keep_towrite = true;
        }

        if (PageChecked(page) && ext4_should_journal_data(inode))
                /*
                 * It's mmapped pagecache.  Add buffers and journal it.  There
                 * doesn't seem much point in redirtying the page here.
                 */
                return __ext4_journalled_writepage(page, len);

        ext4_io_submit_init(&io_submit, wbc);
        io_submit.io_end = ext4_init_io_end(inode, GFP_NOFS);
        if (!io_submit.io_end) {
                redirty_page_for_writepage(wbc, page);
                unlock_page(page);
                return -ENOMEM;
        }
        ret = ext4_bio_write_page(&io_submit, page, len, wbc, keep_towrite);
        ext4_io_submit(&io_submit);
        /* Drop io_end reference we got from init */
        ext4_put_io_end_defer(io_submit.io_end);
        return ret;
}

static int mpage_submit_page(struct mpage_da_data *mpd, struct page *page)
{
        int len;
        loff_t size = i_size_read(mpd->inode);
        int err;

        BUG_ON(page->index != mpd->first_page);
        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;
        clear_page_dirty_for_io(page);
        err = ext4_bio_write_page(&mpd->io_submit, page, len, mpd->wbc, false);
        if (!err)
                mpd->wbc->nr_to_write--;
        mpd->first_page++;

        return err;
}

#define BH_FLAGS ((1 << BH_Unwritten) | (1 << BH_Delay))

/*
 * mballoc gives us at most this number of blocks...
 * XXX: That seems to be only a limitation of ext4_mb_normalize_request().
 * The rest of mballoc seems to handle chunks up to full group size.
 */
#define MAX_WRITEPAGES_EXTENT_LEN 2048

/*
 * mpage_add_bh_to_extent - try to add bh to extent of blocks to map
 *
 * @mpd - extent of blocks
 * @lblk - logical number of the block in the file
 * @bh - buffer head we want to add to the extent
 *
 * The function is used to collect contig. blocks in the same state. If the
 * buffer doesn't require mapping for writeback and we haven't started the
 * extent of buffers to map yet, the function returns 'true' immediately - the
 * caller can write the buffer right away. Otherwise the function returns true
 * if the block has been added to the extent, false if the block couldn't be
 * added.
 */
static bool mpage_add_bh_to_extent(struct mpage_da_data *mpd, ext4_lblk_t lblk,
                                   struct buffer_head *bh)
{
        struct ext4_map_blocks *map = &mpd->map;

        /* Buffer that doesn't need mapping for writeback? */
        if (!buffer_dirty(bh) || !buffer_mapped(bh) ||
            (!buffer_delay(bh) && !buffer_unwritten(bh))) {
                /* So far no extent to map => we write the buffer right away */
                if (map->m_len == 0)
                        return true;
                return false;
        }

        /* First block in the extent? */
        if (map->m_len == 0) {
                map->m_lblk = lblk;
                map->m_len = 1;
                map->m_flags = bh->b_state & BH_FLAGS;
                return true;
        }

        /* Don't go larger than mballoc is willing to allocate */
        if (map->m_len >= MAX_WRITEPAGES_EXTENT_LEN)
                return false;

        /* Can we merge the block to our big extent? */
        if (lblk == map->m_lblk + map->m_len &&
            (bh->b_state & BH_FLAGS) == map->m_flags) {
                map->m_len++;
                return true;
        }
        return false;
}

/*
 * mpage_process_page_bufs - submit page buffers for IO or add them to extent
 *
 * @mpd - extent of blocks for mapping
 * @head - the first buffer in the page
 * @bh - buffer we should start processing from
 * @lblk - logical number of the block in the file corresponding to @bh
 *
 * Walk through page buffers from @bh upto @head (exclusive) and either submit
 * the page for IO if all buffers in this page were mapped and there's no
 * accumulated extent of buffers to map or add buffers in the page to the
 * extent of buffers to map. The function returns 1 if the caller can continue
 * by processing the next page, 0 if it should stop adding buffers to the
 * extent to map because we cannot extend it anymore. It can also return value
 * < 0 in case of error during IO submission.
 */
static int mpage_process_page_bufs(struct mpage_da_data *mpd,
                                   struct buffer_head *head,
                                   struct buffer_head *bh,
                                   ext4_lblk_t lblk)
{
        struct inode *inode = mpd->inode;
        int err;
        ext4_lblk_t blocks = (i_size_read(inode) + (1 << inode->i_blkbits) - 1)
                                                        >> inode->i_blkbits;

        do {
                BUG_ON(buffer_locked(bh));

                if (lblk >= blocks || !mpage_add_bh_to_extent(mpd, lblk, bh)) {
                        /* Found extent to map? */
                        if (mpd->map.m_len)
                                return 0;
                        /* Everything mapped so far and we hit EOF */
                        break;
                }
        } while (lblk++, (bh = bh->b_this_page) != head);
        /* So far everything mapped? Submit the page for IO. */
        if (mpd->map.m_len == 0) {
                err = mpage_submit_page(mpd, head->b_page);
                if (err < 0)
                        return err;
        }
        return lblk < blocks;
}

/*
 * mpage_map_buffers - update buffers corresponding to changed extent and
 *                     submit fully mapped pages for IO
 *
 * @mpd - description of extent to map, on return next extent to map
 *
 * Scan buffers corresponding to changed extent (we expect corresponding pages
 * to be already locked) and update buffer state according to new extent state.
 * We map delalloc buffers to their physical location, clear unwritten bits,
 * and mark buffers as uninit when we perform writes to unwritten extents
 * and do extent conversion after IO is finished. If the last page is not fully
 * mapped, we update @map to the next extent in the last page that needs
 * mapping. Otherwise we submit the page for IO.
 */
static int mpage_map_and_submit_buffers(struct mpage_da_data *mpd)
{
        struct pagevec pvec;
        int nr_pages, i;
        struct inode *inode = mpd->inode;
        struct buffer_head *head, *bh;
        int bpp_bits = PAGE_CACHE_SHIFT - inode->i_blkbits;
        pgoff_t start, end;
        ext4_lblk_t lblk;
        sector_t pblock;
        int err;

        start = mpd->map.m_lblk >> bpp_bits;
        end = (mpd->map.m_lblk + mpd->map.m_len - 1) >> bpp_bits;
        lblk = start << bpp_bits;
        pblock = mpd->map.m_pblk;

        pagevec_init(&pvec, 0);
        while (start <= end) {
                nr_pages = pagevec_lookup(&pvec, inode->i_mapping, start,
                                          PAGEVEC_SIZE);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        if (page->index > end)
                                break;
                        /* Up to 'end' pages must be contiguous */
                        BUG_ON(page->index != start);
                        bh = head = page_buffers(page);
                        do {
                                if (lblk < mpd->map.m_lblk)
                                        continue;
                                if (lblk >= mpd->map.m_lblk + mpd->map.m_len) {
                                        /*
                                         * Buffer after end of mapped extent.
                                         * Find next buffer in the page to map.
                                         */
                                        mpd->map.m_len = 0;
                                        mpd->map.m_flags = 0;
                                        /*
                                         * FIXME: If dioread_nolock supports
                                         * blocksize < pagesize, we need to make
                                         * sure we add size mapped so far to
                                         * io_end->size as the following call
                                         * can submit the page for IO.
                                         */
                                        err = mpage_process_page_bufs(mpd, head,
                                                                      bh, lblk);
                                        pagevec_release(&pvec);
                                        if (err > 0)
                                                err = 0;
                                        return err;
                                }
                                if (buffer_delay(bh)) {
                                        clear_buffer_delay(bh);
                                        bh->b_blocknr = pblock++;
                                }
                                clear_buffer_unwritten(bh);
                        } while (lblk++, (bh = bh->b_this_page) != head);

                        /*
                         * FIXME: This is going to break if dioread_nolock
                         * supports blocksize < pagesize as we will try to
                         * convert potentially unmapped parts of inode.
                         */
                        mpd->io_submit.io_end->size += PAGE_CACHE_SIZE;
                        /* Page fully mapped - let IO run! */
                        err = mpage_submit_page(mpd, page);
                        if (err < 0) {
                                pagevec_release(&pvec);
                                return err;
                        }
                        start++;
                }
                pagevec_release(&pvec);
        }
        /* Extent fully mapped and matches with page boundary. We are done. */
        mpd->map.m_len = 0;
        mpd->map.m_flags = 0;
        return 0;
}

static int mpage_map_one_extent(handle_t *handle, struct mpage_da_data *mpd)
{
        struct inode *inode = mpd->inode;
        struct ext4_map_blocks *map = &mpd->map;
        int get_blocks_flags;
        int err, dioread_nolock;

        trace_ext4_da_write_pages_extent(inode, map);
        /*
         * Call ext4_map_blocks() to allocate any delayed allocation blocks, or
         * to convert an unwritten extent to be initialized (in the case
         * where we have written into one or more preallocated blocks).  It is
         * possible that we're going to need more metadata blocks than
         * previously reserved. However we must not fail because we're in
         * writeback and there is nothing we can do about it so it might result
         * in data loss.  So use reserved blocks to allocate metadata if
         * possible.
         *
         * We pass in the magic EXT4_GET_BLOCKS_DELALLOC_RESERVE if the blocks
         * in question are delalloc blocks.  This affects functions in many
         * different parts of the allocation call path.  This flag exists
         * primarily because we don't want to change *many* call functions, so
         * ext4_map_blocks() will set the EXT4_STATE_DELALLOC_RESERVED flag
         * once the inode's allocation semaphore is taken.
         */
        get_blocks_flags = EXT4_GET_BLOCKS_CREATE |
                           EXT4_GET_BLOCKS_METADATA_NOFAIL;
        dioread_nolock = ext4_should_dioread_nolock(inode);
        if (dioread_nolock)
                get_blocks_flags |= EXT4_GET_BLOCKS_IO_CREATE_EXT;
        if (map->m_flags & (1 << BH_Delay))
                get_blocks_flags |= EXT4_GET_BLOCKS_DELALLOC_RESERVE;

        err = ext4_map_blocks(handle, inode, map, get_blocks_flags);
        if (err < 0)
                return err;
        if (dioread_nolock && (map->m_flags & EXT4_MAP_UNWRITTEN)) {
                if (!mpd->io_submit.io_end->handle &&
                    ext4_handle_valid(handle)) {
                        mpd->io_submit.io_end->handle = handle->h_rsv_handle;
                        handle->h_rsv_handle = NULL;
                }
                ext4_set_io_unwritten_flag(inode, mpd->io_submit.io_end);
        }

        BUG_ON(map->m_len == 0);
        if (map->m_flags & EXT4_MAP_NEW) {
                struct block_device *bdev = inode->i_sb->s_bdev;
                int i;

                for (i = 0; i < map->m_len; i++)
                        unmap_underlying_metadata(bdev, map->m_pblk + i);
        }
        return 0;
}

/*
 * mpage_map_and_submit_extent - map extent starting at mpd->lblk of length
 *                               mpd->len and submit pages underlying it for IO
 *
 * @handle - handle for journal operations
 * @mpd - extent to map
 * @give_up_on_write - we set this to true iff there is a fatal error and there
 *                     is no hope of writing the data. The caller should discard
 *                     dirty pages to avoid infinite loops.
 *
 * The function maps extent starting at mpd->lblk of length mpd->len. If it is
 * delayed, blocks are allocated, if it is unwritten, we may need to convert
 * them to initialized or split the described range from larger unwritten
 * extent. Note that we need not map all the described range since allocation
 * can return less blocks or the range is covered by more unwritten extents. We
 * cannot map more because we are limited by reserved transaction credits. On
 * the other hand we always make sure that the last touched page is fully
 * mapped so that it can be written out (and thus forward progress is
 * guaranteed). After mapping we submit all mapped pages for IO.
 */
static int mpage_map_and_submit_extent(handle_t *handle,
                                       struct mpage_da_data *mpd,
                                       bool *give_up_on_write)
{
        struct inode *inode = mpd->inode;
        struct ext4_map_blocks *map = &mpd->map;
        int err;
        loff_t disksize;
        int progress = 0;

        mpd->io_submit.io_end->offset =
                                ((loff_t)map->m_lblk) << inode->i_blkbits;
        do {
                err = mpage_map_one_extent(handle, mpd);
                if (err < 0) {
                        struct super_block *sb = inode->i_sb;

                        if (EXT4_SB(sb)->s_mount_flags & EXT4_MF_FS_ABORTED)
                                goto invalidate_dirty_pages;
                        /*
                         * Let the uper layers retry transient errors.
                         * In the case of ENOSPC, if ext4_count_free_blocks()
                         * is non-zero, a commit should free up blocks.
                         */
                        if ((err == -ENOMEM) ||
                            (err == -ENOSPC && ext4_count_free_clusters(sb))) {
                                if (progress)
                                        goto update_disksize;
                                return err;
                        }
                        ext4_msg(sb, KERN_CRIT,
                                 "Delayed block allocation failed for "
                                 "inode %lu at logical offset %llu with"
                                 " max blocks %u with error %d",
                                 inode->i_ino,
                                 (unsigned long long)map->m_lblk,
                                 (unsigned)map->m_len, -err);
                        ext4_msg(sb, KERN_CRIT,
                                 "This should not happen!! Data will "
                                 "be lost\n");
                        if (err == -ENOSPC)
                                ext4_print_free_blocks(inode);
                invalidate_dirty_pages:
                        *give_up_on_write = true;
                        return err;
                }
                progress = 1;
                /*
                 * Update buffer state, submit mapped pages, and get us new
                 * extent to map
                 */
                err = mpage_map_and_submit_buffers(mpd);
                if (err < 0)
                        goto update_disksize;
        } while (map->m_len);

update_disksize:
        /*
         * Update on-disk size after IO is submitted.  Races with
         * truncate are avoided by checking i_size under i_data_sem.
         */
        disksize = ((loff_t)mpd->first_page) << PAGE_CACHE_SHIFT;
        if (disksize > EXT4_I(inode)->i_disksize) {
                int err2;
                loff_t i_size;

                down_write(&EXT4_I(inode)->i_data_sem);
                i_size = i_size_read(inode);
                if (disksize > i_size)
                        disksize = i_size;
                if (disksize > EXT4_I(inode)->i_disksize)
                        EXT4_I(inode)->i_disksize = disksize;
                err2 = ext4_mark_inode_dirty(handle, inode);
                up_write(&EXT4_I(inode)->i_data_sem);
                if (err2)
                        ext4_error(inode->i_sb,
                                   "Failed to mark inode %lu dirty",
                                   inode->i_ino);
                if (!err)
                        err = err2;
        }
        return err;
}

