MIPS: Octeon: Remove checks for CONFIG_CAVIUM_GDB

[linux/fpc-iii.git] / fs / xfs / xfs_aops.c

/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_inode_item.h"
#include "xfs_alloc.h"
#include "xfs_error.h"
#include "xfs_iomap.h"
#include "xfs_trace.h"
#include "xfs_bmap.h"
#include "xfs_bmap_util.h"
#include "xfs_bmap_btree.h"
#include "xfs_dinode.h"
#include <linux/aio.h>
#include <linux/gfp.h>
#include <linux/mpage.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>

void
xfs_count_page_state(
        struct page             *page,
        int                     *delalloc,
        int                     *unwritten)
{
        struct buffer_head      *bh, *head;

        *delalloc = *unwritten = 0;

        bh = head = page_buffers(page);
        do {
                if (buffer_unwritten(bh))
                        (*unwritten) = 1;
                else if (buffer_delay(bh))
                        (*delalloc) = 1;
        } while ((bh = bh->b_this_page) != head);
}

STATIC struct block_device *
xfs_find_bdev_for_inode(
        struct inode            *inode)
{
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;

        if (XFS_IS_REALTIME_INODE(ip))
                return mp->m_rtdev_targp->bt_bdev;
        else
                return mp->m_ddev_targp->bt_bdev;
}

/*
 * We're now finished for good with this ioend structure.
 * Update the page state via the associated buffer_heads,
 * release holds on the inode and bio, and finally free
 * up memory.  Do not use the ioend after this.
 */
STATIC void
xfs_destroy_ioend(
        xfs_ioend_t             *ioend)
{
        struct buffer_head      *bh, *next;

        for (bh = ioend->io_buffer_head; bh; bh = next) {
                next = bh->b_private;
                bh->b_end_io(bh, !ioend->io_error);
        }

        mempool_free(ioend, xfs_ioend_pool);
}

/*
 * Fast and loose check if this write could update the on-disk inode size.
 */
static inline bool xfs_ioend_is_append(struct xfs_ioend *ioend)
{
        return ioend->io_offset + ioend->io_size >
                XFS_I(ioend->io_inode)->i_d.di_size;
}

STATIC int
xfs_setfilesize_trans_alloc(
        struct xfs_ioend        *ioend)
{
        struct xfs_mount        *mp = XFS_I(ioend->io_inode)->i_mount;
        struct xfs_trans        *tp;
        int                     error;

        tp = xfs_trans_alloc(mp, XFS_TRANS_FSYNC_TS);

        error = xfs_trans_reserve(tp, &M_RES(mp)->tr_fsyncts, 0, 0);
        if (error) {
                xfs_trans_cancel(tp, 0);
                return error;
        }

        ioend->io_append_trans = tp;

        /*
         * We may pass freeze protection with a transaction.  So tell lockdep
         * we released it.
         */
        rwsem_release(&ioend->io_inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
                      1, _THIS_IP_);
        /*
         * We hand off the transaction to the completion thread now, so
         * clear the flag here.
         */
        current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
        return 0;
}

/*
 * Update on-disk file size now that data has been written to disk.
 */
STATIC int
xfs_setfilesize(
        struct xfs_ioend        *ioend)
{
        struct xfs_inode        *ip = XFS_I(ioend->io_inode);
        struct xfs_trans        *tp = ioend->io_append_trans;
        xfs_fsize_t             isize;

        /*
         * The transaction may have been allocated in the I/O submission thread,
         * thus we need to mark ourselves as beeing in a transaction manually.
         * Similarly for freeze protection.
         */
        current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
        rwsem_acquire_read(&VFS_I(ip)->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
                           0, 1, _THIS_IP_);

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        isize = xfs_new_eof(ip, ioend->io_offset + ioend->io_size);
        if (!isize) {
                xfs_iunlock(ip, XFS_ILOCK_EXCL);
                xfs_trans_cancel(tp, 0);
                return 0;
        }

        trace_xfs_setfilesize(ip, ioend->io_offset, ioend->io_size);

        ip->i_d.di_size = isize;
        xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
        xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);

        return xfs_trans_commit(tp, 0);
}

/*
 * Schedule IO completion handling on the final put of an ioend.
 *
 * If there is no work to do we might as well call it a day and free the
 * ioend right now.
 */
STATIC void
xfs_finish_ioend(
        struct xfs_ioend        *ioend)
{
        if (atomic_dec_and_test(&ioend->io_remaining)) {
                struct xfs_mount        *mp = XFS_I(ioend->io_inode)->i_mount;

                if (ioend->io_type == XFS_IO_UNWRITTEN)
                        queue_work(mp->m_unwritten_workqueue, &ioend->io_work);
                else if (ioend->io_append_trans ||
                         (ioend->io_isdirect && xfs_ioend_is_append(ioend)))
                        queue_work(mp->m_data_workqueue, &ioend->io_work);
                else
                        xfs_destroy_ioend(ioend);
        }
}

/*
 * IO write completion.
 */
STATIC void
xfs_end_io(
        struct work_struct *work)
{
        xfs_ioend_t     *ioend = container_of(work, xfs_ioend_t, io_work);
        struct xfs_inode *ip = XFS_I(ioend->io_inode);
        int             error = 0;

        if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                ioend->io_error = -EIO;
                goto done;
        }
        if (ioend->io_error)
                goto done;

        /*
         * For unwritten extents we need to issue transactions to convert a
         * range to normal written extens after the data I/O has finished.
         */
        if (ioend->io_type == XFS_IO_UNWRITTEN) {
                error = xfs_iomap_write_unwritten(ip, ioend->io_offset,
                                                  ioend->io_size);
        } else if (ioend->io_isdirect && xfs_ioend_is_append(ioend)) {
                /*
                 * For direct I/O we do not know if we need to allocate blocks
                 * or not so we can't preallocate an append transaction as that
                 * results in nested reservations and log space deadlocks. Hence
                 * allocate the transaction here. While this is sub-optimal and
                 * can block IO completion for some time, we're stuck with doing
                 * it this way until we can pass the ioend to the direct IO
                 * allocation callbacks and avoid nesting that way.
                 */
                error = xfs_setfilesize_trans_alloc(ioend);
                if (error)
                        goto done;
                error = xfs_setfilesize(ioend);
        } else if (ioend->io_append_trans