/*
 * Calculate the total number of credits to reserve for one writepages
 * iteration. This is called from ext4_writepages(). We map an extent of
 * up to MAX_WRITEPAGES_EXTENT_LEN blocks and then we go on and finish mapping
 * the last partial page. So in total we can map MAX_WRITEPAGES_EXTENT_LEN +
 * bpp - 1 blocks in bpp different extents.
 */
static int ext4_da_writepages_trans_blocks(struct inode *inode)
{
        int bpp = ext4_journal_blocks_per_page(inode);

        return ext4_meta_trans_blocks(inode,
                                MAX_WRITEPAGES_EXTENT_LEN + bpp - 1, bpp);
}

/*
 * mpage_prepare_extent_to_map - find & lock contiguous range of dirty pages
 *                               and underlying extent to map
 *
 * @mpd - where to look for pages
 *
 * Walk dirty pages in the mapping. If they are fully mapped, submit them for
 * IO immediately. When we find a page which isn't mapped we start accumulating
 * extent of buffers underlying these pages that needs mapping (formed by
 * either delayed or unwritten buffers). We also lock the pages containing
 * these buffers. The extent found is returned in @mpd structure (starting at
 * mpd->lblk with length mpd->len blocks).
 *
 * Note that this function can attach bios to one io_end structure which are
 * neither logically nor physically contiguous. Although it may seem as an
 * unnecessary complication, it is actually inevitable in blocksize < pagesize
 * case as we need to track IO to all buffers underlying a page in one io_end.
 */
static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
{
        struct address_space *mapping = mpd->inode->i_mapping;
        struct pagevec pvec;
        unsigned int nr_pages;
        long left = mpd->wbc->nr_to_write;
        pgoff_t index = mpd->first_page;
        pgoff_t end = mpd->last_page;
        int tag;
        int i, err = 0;
        int blkbits = mpd->inode->i_blkbits;
        ext4_lblk_t lblk;
        struct buffer_head *head;

        if (mpd->wbc->sync_mode == WB_SYNC_ALL || mpd->wbc->tagged_writepages)
                tag = PAGECACHE_TAG_TOWRITE;
        else
                tag = PAGECACHE_TAG_DIRTY;

        pagevec_init(&pvec, 0);
        mpd->map.m_len = 0;
        mpd->next_page = index;
        while (index <= end) {
                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
                if (nr_pages == 0)
                        goto out;

                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        /*
                         * At this point, the page may be truncated or
                         * invalidated (changing page->mapping to NULL), or
                         * even swizzled back from swapper_space to tmpfs file
                         * mapping. However, page->index will not change
                         * because we have a reference on the page.
                         */
                        if (page->index > end)
                                goto out;

                        /*
                         * Accumulated enough dirty pages? This doesn't apply
                         * to WB_SYNC_ALL mode. For integrity sync we have to
                         * keep going because someone may be concurrently
                         * dirtying pages, and we might have synced a lot of
                         * newly appeared dirty pages, but have not synced all
                         * of the old dirty pages.
                         */
                        if (mpd->wbc->sync_mode == WB_SYNC_NONE && left <= 0)
                                goto out;

                        /* If we can't merge this page, we are done. */
                        if (mpd->map.m_len > 0 && mpd->next_page != page->index)
                                goto out;

                        lock_page(page);
                        /*
                         * If the page is no longer dirty, or its mapping no
                         * longer corresponds to inode we are writing (which
                         * means it has been truncated or invalidated), or the
                         * page is already under writeback and we are not doing
                         * a data integrity writeback, skip the page
                         */
                        if (!PageDirty(page) ||
                            (PageWriteback(page) &&
                             (mpd->wbc->sync_mode == WB_SYNC_NONE)) ||
                            unlikely(page->mapping != mapping)) {
                                unlock_page(page);
                                continue;
                        }

                        wait_on_page_writeback(page);
                        BUG_ON(PageWriteback(page));

                        if (mpd->map.m_len == 0)
                                mpd->first_page = page->index;
                        mpd->next_page = page->index + 1;
                        /* Add all dirty buffers to mpd */
                        lblk = ((ext4_lblk_t)page->index) <<
                                (PAGE_CACHE_SHIFT - blkbits);
                        head = page_buffers(page);
                        err = mpage_process_page_bufs(mpd, head, head, lblk);
                        if (err <= 0)
                                goto out;
                        err = 0;
                        left--;
                }
                pagevec_release(&pvec);
                cond_resched();
        }
        return 0;
out:
        pagevec_release(&pvec);
        return err;
}

static int __writepage(struct page *page, struct writeback_control *wbc,
                       void *data)
{
        struct address_space *mapping = data;
        int ret = ext4_writepage(page, wbc);
        mapping_set_error(mapping, ret);
        return ret;
}

static int ext4_writepages(struct address_space *mapping,
                           struct writeback_control *wbc)
{
        pgoff_t writeback_index = 0;
        long nr_to_write = wbc->nr_to_write;
        int range_whole = 0;
        int cycled = 1;
        handle_t *handle = NULL;
        struct mpage_da_data mpd;
        struct inode *inode = mapping->host;
        int needed_blocks, rsv_blocks = 0, ret = 0;
        struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
        bool done;
        struct blk_plug plug;
        bool give_up_on_write = false;

        trace_ext4_writepages(inode, wbc);

        /*
         * No pages to write? This is mainly a kludge to avoid starting
         * a transaction for special inodes like journal inode on last iput()
         * because that could violate lock ordering on umount
         */
        if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                goto out_writepages;

        if (ext4_should_journal_data(inode)) {
                struct blk_plug plug;

                blk_start_plug(&plug);
                ret = write_cache_pages(mapping, wbc, __writepage, mapping);
                blk_finish_plug(&plug);
                goto out_writepages;
        }

        /*
         * If the filesystem has aborted, it is read-only, so return
         * right away instead of dumping stack traces later on that
         * will obscure the real source of the problem.  We test
         * EXT4_MF_FS_ABORTED instead of sb->s_flag's MS_RDONLY because
         * the latter could be true if the filesystem is mounted
         * read-only, and in that case, ext4_writepages should
         * *never* be called, so if that ever happens, we would want
         * the stack trace.
         */
        if (unlikely(sbi->s_mount_flags & EXT4_MF_FS_ABORTED)) {
                ret = -EROFS;
                goto out_writepages;
        }

        if (ext4_should_dioread_nolock(inode)) {
                /*
                 * We may need to convert up to one extent per block in
                 * the page and we may dirty the inode.
                 */
                rsv_blocks = 1 + (PAGE_CACHE_SIZE >> inode->i_blkbits);
        }

        /*
         * If we have inline data and arrive here, it means that
         * we will soon create the block for the 1st page, so
         * we'd better clear the inline data here.
         */
        if (ext4_has_inline_data(inode)) {
                /* Just inode will be modified... */
                handle = ext4_journal_start(inode, EXT4_HT_INODE, 1);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        goto out_writepages;
                }
                BUG_ON(ext4_test_inode_state(inode,
                                EXT4_STATE_MAY_INLINE_DATA));
                ext4_destroy_inline_data(handle, inode);
                ext4_journal_stop(handle);
        }

        if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                range_whole = 1;

        if (wbc->range_cyclic) {
                writeback_index = mapping->writeback_index;
                if (writeback_index)
                        cycled = 0;
                mpd.first_page = writeback_index;
                mpd.last_page = -1;
        } else {
                mpd.first_page = wbc->range_start >> PAGE_CACHE_SHIFT;
                mpd.last_page = wbc->range_end >> PAGE_CACHE_SHIFT;
        }

        mpd.inode = inode;
        mpd.wbc = wbc;
        ext4_io_submit_init(&mpd.io_submit, wbc);
retry:
        if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                tag_pages_for_writeback(mapping, mpd.first_page, mpd.last_page);
        done = false;
        blk_start_plug(&plug);
        while (!done && mpd.first_page <= mpd.last_page) {
                /* For each extent of pages we use new io_end */
                mpd.io_submit.io_end = ext4_init_io_end(inode, GFP_KERNEL);
                if (!mpd.io_submit.io_end) {
                        ret = -ENOMEM;
                        break;
                }

                /*
                 * We have two constraints: We find one extent to map and we
                 * must always write out whole page (makes a difference when
                 * blocksize < pagesize) so that we don't block on IO when we
                 * try to write out the rest of the page. Journalled mode is
                 * not supported by delalloc.
                 */
                BUG_ON(ext4_should_journal_data(inode));
                needed_blocks = ext4_da_writepages_trans_blocks(inode);

                /* start a new transaction */
                handle = ext4_journal_start_with_reserve(inode,
                                EXT4_HT_WRITE_PAGE, needed_blocks, rsv_blocks);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        ext4_msg(inode->i_sb, KERN_CRIT, "%s: jbd2_start: "
                               "%ld pages, ino %lu; err %d", __func__,
                                wbc->nr_to_write, inode->i_ino, ret);
                        /* Release allocated io_end */
                        ext4_put_io_end(mpd.io_submit.io_end);
                        break;
                }

                trace_ext4_da_write_pages(inode, mpd.first_page, mpd.wbc);
                ret = mpage_prepare_extent_to_map(&mpd);
                if (!ret) {
                        if (mpd.map.m_len)
                                ret = mpage_map_and_submit_extent(handle, &mpd,
                                        &give_up_on_write);
                        else {
                                /*
                                 * We scanned the whole range (or exhausted
                                 * nr_to_write), submitted what was mapped and
                                 * didn't find anything needing mapping. We are
                                 * done.
                                 */
                                done = true;
                        }
                }
                ext4_journal_stop(handle);
                /* Submit prepared bio */
                ext4_io_submit(&mpd.io_submit);
                /* Unlock pages we didn't use */
                mpage_release_unused_pages(&mpd, give_up_on_write);
                /* Drop our io_end reference we got from init */
                ext4_put_io_end(mpd.io_submit.io_end);

                if (ret == -ENOSPC && sbi->s_journal) {
                        /*
                         * Commit the transaction which would
                         * free blocks released in the transaction
                         * and try again
                         */
                        jbd2_journal_force_commit_nested(sbi->s_journal);
                        ret = 0;
                        continue;
                }
                /* Fatal error - ENOMEM, EIO... */
                if (ret)
                        break;
        }
        blk_finish_plug(&plug);
        if (!ret && !cycled && wbc->nr_to_write > 0) {
                cycled = 1;
                mpd.last_page = writeback_index - 1;
                mpd.first_page = 0;
                goto retry;
        }

        /* Update index */
        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
                /*
                 * Set the writeback_index so that range_cyclic
                 * mode will write it back later
                 */
                mapping->writeback_index = mpd.first_page;

out_writepages:
        trace_ext4_writepages_result(inode, wbc, ret,
                                     nr_to_write - wbc->nr_to_write);
        return ret;
}

static int ext4_nonda_switch(struct super_block *sb)
{
        s64 free_clusters, dirty_clusters;
        struct ext4_sb_info *sbi = EXT4_SB(sb);

        /*
         * switch to non delalloc mode if we are running low
         * on free block. The free block accounting via percpu
         * counters can get slightly wrong with percpu_counter_batch getting
         * accumulated on each CPU without updating global counters
         * Delalloc need an accurate free block accounting. So switch
         * to non delalloc when we are near to error range.
         */
        free_clusters =
                percpu_counter_read_positive(&sbi->s_freeclusters_counter);
        dirty_clusters =
                percpu_counter_read_positive(&sbi->s_dirtyclusters_counter);
        /*
         * Start pushing delalloc when 1/2 of free blocks are dirty.
         */
        if (dirty_clusters && (free_clusters < 2 * dirty_clusters))
                try_to_writeback_inodes_sb(sb, WB_REASON_FS_FREE_SPACE);

        if (2 * free_clusters < 3 * dirty_clusters ||
            free_clusters < (dirty_clusters + EXT4_FREECLUSTERS_WATERMARK)) {
                /*
                 * free block count is less than 150% of dirty blocks
                 * or free blocks is less than watermark
                 */
                return 1;
        }
        return 0;
}

/* We always reserve for an inode update; the superblock could be there too */
static int ext4_da_write_credits(struct inode *inode, loff_t pos, unsigned len)
{
        if (likely(EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
                                EXT4_FEATURE_RO_COMPAT_LARGE_FILE)))
                return 1;

        if (pos + len <= 0x7fffffffULL)
                return 1;

        /* We might need to update the superblock to set LARGE_FILE */
        return 2;
}

static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
                               loff_t pos, unsigned len, unsigned flags,
                               struct page **pagep, void **fsdata)
{
        int ret, retries = 0;
        struct page *page;
        pgoff_t index;
        struct inode *inode = mapping->host;
        handle_t *handle;

        index = pos >> PAGE_CACHE_SHIFT;

        if (ext4_nonda_switch(inode->i_sb)) {
                *fsdata = (void *)FALL_BACK_TO_NONDELALLOC;
                return ext4_write_begin(file, mapping, pos,
                                        len, flags, pagep, fsdata);
        }
        *fsdata = (void *)0;
        trace_ext4_da_write_begin(inode, pos, len, flags);

        if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) {
                ret = ext4_da_write_inline_data_begin(mapping, inode,
                                                      pos, len, flags,
                                                      pagep, fsdata);
                if (ret < 0)
                        return ret;
                if (ret == 1)
                        return 0;
        }

        /*
         * grab_cache_page_write_begin() can take a long time if the
         * system is thrashing due to memory pressure, or if the page
         * is being written back.  So grab it first before we start
         * the transaction handle.  This also allows us to allocate
         * the page (if needed) without using GFP_NOFS.
         */
retry_grab:
        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page)
                return -ENOMEM;
        unlock_page(page);

        /*
         * With delayed allocation, we don't log the i_disksize update
         * if there is delayed block allocation. But we still need
         * to journalling the i_disksize update if writes to the end
         * of file which has an already mapped buffer.
         */
retry_journal:
        handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
                                ext4_da_write_credits(inode, pos, len));
        if (IS_ERR(handle)) {
                page_cache_release(page);
                return PTR_ERR(handle);
        }

        lock_page(page);
        if (page->mapping != mapping) {
                /* The page got truncated from under us */
                unlock_page(page);
                page_cache_release(page);
                ext4_journal_stop(handle);
                goto retry_grab;
        }
        /* In case writeback began while the page was unlocked */
        wait_for_stable_page(page);

        ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep);
        if (ret < 0) {
                unlock_page(page);
                ext4_journal_stop(handle);
                /*
                 * block_write_begin may have instantiated a few blocks
                 * outside i_size.  Trim these off again. Don't need
                 * i_size_read because we hold i_mutex.
                 */
                if (pos + len > inode->i_size)
                        ext4_truncate_failed_write(inode);

                if (ret == -ENOSPC &&
                    ext4_should_retry_alloc(inode->i_sb, &retries))
                        goto retry_journal;

                page_cache_release(page);
                return ret;
        }

        *pagep = page;
        return ret;
}

/*
 * Check if we should update i_disksize
 * when write to the end of file but not require block allocation
 */
static int ext4_da_should_update_i_disksize(struct page *page,
                                            unsigned long offset)
{
        struct buffer_head *bh;
        struct inode *inode = page->mapping->host;
        unsigned int idx;
        int i;

        bh = page_buffers(page);
        idx = offset >> inode->i_blkbits;

        for (i = 0; i < idx; i++)
                bh = bh->b_this_page;

        if (!buffer_mapped(bh) || (buffer_delay(bh)) || buffer_unwritten(bh))
                return 0;
        return 1;
}

static int ext4_da_write_end(struct file *file,
                             struct address_space *mapping,
                             loff_t pos, unsigned len, unsigned copied,
                             struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        handle_t *handle = ext4_journal_current_handle();
        loff_t new_i_size;
        unsigned long start, end;
        int write_mode = (int)(unsigned long)fsdata;

        if (write_mode == FALL_BACK_TO_NONDELALLOC)
                return ext4_write_end(file, mapping, pos,
                                      len, copied, page, fsdata);

        trace_ext4_da_write_end(inode, pos, len, copied);
        start = pos & (PAGE_CACHE_SIZE - 1);
        end = start + copied - 1;

        /*
         * generic_write_end() will run mark_inode_dirty() if i_size
         * changes.  So let's piggyback the i_disksize mark_inode_dirty
         * into that.
         */
        new_i_size = pos + copied;
        if (copied && new_i_size > EXT4_I(inode)->i_disksize) {
                if (ext4_has_inline_data(inode) ||
                    ext4_da_should_update_i_disksize(page, end)) {
                        down_write(&EXT4_I(inode)->i_data_sem);
                        if (new_i_size > EXT4_I(inode)->i_disksize)
                                EXT4_I(inode)->i_disksize = new_i_size;
                        up_write(&EXT4_I(inode)->i_data_sem);
                        /* We need to mark inode dirty even if
                         * new_i_size is less that inode->i_size
                         * bu greater than i_disksize.(hint delalloc)
                         */
                        ext4_mark_inode_dirty(handle, inode);
                }
        }

        if (write_mode != CONVERT_INLINE_DATA &&
            ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) &&
            ext4_has_inline_data(inode))
                ret2 = ext4_da_write_inline_data_end(inode, pos, len, copied,
                                                     page);
        else
                ret2 = generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);

        copied = ret2;
        if (ret2 < 0)
                ret = ret2;
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        return ret ? ret : copied;
}

static void ext4_da_invalidatepage(struct page *page, unsigned int offset,
                                   unsigned int length)
{
        /*
         * Drop reserved blocks
         */
        BUG_ON(!PageLocked(page));
        if (!page_has_buffers(page))
                goto out;

        ext4_da_page_release_reservation(page, offset, length);

out:
        ext4_invalidatepage(page, offset, length);

        return;
}

/*
 * Force all delayed allocation blocks to be allocated for a given inode.
 */
int ext4_alloc_da_blocks(struct inode *inode)
{
        trace_ext4_alloc_da_blocks(inode);

        if (!EXT4_I(inode)->i_reserved_data_blocks &&
            !EXT4_I(inode)->i_reserved_meta_blocks)
                return 0;

        /*
         * We do something simple for now.  The filemap_flush() will
         * also start triggering a write of the data blocks, which is
         * not strictly speaking necessary (and for users of
         * laptop_mode, not even desirable).  However, to do otherwise
         * would require replicating code paths in:
         *
         * ext4_writepages() ->
         *    write_cache_pages() ---> (via passed in callback function)
         *        __mpage_da_writepage() -->
         *           mpage_add_bh_to_extent()
         *           mpage_da_map_blocks()
         *
         * The problem is that write_cache_pages(), located in
         * mm/page-writeback.c, marks pages clean in preparation for
         * doing I/O, which is not desirable if we're not planning on
         * doing I/O at all.
         *
         * We could call write_cache_pages(), and then redirty all of
         * the pages by calling redirty_page_for_writepage() but that
         * would be ugly in the extreme.  So instead we would need to
         * replicate parts of the code in the above functions,
         * simplifying them because we wouldn't actually intend to
         * write out the pages, but rather only collect contiguous
         * logical block extents, call the multi-block allocator, and
         * then update the buffer heads with the block allocations.
         *
         * For now, though, we'll cheat by calling filemap_flush(),
         * which will map the blocks, and start the I/O, but not
         * actually wait for the I/O to complete.
         */
        return filemap_flush(inode->i_mapping);
}

/*
 * bmap() is special.  It gets used by applications such as lilo and by
 * the swapper to find the on-disk block of a specific piece of data.
 *
 * Naturally, this is dangerous if the block concerned is still in the
 * journal.  If somebody makes a swapfile on an ext4 data-journaling
 * filesystem and enables swap, then they may get a nasty shock when the
 * data getting swapped to that swapfile suddenly gets overwritten by
 * the original zero's written out previously to the journal and
 * awaiting writeback in the kernel's buffer cache.
 *
 * So, if we see any bmap calls here on a modified, data-journaled file,
 * take extra steps to flush any blocks which might be in the cache.
 */
static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
{
        struct inode *inode = mapping->host;
        journal_t *journal;
        int err;

        /*
         * We can get here for an inline file via the FIBMAP ioctl
         */
        if (ext4_has_inline_data(inode))
                return 0;

        if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
                        test_opt(inode->i_sb, DELALLOC)) {
                /*
                 * With delalloc we want to sync the file
                 * so that we can make sure we allocate
                 * blocks for file
                 */
                filemap_write_and_wait(mapping);
        }

        if (EXT4_JOURNAL(inode) &&
            ext4_test_inode_state(inode, EXT4_STATE_JDATA)) {
                /*
                 * This is a REALLY heavyweight approach, but the use of
                 * bmap on dirty files is expected to be extremely rare:
                 * only if we run lilo or swapon on a freshly made file
                 * do we expect this to happen.
                 *
                 * (bmap requires CAP_SYS_RAWIO so this does not
                 * represent an unprivileged user DOS attack --- we'd be
                 * in trouble if mortal users could trigger this path at
                 * will.)
                 *
                 * NB. EXT4_STATE_JDATA is not set on files other than
                 * regular files.  If somebody wants to bmap a directory
                 * or symlink and gets confused because the buffer
                 * hasn't yet been flushed to disk, they deserve
                 * everything they get.
                 */

                ext4_clear_inode_state(inode, EXT4_STATE_JDATA);
                journal = EXT4_JOURNAL(inode);
                jbd2_journal_lock_updates(journal);
                err = jbd2_journal_flush(journal);
                jbd2_journal_unlock_updates(journal);

                if (err)
                        return 0;
        }

        return generic_block_bmap(mapping, block, ext4_get_block);
}

static int ext4_readpage(struct file *file, struct page *page)
{
        int ret = -EAGAIN;
        struct inode *inode = page->mapping->host;

        trace_ext4_readpage(page);

        if (ext4_has_inline_data(inode))
                ret = ext4_readpage_inline(inode, page);

        if (ret == -EAGAIN)
                return mpage_readpage(page, ext4_get_block);

        return ret;
}

static int
ext4_readpages(struct file *file, struct address_space *mapping,
                struct list_head *pages, unsigned nr_pages)
{
        struct inode *inode = mapping->host;

        /* If the file has inline data, no need to do readpages. */
        if (ext4_has_inline_data(inode))
                return 0;

        return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
}

static void ext4_invalidatepage(struct page *page, unsigned int offset,
                                unsigned int length)
{
        trace_ext4_invalidatepage(page, offset, length);

        /* No journalling happens on data buffers when this function is used */
        WARN_ON(page_has_buffers(page) && buffer_jbd(page_buffers(page)));

        block_invalidatepage(page, offset, length);
}

static int __ext4_journalled_invalidatepage(struct page *page,
                                            unsigned int offset,
                                            unsigned int length)
{
        journal_t *journal = EXT4_JOURNAL(page->mapping->host);

        trace_ext4_journalled_invalidatepage(page, offset, length);

        /*
         * If it's a full truncate we just forget about the pending dirtying
         */
        if (offset == 0 && length == PAGE_CACHE_SIZE)
                ClearPageChecked(page);

        return jbd2_journal_invalidatepage(journal, page, offset, length);
}

/* Wrapper for aops... */
static void ext4_journalled_invalidatepage(struct page *page,
                                           unsigned int offset,
                                           unsigned int length)
{
        WARN_ON(__ext4_journalled_invalidatepage(page, offset, length) < 0);
}

static int ext4_releasepage(struct page *page, gfp_t wait)
{
        journal_t *journal = EXT4_JOURNAL(page->mapping->host);

        trace_ext4_releasepage(page);

        /* Page has dirty journalled data -> cannot release */
        if (PageChecked(page))
                return 0;
        if (journal)
                return jbd2_journal_try_to_free_buffers(journal, page, wait);
        else
                return try_to_free_buffers(page);
}

/*
 * ext4_get_block used when preparing for a DIO write or buffer write.
 * We allocate an uinitialized extent if blocks haven't been allocated.
 * The extent will be converted to initialized after the IO is complete.
 */
int ext4_get_block_write(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create)
{
        ext4_debug("ext4_get_block_write: inode %lu, create flag %d\n",
                   inode->i_ino, create);
        return _ext4_get_block(inode, iblock, bh_result,
                               EXT4_GET_BLOCKS_IO_CREATE_EXT);
}

static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
                   struct buffer_head *bh_result, int create)
{
        ext4_debug("ext4_get_block_write_nolock: inode %lu, create flag %d\n",
                   inode->i_ino, create);
        return _ext4_get_block(inode, iblock, bh_result,
                               EXT4_GET_BLOCKS_NO_LOCK);
}

static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
                            ssize_t size, void *private)
{
        ext4_io_end_t *io_end = iocb->private;

        /* if not async direct IO just return */
        if (!io_end)
                return;

        ext_debug("ext4_end_io_dio(): io_end 0x%p "
                  "for inode %lu, iocb 0x%p, offset %llu, size %zd\n",
                  iocb->private, io_end->inode->i_ino, iocb, offset,
                  size);

        iocb->private = NULL;
        io_end->offset = offset;
        io_end->size = size;
        ext4_put_io_end(io_end);
}

/*
 * For ext4 extent files, ext4 will do direct-io write to holes,
 * preallocated extents, and those write extend the file, no need to
 * fall back to buffered IO.
 *
 * For holes, we fallocate those blocks, mark them as unwritten
 * If those blocks were preallocated, we mark sure they are split, but
 * still keep the range to write as unwritten.
 *
 * The unwritten extents will be converted to written when DIO is completed.
 * For async direct IO, since the IO may still pending when return, we
 * set up an end_io call back function, which will do the conversion
 * when async direct IO completed.
 *
 * If the O_DIRECT write will extend the file then add this inode to the
 * orphan list.  So recovery will truncate it back to the original size
 * if the machine crashes during the write.
 *
 */
static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
                              struct iov_iter *iter, loff_t offset)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;
        ssize_t ret;
        size_t count = iov_iter_count(iter);
        int overwrite = 0;
        get_block_t *get_block_func = NULL;
        int dio_flags = 0;
        loff_t final_size = offset + count;
        ext4_io_end_t *io_end = NULL;

        /* Use the old path for reads and writes beyond i_size. */
        if (rw != WRITE || final_size > inode->i_size)
                return ext4_ind_direct_IO(rw, iocb, iter, offset);

        BUG_ON(iocb->private == NULL);

        /*
         * Make all waiters for direct IO properly wait also for extent
         * conversion. This also disallows race between truncate() and
         * overwrite DIO as i_dio_count needs to be incremented under i_mutex.
         */
        if (rw == WRITE)
                atomic_inc(&inode->i_dio_count);

        /* If we do a overwrite dio, i_mutex locking can be released */
        overwrite = *((int *)iocb->private);

        if (overwrite) {
                down_read(&EXT4_I(inode)->i_data_sem);
                mutex_unlock(&inode->i_mutex);
        }

        /*
         * We could direct write to holes and fallocate.
         *
         * Allocated blocks to fill the hole are marked as
         * unwritten to prevent parallel buffered read to expose
         * the stale data before DIO complete the data IO.
         *
         * As to previously fallocated extents, ext4 get_block will
         * just simply mark the buffer mapped but still keep the
         * extents unwritten.
         *
         * For non AIO case, we will convert those unwritten extents
         * to written after return back from blockdev_direct_IO.
         *
         * For async DIO, the conversion needs to be deferred when the
         * IO is completed. The ext4 end_io callback function will be
         * called to take care of the conversion work.  Here for async
         * case, we allocate an io_end structure to hook to the iocb.
         */
        iocb->private = NULL;
        if (overwrite) {
                get_block_func = ext4_get_block_write_nolock;
        } else {
                ext4_inode_aio_set(inode, NULL);
                if (!is_sync_kiocb(iocb)) {
                        io_end = ext4_init_io_end(inode, GFP_NOFS);
                        if (!io_end) {
                                ret = -ENOMEM;
                                goto retake_lock;
                        }
                        /*
                         * Grab reference for DIO. Will be dropped in
                         * ext4_end_io_dio()
                         */
                        iocb->private = ext4_get_io_end(io_end);
                        /*
                         * we save the io structure for current async direct
                         * IO, so that later ext4_map_blocks() could flag the
                         * io structure whether there is a unwritten extents
                         * needs to be converted when IO is completed.
                         */
                        ext4_inode_aio_set(inode, io_end);
                }
                get_block_func = ext4_get_block_write;
                dio_flags = DIO_LOCKING;
        }
        ret = __blockdev_direct_IO(rw, iocb, inode,
                                   inode->i_sb->s_bdev, iter,
                                   offset,
                                   get_block_func,
                                   ext4_end_io_dio,
                                   NULL,
                                   dio_flags);

        /*
         * Put our reference to io_end. This can free the io_end structure e.g.
         * in sync IO case or in case of error. It can even perform extent
         * conversion if all bios we submitted finished before we got here.
         * Note that in that case iocb->private can be already set to NULL
         * here.
         */
        if (io_end) {
                ext4_inode_aio_set(inode, NULL);
                ext4_put_io_end(io_end);
                /*
                 * When no IO was submitted ext4_end_io_dio() was not
                 * called so we have to put iocb's reference.
                 */
                if (ret <= 0 && ret != -EIOCBQUEUED && iocb->private) {
                        WARN_ON(iocb->private != io_end);
                        WARN_ON(io_end->flag & EXT4_IO_END_UNWRITTEN);
                        ext4_put_io_end(io_end);
                        iocb->private = NULL;
                }
        }
        if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
                                                EXT4_STATE_DIO_UNWRITTEN)) {
                int err;
                /*
                 * for non AIO case, since the IO is already
                 * completed, we could do the conversion right here
                 */
                err = ext4_convert_unwritten_extents(NULL, inode,
                                                     offset, ret);
                if (err < 0)
                        ret = err;
                ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
        }

retake_lock:
        if (rw == WRITE)
                inode_dio_done(inode);
        /* take i_mutex locking again if we do a ovewrite dio */
        if (overwrite) {
                up_read(&EXT4_I(inode)->i_data_sem);
                mutex_lock(&inode->i_mutex);
        }

        return ret;
}

static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
                              struct iov_iter *iter, loff_t offset)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;
        size_t count = iov_iter_count(iter);
        ssize_t ret;

        /*
         * If we are doing data journalling we don't support O_DIRECT
         */
        if (ext4_should_journal_data(inode))
                return 0;

        /* Let buffer I/O handle the inline data case. */
        if (ext4_has_inline_data(inode))
                return 0;

        trace_ext4_direct_IO_enter(inode, offset, count, rw);
        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                ret = ext4_ext_direct_IO(rw, iocb, iter, offset);
        else
                ret = ext4_ind_direct_IO(rw, iocb, iter, offset);
        trace_ext4_direct_IO_exit(inode, offset, count, rw, ret);
        return ret;
}

/*
 * Pages can be marked dirty completely asynchronously from ext4's journalling
 * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
 * much here because ->set_page_dirty is called under VFS locks.  The page is
 * not necessarily locked.
 *
 * We cannot just dirty the page and leave attached buffers clean, because the
 * buffers' dirty state is "definitive".  We cannot just set the buffers dirty
 * or jbddirty because all the journalling code will explode.
 *
 * So what we do is to mark the page "pending dirty" and next time writepage
 * is called, propagate that into the buffers appropriately.
 */
static int ext4_journalled_set_page_dirty(struct page *page)
{
        SetPageChecked(page);
        return __set_page_dirty_nobuffers(page);
}

static const struct address_space_operations ext4_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_writepage,
        .writepages             = ext4_writepages,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};

static const struct address_space_operations ext4_journalled_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_writepage,
        .writepages             = ext4_writepages,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_journalled_write_end,
        .set_page_dirty         = ext4_journalled_set_page_dirty,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_journalled_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};

static const struct address_space_operations ext4_da_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_writepage,
        .writepages             = ext4_writepages,
        .write_begin            = ext4_da_write_begin,
        .write_end              = ext4_da_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_da_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};

void ext4_set_aops(struct inode *inode)
{
        switch (ext4_inode_journal_mode(inode)) {
        case EXT4_INODE_ORDERED_DATA_MODE:
                ext4_set_inode_state(inode, EXT4_STATE_ORDERED_MODE);
                break;
        case EXT4_INODE_WRITEBACK_DATA_MODE:
                ext4_clear_inode_state(inode, EXT4_STATE_ORDERED_MODE);
                break;
        case EXT4_INODE_JOURNAL_DATA_MODE:
                inode->i_mapping->a_ops = &ext4_journalled_aops;
                return;
        default:
                BUG();
        }
        if (test_opt(inode->i_sb, DELALLOC))
                inode->i_mapping->a_ops = &ext4_da_aops;
        else
                inode->i_mapping->a_ops = &ext4_aops;
}

/*
 * ext4_block_zero_page_range() zeros out a mapping of length 'length'
 * starting from file offset 'from'.  The range to be zero'd must
 * be contained with in one block.  If the specified range exceeds
 * the end of the block it will be shortened to end of the block
 * that cooresponds to 'from'
 */
static int ext4_block_zero_page_range(handle_t *handle,
                struct address_space *mapping, loff_t from, loff_t length)
{
        ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
        unsigned offset = from & (PAGE_CACHE_SIZE-1);
        unsigned blocksize, max, pos;
        ext4_lblk_t iblock;
        struct inode *inode = mapping->host;
        struct buffer_head *bh;
        struct page *page;
        int err = 0;

        page = find_or_create_page(mapping, from >> PAGE_CACHE_SHIFT,
                                   mapping_gfp_mask(mapping) & ~__GFP_FS);
        if (!page)
                return -ENOMEM;

        blocksize = inode->i_sb->s_blocksize;
        max = blocksize - (offset & (blocksize - 1));

        /*
         * correct length if it does not fall between
         * 'from' and the end of the block
         */
        if (length > max || length < 0)
                length = max;

        iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);

        if (!page_has_buffers(page))
                create_empty_buffers(page, blocksize, 0);

        /* Find the buffer that contains "offset" */
        bh = page_buffers(page);
        pos = blocksize;
        while (offset >= pos) {
                bh = bh->b_this_page;
                iblock++;
                pos += blocksize;
        }
        if (buffer_freed(bh)) {
                BUFFER_TRACE(bh, "freed: skip");
                goto unlock;
        }
        if (!buffer_mapped(bh)) {
                BUFFER_TRACE(bh, "unmapped");
                ext4_get_block(inode, iblock, bh, 0);
                /* unmapped? It's a hole - nothing to do */
                if (!buffer_mapped(bh)) {
                        BUFFER_TRACE(bh, "still unmapped");
                        goto unlock;
                }
        }

        /* Ok, it's mapped. Make sure it's up-to-date */
        if (PageUptodate(page))
                set_buffer_uptodate(bh);

        if (!buffer_uptodate(bh)) {
                err = -EIO;
                ll_rw_block(READ, 1, &bh);
                wait_on_buffer(bh);
                /* Uhhuh. Read error. Complain and punt. */
                if (!buffer_uptodate(bh))
                        goto unlock;
        }
        if (ext4_should_journal_data(inode)) {
                BUFFER_TRACE(bh, "get write access");
                err = ext4_journal_get_write_access(handle, bh);
                if (err)
                        goto unlock;
        }
        zero_user(page, offset, length);
        BUFFER_TRACE(bh, "zeroed end of block");

        if (ext4_should_journal_data(inode)) {
                err = ext4_handle_dirty_metadata(handle, inode, bh);
        } else {
                err = 0;
                mark_buffer_dirty(bh);
                if (ext4_test_inode_state(inode, EXT4_STATE_ORDERED_MODE))
                        err = ext4_jbd2_file_inode(handle, inode);
        }

unlock:
        unlock_page(page);
        page_cache_release(page);
        return err;
}

/*
 * ext4_block_truncate_page() zeroes out a mapping from file offset `from'
 * up to the end of the block which corresponds to `from'.
 * This required during truncate. We need to physically zero the tail end
 * of that block so it doesn't yield old data if the file is later grown.
 */
static int ext4_block_truncate_page(handle_t *handle,
                struct address_space *mapping, loff_t from)
{
        unsigned offset = from & (PAGE_CACHE_SIZE-1);
        unsigned length;
        unsigned blocksize;
        struct inode *inode = mapping->host;

        blocksize = inode->i_sb->s_blocksize;
        length = blocksize - (offset & (blocksize - 1));

        return ext4_block_zero_page_range(handle, mapping, from, length);
}

int ext4_zero_partial_blocks(handle_t *handle, struct inode *inode,
                             loff_t lstart, loff_t length)
{
        struct super_block *sb = inode->i_sb;
        struct address_space *mapping = inode->i_mapping;
        unsigned partial_start, partial_end;
        ext4_fsblk_t start, end;
        loff_t byte_end = (lstart + length - 1);
        int err = 0;

        partial_start = lstart & (sb->s_blocksize - 1);
        partial_end = byte_end & (sb->s_blocksize - 1);

        start = lstart >> sb->s_blocksize_bits;
        end = byte_end >> sb->s_blocksize_bits;

        /* Handle partial zero within the single block */
        if (start == end &&
            (partial_start || (partial_end != sb->s_blocksize - 1))) {
                err = ext4_block_zero_page_range(handle, mapping,
                                                 lstart, length);
                return err;
        }
        /* Handle partial zero out on the start of the range */
        if (partial_start) {
                err = ext4_block_zero_page_range(handle, mapping,
                                                 lstart, sb->s_blocksize);
                if (err)
                        return err;
        }
        /* Handle partial zero out on the end of the range */
        if (partial_end != sb->s_blocksize - 1)
                err = ext4_block_zero_page_range(handle, mapping,
                                                 byte_end - partial_end,
                                                 partial_end + 1);
        return err;
}

int ext4_can_truncate(struct inode *inode)
{
        if (S_ISREG(inode->i_mode))
                return 1;
        if (S_ISDIR(inode->i_mode))
                return 1;
        if (S_ISLNK(inode->i_mode))
                return !ext4_inode_is_fast_symlink(inode);
        return 0;
}

/*
 * ext4_punch_hole: punches a hole in a file by releaseing the blocks
 * associated with the given offset and length
 *
 * @inode:  File inode
 * @offset: The offset where the hole will begin
 * @len:    The length of the hole
 *
 * Returns: 0 on success or negative on failure
 */

int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
{
        struct super_block *sb = inode->i_sb;
        ext4_lblk_t first_block, stop_block;
        struct address_space *mapping = inode->i_mapping;
        loff_t first_block_offset, last_block_offset;
        handle_t *handle;
        unsigned int credits;
        int ret = 0;

        if (!S_ISREG(inode->i_mode))
                return -EOPNOTSUPP;

        trace_ext4_punch_hole(inode, offset, length, 0);

        /*
         * Write out all dirty pages to avoid race conditions
         * Then release them.
         */
        if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
                ret = filemap_write_and_wait_range(mapping, offset,
                                                   offset + length - 1);
                if (ret)
                        return ret;
        }

        mutex_lock(&inode->i_mutex);

        /* No need to punch hole beyond i_size */
        if (offset >= inode->i_size)
                goto out_mutex;

        /*
         * If the hole extends beyond i_size, set the hole
         * to end after the page that contains i_size
         */
        if (offset + length > inode->i_size) {
                length = inode->i_size +
                   PAGE_CACHE_SIZE - (inode->i_size & (PAGE_CACHE_SIZE - 1)) -
                   offset;
        }

        if (offset & (sb->s_blocksize - 1) ||
            (offset + length) & (sb->s_blocksize - 1)) {
                /*
                 * Attach jinode to inode for jbd2 if we do any zeroing of
                 * partial block
                 */
                ret = ext4_inode_attach_jinode(inode);
                if (ret < 0)
                        goto out_mutex;

        }

        first_block_offset = round_up(offset, sb->s_blocksize);
        last_block_offset = round_down((offset + length), sb->s_blocksize) - 1;

        /* Now release the pages and zero block aligned part of pages*/
        if (last_block_offset > first_block_offset)
                truncate_pagecache_range(inode, first_block_offset,
                                         last_block_offset);

        /* Wait all existing dio workers, newcomers will block on i_mutex */
        ext4_inode_block_unlocked_dio(inode);
        inode_dio_wait(inode);

        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                credits = ext4_writepage_trans_blocks(inode);
        else
                credits = ext4_blocks_for_truncate(inode);
        handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, credits);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                ext4_std_error(sb, ret);
                goto out_dio;
        }

        ret = ext4_zero_partial_blocks(handle, inode, offset,
                                       length);
        if (ret)
                goto out_stop;

        first_block = (offset + sb->s_blocksize - 1) >>
                EXT4_BLOCK_SIZE_BITS(sb);
        stop_block = (offset + length) >> EXT4_BLOCK_SIZE_BITS(sb);

        /* If there are no blocks to remove, return now */
        if (first_block >= stop_block)
                goto out_stop;

        down_write(&EXT4_I(inode)->i_data_sem);
        ext4_discard_preallocations(inode);

        ret = ext4_es_remove_extent(inode, first_block,
                                    stop_block - first_block);
        if (ret) {
                up_write(&EXT4_I(inode)->i_data_sem);
                goto out_stop;
        }

        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                ret = ext4_ext_remove_space(inode, first_block,
                                            stop_block - 1);
        else
                ret = ext4_ind_remove_space(handle, inode, first_block,
                                            stop_block);

        up_write(&EXT4_I(inode)->i_data_sem);
        if (IS_SYNC(inode))
                ext4_handle_sync(handle);

        /* Now release the pages again to reduce race window */
        if (last_block_offset > first_block_offset)
                truncate_pagecache_range(inode, first_block_offset,
                                         last_block_offset);

        inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
        ext4_mark_inode_dirty(handle, inode);
out_stop:
        ext4_journal_stop(handle);
out_dio:
        ext4_inode_resume_unlocked_dio(inode);
out_mutex:
        mutex_unlock(&inode->i_mutex);
        return ret;
}

int ext4_inode_attach_jinode(struct inode *inode)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct jbd2_inode *jinode;

        if (ei->jinode || !EXT4_SB(inode->i_sb)->s_journal)
                return 0;

        jinode = jbd2_alloc_inode(GFP_KERNEL);
        spin_lock(&inode->i_lock);
        if (!ei->jinode) {
                if (!jinode) {
                        spin_unlock(&inode->i_lock);
                        return -ENOMEM;
                }
                ei->jinode = jinode;
                jbd2_journal_init_jbd_inode(ei->jinode, inode);
                jinode = NULL;
        }
        spin_unlock(&inode->i_lock);
        if (unlikely(jinode != NULL))
                jbd2_free_inode(jinode);
        return 0;
}

/*
 * ext4_truncate()
 *
 * We block out ext4_get_block() block instantiations across the entire
 * transaction, and VFS/VM ensures that ext4_truncate() cannot run
 * simultaneously on behalf of the same inode.
 *
 * As we work through the truncate and commit bits of it to the journal there
 * is one core, guiding principle: the file's tree must always be consistent on
 * disk.  We must be able to restart the truncate after a crash.
 *
 * The file's tree may be transiently inconsistent in memory (although it
 * probably isn't), but whenever we close off and commit a journal transaction,
 * the contents of (the filesystem + the journal) must be consistent and
 * restartable.  It's pretty simple, really: bottom up, right to left (although
 * left-to-right works OK too).
 *
 * Note that at recovery time, journal replay occurs *before* the restart of
 * truncate against the orphan inode list.
 *
 * The committed inode has the new, desired i_size (which is the same as
 * i_disksize in this case).  After a crash, ext4_orphan_cleanup() will see
 * that this inode's truncate did not complete and it will again call
 * ext4_truncate() to have another go.  So there will be instantiated blocks
 * to the right of the truncation point in a crashed ext4 filesystem.  But
 * that's fine - as long as they are linked from the inode, the post-crash
 * ext4_truncate() run will find them and release them.
 */
void ext4_truncate(struct inode *inode)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        unsigned int credits;
        handle_t *handle;
        struct address_space *mapping = inode->i_mapping;

        /*
         * There is a possibility that we're either freeing the inode
         * or it's a completely new inode. In those cases we might not
         * have i_mutex locked because it's not necessary.
         */
        if (!(inode->i_state & (I_NEW|I_FREEING)))
                WARN_ON(!mutex_is_locked(&inode->i_mutex));
        trace_ext4_truncate_enter(inode);

        if (!ext4_can_truncate(inode))
                return;

        ext4_clear_inode_flag(inode, EXT4_INODE_EOFBLOCKS);

        if (inode->i_size == 0 && !test_opt(inode->i_sb, NO_AUTO_DA_ALLOC))
                ext4_set_inode_state(inode, EXT4_STATE_DA_ALLOC_CLOSE);

        if (ext4_has_inline_data(inode)) {
                int has_inline = 1;

                ext4_inline_data_truncate(inode, &has_inline);
                if (has_inline)
                        return;
        }

        /* If we zero-out tail of the page, we have to create jinode for jbd2 */
        if (inode->i_size & (inode->i_sb->s_blocksize - 1)) {
                if (ext4_inode_attach_jinode(inode) < 0)
                        return;
        }

        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                credits = ext4_writepage_trans_blocks(inode);
        else
                credits = ext4_blocks_for_truncate(inode);

        handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, credits);
        if (IS_ERR(handle)) {
                ext4_std_error(inode->i_sb, PTR_ERR(handle));
                return;
        }

        if (inode->i_size & (inode->i_sb->s_blocksize - 1))
                ext4_block_truncate_page(handle, mapping, inode->i_size);

        /*
         * We add the inode to the orphan list, so that if this
         * truncate spans multiple transactions, and we crash, we will
         * resume the truncate when the filesystem recovers.  It also
         * marks the inode dirty, to catch the new size.
         *
         * Implication: the file must always be in a sane, consistent
         * truncatable state while each transaction commits.
         */
        if (ext4_orphan_add(handle, inode))
                goto out_stop;

        down_write(&EXT4_I(inode)->i_data_sem);

        ext4_discard_preallocations(inode);

        if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                ext4_ext_truncate(handle, inode);
        else
                ext4_ind_truncate(handle, inode);

        up_write(&ei->i_data_sem);

        if (IS_SYNC(inode))
                ext4_handle_sync(handle);

out_stop:
        /*
         * If this was a simple ftruncate() and the file will remain alive,
         * then we need to clear up the orphan record which we created above.
         * However, if this was a real unlink then we were called by
         * ext4_delete_inode(), and we allow that function to clean up the
         * orphan info for us.
         */
        if (inode->i_nlink)
                ext4_orphan_del(handle, inode);

        inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
        ext4_mark_inode_dirty(handle, inode);
        ext4_journal_stop(handle);

        trace_ext4_truncate_exit(inode);
}

/*
 * ext4_get_inode_loc returns with an extra refcount against the inode's
 * underlying buffer_head on success. If 'in_mem' is true, we have all
 * data in memory that is needed to recreate the on-disk version of this
 * inode.
 */
static int __ext4_get_inode_loc(struct inode *inode,
                                struct ext4_iloc *iloc, int in_mem)
{
        struct ext4_group_desc  *gdp;
        struct buffer_head      *bh;
        struct super_block      *sb = inode->i_sb;
        ext4_fsblk_t            block;
        int                     inodes_per_block, inode_offset;

        iloc->bh = NULL;
        if (!ext4_valid_inum(sb, inode->i_ino))
                return -EIO;

        iloc->block_group = (inode->i_ino - 1) / EXT4_INODES_PER_GROUP(sb);
        gdp = ext4_get_group_desc(sb, iloc->block_group, NULL);
        if (!gdp)
                return -EIO;

        /*
         * Figure out the offset within the block group inode table
         */
        inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
        inode_offset = ((inode->i_ino - 1) %
                        EXT4_INODES_PER_GROUP(sb));
        block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
        iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);

        bh = sb_getblk(sb, block);
        if (unlikely(!bh))
                return -ENOMEM;
        if (!buffer_uptodate(bh)) {
                lock_buffer(bh);

                /*
                 * If the buffer has the write error flag, we have failed
                 * to write out another inode in the same block.  In this
                 * case, we don't have to read the block because we may
                 * read the old inode data successfully.
                 */
                if (buffer_write_io_error(bh) && !buffer_uptodate(bh))
                        set_buffer_uptodate(bh);

                if (buffer_uptodate(bh)) {
                        /* someone brought it uptodate while we waited */
                        unlock_buffer(bh);
                        goto has_buffer;
                }

                /*
                 * If we have all information of the inode in memory and this
                 * is the only valid inode in the block, we need not read the
                 * block.
                 */
                if (in_mem) {
                        struct buffer_head *bitmap_bh;
                        int i, start;

                        start = inode_offset & ~(inodes_per_block - 1);

                        /* Is the inode bitmap in cache? */
                        bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
                        if (unlikely(!bitmap_bh))
                                goto make_io;

                        /*
                         * If the inode bitmap isn't in cache then the
                         * optimisation may end up performing two reads instead
                         * of one, so skip it.
                         */
                        if (!buffer_uptodate(bitmap_bh)) {
                                brelse(bitmap_bh);
                                goto make_io;
                        }
                        for (i = start; i < start + inodes_per_block; i++) {
                                if (i == inode_offset)
                                        continue;
                                if (ext4_test_bit(i, bitmap_bh->b_data))
                                        break;
                        }
                        brelse(bitmap_bh);
                        if (i == start + inodes_per_block) {
                                /* all other inodes are free, so skip I/O */
                                memset(bh->b_data, 0, bh->b_size);
                                set_buffer_uptodate(bh);
                                unlock_buffer(bh);
                                goto has_buffer;
                        }
                }

make_io:
                /*
                 * If we need to do any I/O, try to pre-readahead extra
                 * blocks from the inode table.
                 */
                if (EXT4_SB(sb)->s_inode_readahead_blks) {
                        ext4_fsblk_t b, end, table;
                        unsigned num;
                        __u32 ra_blks = EXT4_SB(sb)->s_inode_readahead_blks;

                        table = ext4_inode_table(sb, gdp);
                        /* s_inode_readahead_blks is always a power of 2 */
                        b = block & ~((ext4_fsblk_t) ra_blks - 1);
                        if (table > b)
                                b = table;
                        end = b + ra_blks;
                        num = EXT4_INODES_PER_GROUP(sb);
                        if (ext4_has_group_desc_csum(sb))
                                num -= ext4_itable_unused_count(sb, gdp);
                        table += num / inodes_per_block;
                        if (end > table)
                                end = table;
                        while (b <= end)
                                sb_breadahead(sb, b++);
                }

                /*
                 * There are other valid inodes in the buffer, this inode
                 * has in-inode xattrs, or we don't have this inode in memory.
                 * Read the block from disk.
                 */
                trace_ext4_load_inode(inode);
                get_bh(bh);
                bh->b_end_io = end_buffer_read_sync;
                submit_bh(READ | REQ_META | REQ_PRIO, bh);
                wait_on_buffer(bh);
                if (!buffer_uptodate(bh)) {
                        EXT4_ERROR_INODE_BLOCK(inode, block,
                                               "unable to read itable block");
                        brelse(bh);
                        return -EIO;
                }
        }
has_buffer:
        iloc->bh = bh;
        return 0;
}

int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
{
        /* We have all inode data except xattrs in memory here. */
        return __ext4_get_inode_loc(inode, iloc,
                !ext4_test_inode_state(inode, EXT4_STATE_XATTR));
}

void ext4_set_inode_flags(struct inode *inode)
{
        unsigned int flags = EXT4_I(inode)->i_flags;
        unsigned int new_fl = 0;

        if (flags & EXT4_SYNC_FL)
                new_fl |= S_SYNC;
        if (flags & EXT4_APPEND_FL)
                new_fl |= S_APPEND;
        if (flags & EXT4_IMMUTABLE_FL)
                new_fl |= S_IMMUTABLE;
        if (flags & EXT4_NOATIME_FL)
                new_fl |= S_NOATIME;
        if (flags & EXT4_DIRSYNC_FL)
                new_fl |= S_DIRSYNC;
        inode_set_flags(inode, new_fl,
                        S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
}

/* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
void ext4_get_inode_flags(struct ext4_inode_info *ei)
{
        unsigned int vfs_fl;
        unsigned long old_fl, new_fl;

        do {
                vfs_fl = ei->vfs_inode.i_flags;
                old_fl = ei->i_flags;
                new_fl = old_fl & ~(EXT4_SYNC_FL|EXT4_APPEND_FL|
                                EXT4_IMMUTABLE_FL|EXT4_NOATIME_FL|
                                EXT4_DIRSYNC_FL);
                if (vfs_fl & S_SYNC)
                        new_fl |= EXT4_SYNC_FL;
                if (vfs_fl & S_APPEND)
                        new_fl |= EXT4_APPEND_FL;
                if (vfs_fl & S_IMMUTABLE)
                        new_fl |= EXT4_IMMUTABLE_FL;
                if (vfs_fl & S_NOATIME)
                        new_fl |= EXT4_NOATIME_FL;
                if (vfs_fl & S_DIRSYNC)
                        new_fl |= EXT4_DIRSYNC_FL;
        } while (cmpxchg(&ei->i_flags, old_fl, new_fl) != old_fl);
}

static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
                                  struct ext4_inode_info *ei)
{
        blkcnt_t i_blocks ;
        struct inode *inode = &(ei->vfs_inode);
        struct super_block *sb = inode->i_sb;

        if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                EXT4_FEATURE_RO_COMPAT_HUGE_FILE)) {
                /* we are using combined 48 bit field */
                i_blocks = ((u64)le16_to_cpu(raw_inode->i_blocks_high)) << 32 |
                                        le32_to_cpu(raw_inode->i_blocks_lo);
                if (ext4_test_inode_flag(inode, EXT4_INODE_HUGE_FILE)) {
                        /* i_blocks represent file system block size */
                        return i_blocks  << (inode->i_blkbits - 9);
                } else {
                        return i_blocks;
                }
        } else {
                return le32_to_cpu(raw_inode->i_blocks_lo);
        }
}

static inline void ext4_iget_extra_inode(struct inode *inode,
                                         struct ext4_inode *raw_inode,
                                         struct ext4_inode_info *ei)
{
        __le32 *magic = (void *)raw_inode +
                        EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize;
        if (*magic == cpu_to_le32(EXT4_XATTR_MAGIC)) {
                ext4_set_inode_state(inode, EXT4_STATE_XATTR);
                ext4_find_inline_data_nolock(inode);
        } else
                EXT4_I(inode)->i_inline_off = 0;
}

struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
{
        struct ext4_iloc iloc;
        struct ext4_inode *raw_inode;
        struct ext4_inode_info *ei;
        struct inode *inode;
        journal_t *journal = EXT4_SB(sb)->s_journal;
        long ret;
        int block;
        uid_t i_uid;
        gid_t i_gid;

        inode = iget_locked(sb, ino);
        if (!inode)
                return ERR_PTR(-ENOMEM);
        if (!(inode->i_state & I_NEW))
                return inode;

        ei = EXT4_I(inode);
        iloc.bh = NULL;

        ret = __ext4_get_inode_loc(inode, &iloc, 0);
        if (ret < 0)
                goto bad_inode;
        raw_inode = ext4_raw_inode(&iloc);

        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
                if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
                    EXT4_INODE_SIZE(inode->i_sb)) {
                        EXT4_ERROR_INODE(inode, "bad extra_isize (%u != %u)",
                                EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize,
                                EXT4_INODE_SIZE(inode->i_sb));
                        ret = -EIO;
                        goto bad_inode;
                }
        } else
                ei->i_extra_isize = 0;

        /* Precompute checksum seed for inode metadata */
        if (ext4_has_metadata_csum(sb)) {
                struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
                __u32 csum;
                __le32 inum = cpu_to_le32(inode->i_ino);
                __le32 gen = raw_inode->i_generation;
                csum = ext4_chksum(sbi, sbi->s_csum_seed, (__u8 *)&inum,
                                   sizeof(inum));
                ei->i_csum_seed = ext4_chksum(sbi, csum, (__u8 *)&gen,
                                              sizeof(gen));
        }

        if (!ext4_inode_csum_verify(inode, raw_inode, ei)) {
                EXT4_ERROR_INODE(inode, "checksum invalid");
                ret = -EIO;
                goto bad_inode;
        }

        inode->i_mode = le16_to_cpu(raw_inode->i_mode);
        i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
        i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
        if (!(test_opt(inode->i_sb, NO_UID32))) {
                i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
                i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
        }
        i_uid_write(inode, i_uid);
        i_gid_write(inode, i_gid);
        set_nlink(inode, le16_to_cpu(raw_inode->i_links_count));

        ext4_clear_state_flags(ei);     /* Only relevant on 32-bit archs */
        ei->i_inline_off = 0;
        ei->i_dir_start_lookup = 0;
        ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
        /* We now have enough fields to check if the inode was active or not.
         * This is needed because nfsd might try to access dead inodes
         * the test is that same one that e2fsck uses
         * NeilBrown 1999oct15
         */
        if (inode->i_nlink == 0) {
                if ((inode->i_mode == 0 ||
                     !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) &&
                    ino != EXT4_BOOT_LOADER_INO) {
                        /* this inode is deleted */
                        ret = -ESTALE;
                        goto bad_inode;
                }
                /* The only unlinked inodes we let through here have
                 * valid i_mode and are being read by the orphan
                 * recovery code: that's fine, we're about to complete
                 * the process of deleting those.
                 * OR it is the EXT4_BOOT_LOADER_INO which is
                 * not initialized on a new filesystem. */
        }
        ei->i_flags = le32_to_cpu(raw_inode->i_flags);
        inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
        ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
        if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_64BIT))
                ei->i_file_acl |=
                        ((__u64)le16_to_cpu(raw_inode->i_file_acl_high)) << 32;
        inode->i_size = ext4_isize(raw_inode);
        ei->i_disksize = inode->i_size;
#ifdef CONFIG_QUOTA
        ei->i_reserved_quota = 0;
#endif
        inode->i_generation = le32_to_cpu(raw_inode->i_generation);
        ei->i_block_group = iloc.block_group;
        ei->i_last_alloc_group = ~0;
        /*
         * NOTE! The in-memory inode i_data array is in little-endian order
         * even on big-endian machines: we do NOT byteswap the block numbers!
         */
        for (block = 0; block < EXT4_N_BLOCKS; block++)
                ei->i_data[block] = raw_inode->i_block[block];
        INIT_LIST_HEAD(&ei->i_orphan);

        /*
         * Set transaction id's of transactions that have to be committed
         * to finish f[data]sync. We set them to currently running transaction
         * as we cannot be sure that the inode or some of its metadata isn't
         * part of the transaction - the inode could have been reclaimed and
         * now it is reread from disk.
         */
        if (journal) {
                transaction_t *transaction;
                tid_t tid;

                read_lock(&journal->j_state_lock);
                if (journal->j_running_transaction)
                        transaction = journal->j_running_transaction;
                else
                        transaction = journal->j_committing_transaction;
                if (transaction)
                        tid = transaction->t_tid;
                else
                        tid = journal->j_commit_sequence;
                read_unlock(&journal->j_state_lock);
                ei->i_sync_tid = tid;
                ei->i_datasync_tid = tid;
        }

        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                if (ei->i_extra_isize == 0) {
                        /* The extra space is currently unused. Use it. */
                        ei->i_extra_isize = sizeof(struct ext4_inode) -
                                            EXT4_GOOD_OLD_INODE_SIZE;
                } else {
                        ext4_iget_extra_inode(inode, raw_inode, ei);
                }
        }

        EXT4_INODE_GET_XTIME(i_ctime, inode, raw_inode);
        EXT4_INODE_GET_XTIME(i_mtime, inode, raw_inode);
        EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
        EXT4_EINODE_GET_XTIME(i_crtime, ei, raw_inode);

        if (likely(!test_opt2(inode->i_sb, HURD_COMPAT))) {
                inode->i_version = le32_to_cpu(raw_inode->i_disk_version);
                if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                        if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                                inode->i_version |=
                    (__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
                }
        }

        ret = 0;
        if (ei->i_file_acl &&
            !ext4_data_block_valid(EXT4_SB(sb), ei->i_file_acl, 1)) {
                EXT4_ERROR_INODE(inode, "bad extended attribute block %llu",
                                 ei->i_file_acl);
                ret = -EIO;
                goto bad_inode;
        } else if (!ext4_has_inline_data(inode)) {
                if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
                        if ((S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
                            (S_ISLNK(inode->i_mode) &&
                             !ext4_inode_is_fast_symlink(inode))))
                                /* Validate extent which is part of inode */
                                ret = ext4_ext_check_inode(inode);
                } else if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
                           (S_ISLNK(inode->i_mode) &&
                            !ext4_inode_is_fast_symlink(inode))) {
                        /* Validate block references which are part of inode */
                        ret = ext4_ind_check_inode(inode);
                }
        }
        if (ret)
                goto bad_inode;

        if (S_ISREG(inode->i_mode)) {
                inode->i_op = &ext4_file_inode_operations;
                inode->i_fop = &ext4_file_operations;
                ext4_set_aops(inode);
        } else if (S_ISDIR(inode->i_mode)) {
                inode->i_op = &ext4_dir_inode_operations;
                inode->i_fop = &ext4_dir_operations;
        } else if (S_ISLNK(inode->i_mode)) {
                if (ext4_inode_is_fast_symlink(inode)) {
                        inode->i_op = &ext4_fast_symlink_inode_operations;
                        nd_terminate_link(ei->i_data, inode->i_size,
                                sizeof(ei->i_data) - 1);
                } else {
                        inode->i_op = &ext4_symlink_inode_operations;
                        ext4_set_aops(inode);
                }
        } else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
              S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
                inode->i_op = &ext4_special_inode_operations;
                if (raw_inode->i_block[0])
                        init_special_inode(inode, inode->i_mode,
                           old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
                else
                        init_special_inode(inode, inode->i_mode,
                           new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
        } else if (ino == EXT4_BOOT_LOADER_INO) {
                make_bad_inode(inode);
        } else {
                ret = -EIO;
                EXT4_ERROR_INODE(inode, "bogus i_mode (%o)", inode->i_mode);
                goto bad_inode;
        }
        brelse(iloc.bh);
        ext4_set_inode_flags(inode);
        unlock_new_inode(inode);
        return inode;

bad_inode:
        brelse(iloc.bh);
        iget_failed(inode);
        return ERR_PTR(ret);
}

struct inode *ext4_iget_normal(struct super_block *sb, unsigned long ino)
{
        if (ino < EXT4_FIRST_INO(sb) && ino != EXT4_ROOT_INO)
                return ERR_PTR(-EIO);
        return ext4_iget(sb, ino);
}

static int ext4_inode_blocks_set(handle_t *handle,
                                struct ext4_inode *raw_inode,
                                struct ext4_inode_info *ei)
{
        struct inode *inode = &(ei->vfs_inode);
        u64 i_blocks = inode->i_blocks;
        struct super_block *sb = inode->i_sb;

        if (i_blocks <= ~0U) {
                /*
                 * i_blocks can be represented in a 32 bit variable
                 * as multiple of 512 bytes
                 */
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = 0;
                ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
                return 0;
        }
        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_HUGE_FILE))
                return -EFBIG;

        if (i_blocks <= 0xffffffffffffULL) {
                /*
                 * i_blocks can be represented in a 48 bit variable
                 * as multiple of 512 bytes
                 */
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
                ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
        } else {
                ext4_set_inode_flag(inode, EXT4_INODE_HUGE_FILE);
                /* i_block is stored in file system block size */
                i_blocks = i_blocks >> (inode->i_blkbits - 9);
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
        }
        return 0;
}

/*
 * Post the struct inode info into an on-disk inode location in the
 * buffer-cache.  This gobbles the caller's reference to the
 * buffer_head in the inode location struct.
 *
 * The caller must have write access to iloc->bh.
 */
static int ext4_do_update_inode(handle_t *handle,
                                struct inode *inode,
                                struct ext4_iloc *iloc)
{
        struct ext4_inode *raw_inode = ext4_raw_inode(iloc);
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct buffer_head *bh = iloc->bh;
        struct super_block *sb = inode->i_sb;
        int err = 0, rc, block;
        int need_datasync = 0, set_large_file = 0;
        uid_t i_uid;
        gid_t i_gid;

        spin_lock(&ei->i_raw_lock);

        /* For fields not tracked in the in-memory inode,
         * initialise them to zero for new inodes. */
        if (ext4_test_inode_state(inode, EXT4_STATE_NEW))
                memset(raw_inode, 0, EXT4_SB(inode->i_sb)->s_inode_size);

        ext4_get_inode_flags(ei);
        raw_inode->i_mode = cpu_to_le16(inode->i_mode);
        i_uid = i_uid_read(inode);
        i_gid = i_gid_read(inode);
        if (!(test_opt(inode->i_sb, NO_UID32))) {
                raw_inode->i_uid_low = cpu_to_le16(low_16_bits(i_uid));
                raw_inode->i_gid_low = cpu_to_le16(low_16_bits(i_gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
                if (!ei->i_dtime) {
                        raw_inode->i_uid_high =
                                cpu_to_le16(high_16_bits(i_uid));
                        raw_inode->i_gid_high =
                                cpu_to_le16(high_16_bits(i_gid));
                } else {
                        raw_inode->i_uid_high = 0;
                        raw_inode->i_gid_high = 0;
                }
        } else {
                raw_inode->i_uid_low = cpu_to_le16(fs_high2lowuid(i_uid));
                raw_inode->i_gid_low = cpu_to_le16(fs_high2lowgid(i_gid));
                raw_inode->i_uid_high = 0;
                raw_inode->i_gid_high = 0;
        }
        raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);

        EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
        EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
        EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
        EXT4_EINODE_SET_XTIME(i_crtime, ei, raw_inode);

        if (ext4_inode_blocks_set(handle, raw_inode, ei)) {
                spin_unlock(&ei->i_raw_lock);
                goto out_brelse;
        }
        raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
        raw_inode->i_flags = cpu_to_le32(ei->i_flags & 0xFFFFFFFF);
        if (likely(!test_opt2(inode->i_sb, HURD_COMPAT)))
                raw_inode->i_file_acl_high =
                        cpu_to_le16(ei->i_file_acl >> 32);
        raw_inode->i_file_acl_lo = cpu_to_le32(ei->i_file_acl);
        if (ei->i_disksize != ext4_isize(raw_inode)) {
                ext4_isize_set(raw_inode, ei->i_disksize);
                need_datasync = 1;
        }
        if (ei->i_disksize > 0x7fffffffULL) {
                if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                EXT4_FEATURE_RO_COMPAT_LARGE_FILE) ||
                                EXT4_SB(sb)->s_es->s_rev_level ==
                    cpu_to_le32(EXT4_GOOD_OLD_REV))
                        set_large_file = 1;
        }
        raw_inode->i_generation = cpu_to_le32(inode->i_generation);
        if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
                if (old_valid_dev(inode->i_rdev)) {
                        raw_inode->i_block[0] =
                                cpu_to_le32(old_encode_dev(inode->i_rdev));
                        raw_inode->i_block[1] = 0;
                } else {
                        raw_inode->i_block[0] = 0;
                        raw_inode->i_block[1] =
                                cpu_to_le32(new_encode_dev(inode->i_rdev));
                        raw_inode->i_block[2] = 0;
                }
        } else if (!ext4_has_inline_data(inode)) {
                for (block = 0; block < EXT4_N_BLOCKS; block++)
                        raw_inode->i_block[block] = ei->i_data[block];
        }

        if (likely(!test_opt2(inode->i_sb, HURD_COMPAT))) {
                raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
                if (ei->i_extra_isize) {
                        if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                                raw_inode->i_version_hi =
                                        cpu_to_le32(inode->i_version >> 32);
                        raw_inode->i_extra_isize =
                                cpu_to_le16(ei->i_extra_isize);
                }
        }

        ext4_inode_csum_set(inode, raw_inode, ei);

        spin_unlock(&ei->i_raw_lock);

        BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
        rc = ext4_handle_dirty_metadata(handle, NULL, bh);
        if (!err)
                err = rc;
        ext4_clear_inode_state(inode, EXT4_STATE_NEW);
        if (set_large_file) {
                BUFFER_TRACE(EXT4_SB(sb)->s_sbh, "get write access");
                err = ext4_journal_get_write_access(handle, EXT4_SB(sb)->s_sbh);
                if (err)
                        goto out_brelse;
                ext4_update_dynamic_rev(sb);
                EXT4_SET_RO_COMPAT_FEATURE(sb,
                                           EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
                ext4_handle_sync(handle);
                err = ext4_handle_dirty_super(handle, sb);
        }
        ext4_update_inode_fsync_trans(handle, inode, need_datasync);
out_brelse:
        brelse(bh);
        ext4_std_error(inode->i_sb, err);
        return err;
}

/*
 * ext4_write_inode()
 *
 * We are called from a few places:
 *
 * - Within generic_file_aio_write() -> generic_write_sync() for O_SYNC files.
 *   Here, there will be no transaction running. We wait for any running
 *   transaction to commit.
 *
 * - Within flush work (sys_sync(), kupdate and such).
 *   We wait on commit, if told to.
 *
 * - Within iput_final() -> write_inode_now()
 *   We wait on commit, if told to.
 *
 * In all cases it is actually safe for us to return without doing anything,
 * because the inode has been copied into a raw inode buffer in
 * ext4_mark_inode_dirty().  This is a correctness thing for WB_SYNC_ALL
 * writeback.
 *
 * Note that we are absolutely dependent upon all inode dirtiers doing the
 * right thing: they *must* call mark_inode_dirty() after dirtying info in
 * which we are interested.
 *
 * It would be a bug for them to not do this.  The code:
 *
 *      mark_inode_dirty(inode)
 *      stuff();
 *      inode->i_size = expr;
 *
 * is in error because write_inode() could occur while `stuff()' is running,
 * and the new i_size will be lost.  Plus the inode will no longer be on the
 * superblock's dirty inode list.
 */
int ext4_write_inode(struct inode *inode, struct writeback_control *wbc)
{
        int err;

        if (WARN_ON_ONCE(current->flags & PF_MEMALLOC))
                return 0;

        if (EXT4_SB(inode->i_sb)->s_journal) {
                if (ext4_journal_current_handle()) {
                        jbd_debug(1, "called recursively, non-PF_MEMALLOC!\n");
                        dump_stack();
                        return -EIO;
                }

                /*
                 * No need to force transaction in WB_SYNC_NONE mode. Also
                 * ext4_sync_fs() will force the commit after everything is
                 * written.
                 */
                if (wbc->sync_mode != WB_SYNC_ALL || wbc->for_sync)
                        return 0;

                err = ext4_force_commit(inode->i_sb);
        } else {
                struct ext4_iloc iloc;

                err = __ext4_get_inode_loc(inode, &iloc, 0);
                if (err)
                        return err;
                /*
                 * sync(2) will flush the whole buffer cache. No need to do
                 * it here separately for each inode.
                 */
                if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync)
                        sync_dirty_buffer(iloc.bh);
                if (buffer_req(iloc.bh) && !buffer_uptodate(iloc.bh)) {
                        EXT4_ERROR_INODE_BLOCK(inode, iloc.bh->b_blocknr,
                                         "IO error syncing inode");
                        err = -EIO;
                }
                brelse(iloc.bh);
        }
        return err;
}

/*
 * In data=journal mode ext4_journalled_invalidatepage() may fail to invalidate
 * buffers that are attached to a page stradding i_size and are undergoing
 * commit. In that case we have to wait for commit to finish and try again.
 */
static void ext4_wait_for_tail_page_commit(struct inode *inode)
{
        struct page *page;
        unsigned offset;
        journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
        tid_t commit_tid = 0;
        int ret;

        offset = inode->i_size & (PAGE_CACHE_SIZE - 1);
        /*
         * All buffers in the last page remain valid? Then there's nothing to
         * do. We do the check mainly to optimize the common PAGE_CACHE_SIZE ==
         * blocksize case
         */
        if (offset > PAGE_CACHE_SIZE - (1 << inode->i_blkbits))
                return;
        while (1) {
                page = find_lock_page(inode->i_mapping,
                                      inode->i_size >> PAGE_CACHE_SHIFT);
                if (!page)
                        return;
                ret = __ext4_journalled_invalidatepage(page, offset,
                                                PAGE_CACHE_SIZE - offset);
                unlock_page(page);
                page_cache_release(page);
                if (ret != -EBUSY)
                        return;
                commit_tid = 0;
                read_lock(&journal->j_state_lock);
                if (journal->j_committing_transaction)
                        commit_tid = journal->j_committing_transaction->t_tid;
                read_unlock(&journal->j_state_lock);
                if (commit_tid)
                        jbd2_log_wait_commit(journal, commit_tid);
        }
}

/*
 * ext4_setattr()
 *
 * Called from notify_change.
 *
 * We want to trap VFS attempts to truncate the file as soon as
 * possible.  In particular, we want to make sure that when the VFS
 * shrinks i_size, we put the inode on the orphan list and modify
 * i_disksize immediately, so that during the subsequent flushing of
 * dirty pages and freeing of disk blocks, we can guarantee that any
 * commit will leave the blocks being flushed in an unused state on
 * disk.  (On recovery, the inode will get truncated and the blocks will
 * be freed, so we have a strong guarantee that no future commit will
 * leave these blocks visible to the user.)
 *
 * Another thing we have to assure is that if we are in ordered mode
 * and inode is still attached to the committing transaction, we must
 * we start writeout of all the dirty pages which are being truncated.
 * This way we are sure that all the data written in the previous
 * transaction are already on disk (truncate waits for pages under
 * writeback).
 *
 * Called with inode->i_mutex down.
 */
int ext4_setattr(struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = dentry->d_inode;
        int error, rc = 0;
        int orphan = 0;
        const unsigned int ia_valid = attr->ia_valid;

        error = inode_change_ok(inode, attr);
        if (error)
                return error;

        if (is_quota_modification(inode, attr))
                dquot_initialize(inode);
        if ((ia_valid & ATTR_UID && !uid_eq(attr->ia_uid, inode->i_uid)) ||
            (ia_valid & ATTR_GID && !gid_eq(attr->ia_gid, inode->i_gid))) {
                handle_t *handle;

                /* (user+group)*(old+new) structure, inode write (sb,
                 * inode block, ? - but truncate inode update has it) */
                handle = ext4_journal_start(inode, EXT4_HT_QUOTA,
                        (EXT4_MAXQUOTAS_INIT_BLOCKS(inode->i_sb) +
                         EXT4_MAXQUOTAS_DEL_BLOCKS(inode->i_sb)) + 3);
                if (IS_ERR(handle)) {
                        error = PTR_ERR(handle);
                        goto err_out;
                }
                error = dquot_transfer(inode, attr);
                if (error) {
                        ext4_journal_stop(handle);
                        return error;
                }
                /* Update corresponding info in inode so that everything is in
                 * one transaction */
                if (attr->ia_valid & ATTR_UID)
                        inode->i_uid = attr->ia_uid;
                if (attr->ia_valid & ATTR_GID)
                        inode->i_gid = attr->ia_gid;
                error = ext4_mark_inode_dirty(handle, inode);
                ext4_journal_stop(handle);
        }

        if (attr->ia_valid & ATTR_SIZE && attr->ia_size != inode->i_size) {
                handle_t *handle;

                if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
                        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);

                        if (attr->ia_size > sbi->s_bitmap_maxbytes)
                                return -EFBIG;
                }

                if (IS_I_VERSION(inode) && attr->ia_size != inode->i_size)
                        inode_inc_iversion(inode);

                if (S_ISREG(inode->i_mode) &&
                    (attr->ia_size < inode->i_size)) {
                        if (ext4_should_order_data(inode)) {
                                error = ext4_begin_ordered_truncate(inode,
                                                            attr->ia_size);
                                if (error)
                                        goto err_out;
                        }
                        handle = ext4_journal_start(inode, EXT4_HT_INODE, 3);
                        if (IS_ERR(handle)) {
                                error = PTR_ERR(handle);
                                goto err_out;
                        }
                        if (ext4_handle_valid(handle)) {
                                error = ext4_orphan_add(handle, inode);
                                orphan = 1;
                        }
                        down_write(&EXT4_I(inode)->i_data_sem);
                        EXT4_I(inode)->i_disksize = attr->ia_size;
                        rc = ext4_mark_inode_dirty(handle, inode);
                        if (!error)
                                error = rc;
                        /*
                         * We have to update i_size under i_data_sem together
                         * with i_disksize to avoid races with writeback code
                         * running ext4_wb_update_i_disksize().
                         */
                        if (!error)
                                i_size_write(inode, attr->ia_size);
                        up_write(&EXT4_I(inode)->i_data_sem);
                        ext4_journal_stop(handle);
                        if (error) {
                                ext4_orphan_del(NULL, inode);
                                goto err_out;
                        }
                } else {
                        loff_t oldsize = inode->i_size;

                        i_size_write(inode, attr->ia_size);
                        pagecache_isize_extended(inode, oldsize, inode->i_size);
                }

                /*
                 * Blocks are going to be removed from the inode. Wait
                 * for dio in flight.  Temporarily disable
                 * dioread_nolock to prevent livelock.
                 */
                if (orphan) {
                        if (!ext4_should_journal_data(inode)) {
                                ext4_inode_block_unlocked_dio(inode);
                                inode_dio_wait(inode);
                                ext4_inode_resume_unlocked_dio(inode);
                        } else
                                ext4_wait_for_tail_page_commit(inode);
                }
                /*
                 * Truncate pagecache after we've waited for commit
                 * in data=journal mode to make pages freeable.
                 */
                        truncate_pagecache(inode, inode->i_size);
        }
        /*
         * We want to call ext4_truncate() even if attr->ia_size ==
         * inode->i_size for cases like truncation of fallocated space
         */
        if (attr->ia_valid & ATTR_SIZE)
                ext4_truncate(inode);

        if (!rc) {
                setattr_copy(inode, attr);
                mark_inode_dirty(inode);
        }

        /*
         * If the call to ext4_truncate failed to get a transaction handle at
         * all, we need to clean up the in-core orphan list manually.
         */
        if (orphan && inode->i_nlink)
                ext4_orphan_del(NULL, inode);

        if (!rc && (ia_valid & ATTR_MODE))
                rc = posix_acl_chmod(inode, inode->i_mode);

err_out:
        ext4_std_error(inode->i_sb, error);
        if (!error)
                error = rc;
        return error;
}

int ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
                 struct kstat *stat)
{
        struct inode *inode;
        unsigned long long delalloc_blocks;

        inode = dentry->d_inode;
        generic_fillattr(inode, stat);

        /*
         * If there is inline data in the inode, the inode will normally not
         * have data blocks allocated (it may have an external xattr block).
         * Report at least one sector for such files, so tools like tar, rsync,
         * others doen't incorrectly think the file is completely sparse.
         */
        if (unlikely(ext4_has_inline_data(inode)))
                stat->blocks += (stat->size + 511) >> 9;

        /*
         * We can't update i_blocks if the block allocation is delayed
         * otherwise in the case of system crash before the real block
         * allocation is done, we will have i_blocks inconsistent with
         * on-disk file blocks.
         * We always keep i_blocks updated together with real
         * allocation. But to not confuse with user, stat
         * will return the blocks that include the delayed allocation
         * blocks for this file.
         */
        delalloc_blocks = EXT4_C2B(EXT4_SB(inode->i_sb),
                                   EXT4_I(inode)->i_reserved_data_blocks);
        stat->blocks += delalloc_blocks << (inode->i_sb->s_blocksize_bits - 9);
        return 0;
}

static int ext4_index_trans_blocks(struct inode *inode, int lblocks,
                                   int pextents)
{
        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
                return ext4_ind_trans_blocks(inode, lblocks);
        return ext4_ext_index_trans_blocks(inode, pextents);
}

/*
 * Account for index blocks, block groups bitmaps and block group
 * descriptor blocks if modify datablocks and index blocks
 * worse case, the indexs blocks spread over different block groups
 *
 * If datablocks are discontiguous, they are possible to spread over
 * different block groups too. If they are contiguous, with flexbg,
 * they could still across block group boundary.
 *
 * Also account for superblock, inode, quota and xattr blocks
 */
static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
                                  int pextents)
{
        ext4_group_t groups, ngroups = ext4_get_groups_count(inode->i_sb);
        int gdpblocks;
        int idxblocks;
        int ret = 0;

        /*
         * How many index blocks need to touch to map @lblocks logical blocks
         * to @pextents physical extents?
         */
        idxblocks = ext4_index_trans_blocks(inode, lblocks, pextents);

        ret = idxblocks;

        /*
         * Now let's see how many group bitmaps and group descriptors need
         * to account
         */
        groups = idxblocks + pextents;
        gdpblocks = groups;
        if (groups > ngroups)
                groups = ngroups;
        if (groups > EXT4_SB(inode->i_sb)->s_gdb_count)
                gdpblocks = EXT4_SB(inode->i_sb)->s_gdb_count;

        /* bitmaps and block group descriptor blocks */
        ret += groups + gdpblocks;

        /* Blocks for super block, inode, quota and xattr blocks */
        ret += EXT4_META_TRANS_BLOCKS(inode->i_sb);

        return ret;
}

/*
 * Calculate the total number of credits to reserve to fit
 * the modification of a single pages into a single transaction,
 * which may include multiple chunks of block allocations.
 *
 * This could be called via ext4_write_begin()
 *
 * We need to consider the worse case, when
 * one new block per extent.
 */
int ext4_writepage_trans_blocks(struct inode *inode)
{
        int bpp = ext4_journal_blocks_per_page(inode);
        int ret;

        ret = ext4_meta_trans_blocks(inode, bpp, bpp);

        /* Account for data blocks for journalled mode */
        if (ext4_should_journal_data(inode))
                ret += bpp;
        return ret;
}

/*
 * Calculate the journal credits for a chunk of data modification.
 *
 * This is called from DIO, fallocate or whoever calling
 * ext4_map_blocks() to map/allocate a chunk of contiguous disk blocks.
 *
 * journal buffers for data blocks are not included here, as DIO
 * and fallocate do no need to journal data buffers.
 */
int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
{
        return ext4_meta_trans_blocks(inode, nrblocks, 1);
}

/*
 * The caller must have previously called ext4_reserve_inode_write().
 * Give this, we know that the caller already has write access to iloc->bh.
 */
int ext4_mark_iloc_dirty(handle_t *handle,
                         struct inode *inode, struct ext4_iloc *iloc)
{
        int err = 0;

        if (IS_I_VERSION(inode))
                inode_inc_iversion(inode);

        /* the do_update_inode consumes one bh->b_count */
        get_bh(iloc->bh);

        /* ext4_do_update_inode() does jbd2_journal_dirty_metadata */
        err = ext4_do_update_inode(handle, inode, iloc);
        put_bh(iloc->bh);
        return err;
}

/*
 * On success, We end up with an outstanding reference count against
 * iloc->bh.  This _must_ be cleaned up later.
 */

int
ext4_reserve_inode_write(handle_t *handle, struct inode *inode,
                         struct ext4_iloc *iloc)
{
        int err;

        err = ext4_get_inode_loc(inode, iloc);
        if (!err) {
                BUFFER_TRACE(iloc->bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, iloc->bh);
                if (err) {
                        brelse(iloc->bh);
                        iloc->bh = NULL;
                }
        }
        ext4_std_error(inode->i_sb, err);
        return err;
}

/*
 * Expand an inode by new_extra_isize bytes.
 * Returns 0 on success or negative error number on failure.
 */
static int ext4_expand_extra_isize(struct inode *inode,
                                   unsigned int new_extra_isize,
                                   struct ext4_iloc iloc,
                                   handle_t *handle)
{
        struct ext4_inode *raw_inode;
        struct ext4_xattr_ibody_header *header;

        if (EXT4_I(inode)->i_extra_isize >= new_extra_isize)
                return 0;

        raw_inode = ext4_raw_inode(&iloc);

        header = IHDR(inode, raw_inode);

        /* No extended attributes present */
        if (!ext4_test_inode_state(inode, EXT4_STATE_XATTR) ||
            header->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC)) {
                memset((void *)raw_inode + EXT4_GOOD_OLD_INODE_SIZE, 0,
                        new_extra_isize);
                EXT4_I(inode)->i_extra_isize = new_extra_isize;
                return 0;
        }

        /* try to expand with EAs present */
        return ext4_expand_extra_isize_ea(inode, new_extra_isize,
                                          raw_inode, handle);
}

/*
 * What we do here is to mark the in-core inode as clean with respect to inode
 * dirtiness (it may still be data-dirty).
 * This means that the in-core inode may be reaped by prune_icache
 * without having to perform any I/O.  This is a very good thing,
 * because *any* task may call prune_icache - even ones which
 * have a transaction open against a different journal.
 *
 * Is this cheating?  Not really.  Sure, we haven't written the
 * inode out, but prune_icache isn't a user-visible syncing function.
 * Whenever the user wants stuff synced (sys_sync, sys_msync, sys_fsync)
 * we start and wait on commits.
 */
int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
{
        struct ext4_iloc iloc;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        static unsigned int mnt_count;
        int err, ret;

        might_sleep();
        trace_ext4_mark_inode_dirty(inode, _RET_IP_);
        err = ext4_reserve_inode_write(handle, inode, &iloc);
        if (err)
                return err;
        if (ext4_handle_valid(handle) &&
            EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
            !ext4_test_inode_state(inode, EXT4_STATE_NO_EXPAND)) {
                /*
                 * We need extra buffer credits since we may write into EA block
                 * with this same handle. If journal_extend fails, then it will
                 * only result in a minor loss of functionality for that inode.
                 * If this is felt to be critical, then e2fsck should be run to
                 * force a large enough s_min_extra_isize.
                 */
                if ((jbd2_journal_extend(handle,
                             EXT4_DATA_TRANS_BLOCKS(inode->i_sb))) == 0) {
                        ret = ext4_expand_extra_isize(inode,
                                                      sbi->s_want_extra_isize,
                                                      iloc, handle);
                        if (ret) {
                                ext4_set_inode_state(inode,
                                                     EXT4_STATE_NO_EXPAND);
                                if (mnt_count !=
                                        le16_to_cpu(sbi->s_es->s_mnt_count)) {
                                        ext4_warning(inode->i_sb,
                                        "Unable to expand inode %lu. Delete"
                                        " some EAs or run e2fsck.",
                                        inode->i_ino);
                                        mnt_count =
                                          le16_to_cpu(sbi->s_es->s_mnt_count);
                                }
                        }
                }
        }
        return ext4_mark_iloc_dirty(handle, inode, &iloc);
}

/*
 * ext4_dirty_inode() is called from __mark_inode_dirty()
 *
 * We're really interested in the case where a file is being extended.
 * i_size has been changed by generic_commit_write() and we thus need
 * to include the updated inode in the current transaction.
 *
 * Also, dquot_alloc_block() will always dirty the inode when blocks
 * are allocated to the file.
 *
 * If the inode is marked synchronous, we don't honour that here - doing
 * so would cause a commit on atime updates, which we don't bother doing.
 * We handle synchronous inodes at the highest possible level.
 */
void ext4_dirty_inode(struct inode *inode, int flags)
{
        handle_t *handle;

        handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
        if (IS_ERR(handle))
                goto out;

        ext4_mark_inode_dirty(handle, inode);

        ext4_journal_stop(handle);
out:
        return;
}

#if 0
/*
 * Bind an inode's backing buffer_head into this transaction, to prevent
 * it from being flushed to disk early.  Unlike
 * ext4_reserve_inode_write, this leaves behind no bh reference and
 * returns no iloc structure, so the caller needs to repeat the iloc
 * lookup to mark the inode dirty later.
 */
static int ext4_pin_inode(handle_t *handle, struct inode *inode)
{
        struct ext4_iloc iloc;

        int err = 0;
        if (handle) {
                err = ext4_get_inode_loc(inode, &iloc);
                if (!err) {
                        BUFFER_TRACE(iloc.bh, "get_write_access");
                        err = jbd2_journal_get_write_access(handle, iloc.bh);
                        if (!err)
                                err = ext4_handle_dirty_metadata(handle,
                                                                 NULL,
                                                                 iloc.bh);
                        brelse(iloc.bh);
                }
        }
        ext4_std_error(inode->i_sb, err);
        return err;
}
#endif

int ext4_change_inode_journal_flag(struct inode *inode, int val)
{
        journal_t *journal;
        handle_t *handle;
        int err;

        /*
         * We have to be very careful here: changing a data block's
         * journaling status dynamically is dangerous.  If we write a
         * data block to the journal, change the status and then delete
         * that block, we risk forgetting to revoke the old log record
         * from the journal and so a subsequent replay can corrupt data.
         * So, first we make sure that the journal is empty and that
         * nobody is changing anything.
         */

        journal = EXT4_JOURNAL(inode);
        if (!journal)
                return 0;
        if (is_journal_aborted(journal))
                return -EROFS;
        /* We have to allocate physical blocks for delalloc blocks
         * before flushing journal. otherwise delalloc blocks can not
         * be allocated any more. even more truncate on delalloc blocks
         * could trigger BUG by flushing delalloc blocks in journal.
         * There is no delalloc block in non-journal data mode.
         */
        if (val && test_opt(inode->i_sb, DELALLOC)) {
                err = ext4_alloc_da_blocks(inode);
                if (err < 0)
                        return err;
        }

        /* Wait for all existing dio workers */
        ext4_inode_block_unlocked_dio(inode);
        inode_dio_wait(inode);

        jbd2_journal_lock_updates(journal);

        /*
         * OK, there are no updates running now, and all cached data is
         * synced to disk.  We are now in a completely consistent state
         * which doesn't have anything in the journal, and we know that
         * no filesystem updates are running, so it is safe to modify
         * the inode's in-core data-journaling state flag now.
         */

        if (val)
                ext4_set_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
        else {
                jbd2_journal_flush(journal);
                ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
        }
        ext4_set_aops(inode);

        jbd2_journal_unlock_updates(journal);
        ext4_inode_resume_unlocked_dio(inode);

        /* Finally we can mark the inode as dirty. */

        handle = ext4_journal_start(inode, EXT4_HT_INODE, 1);
        if (IS_ERR(handle))
                return PTR_ERR(handle);

        err = ext4_mark_inode_dirty(handle, inode);
        ext4_handle_sync(handle);
        ext4_journal_stop(handle);
        ext4_std_error(inode->i_sb, err);

        return err;
}

static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
{
        return !buffer_mapped(bh);
}

int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct page *page = vmf->page;
        loff_t size;
        unsigned long len;
        int ret;
        struct file *file = vma->vm_file;
        struct inode *inode = file_inode(file);
        struct address_space *mapping = inode->i_mapping;
        handle_t *handle;
        get_block_t *get_block;
        int retries = 0;

        sb_start_pagefault(inode->i_sb);
        file_update_time(vma->vm_file);
        /* Delalloc case is easy... */
        if (test_opt(inode->i_sb, DELALLOC) &&
            !ext4_should_journal_data(inode) &&
            !ext4_nonda_switch(inode->i_sb)) {
                do {
                        ret = __block_page_mkwrite(vma, vmf,
                                                   ext4_da_get_block_prep);
                } while (ret == -ENOSPC &&
                       ext4_should_retry_alloc(inode->i_sb, &retries));
                goto out_ret;
        }

        lock_page(page);
        size = i_size_read(inode);
        /* Page got truncated from under us? */
        if (page->mapping != mapping || page_offset(page) > size) {
                unlock_page(page);
                ret = VM_FAULT_NOPAGE;
                goto out;
        }

        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;
        /*
         * Return if we have all the buffers mapped. This avoids the need to do
         * journal_start/journal_stop which can block and take a long time
         */
        if (page_has_buffers(page)) {
                if (!ext4_walk_page_buffers(NULL, page_buffers(page),
                                            0, len, NULL,
                                            ext4_bh_unmapped)) {
                        /* Wait so that we don't change page under IO */
                        wait_for_stable_page(page);
                        ret = VM_FAULT_LOCKED;
                        goto out;
                }
        }
        unlock_page(page);
        /* OK, we need to fill the hole... */
        if (ext4_should_dioread_nolock(inode))
                get_block = ext4_get_block_write;
        else
                get_block = ext4_get_block;
retry_alloc:
        handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
                                    ext4_writepage_trans_blocks(inode));
        if (IS_ERR(handle)) {
                ret = VM_FAULT_SIGBUS;
                goto out;
        }
        ret = __block_page_mkwrite(vma, vmf, get_block);
        if (!ret && ext4_should_journal_data(inode)) {
                if (ext4_walk_page_buffers(handle, page_buffers(page), 0,
                          PAGE_CACHE_SIZE, NULL, do_journal_get_write_access)) {
                        unlock_page(page);
                        ret = VM_FAULT_SIGBUS;
                        ext4_journal_stop(handle);
                        goto out;
                }
                ext4_set_inode_state(inode, EXT4_STATE_JDATA);
        }
        ext4_journal_stop(handle);
        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry_alloc;
out_ret:
        ret = block_page_mkwrite_return(ret);
out:
        sb_end_pagefault(inode->i_sb);
        return ret;
}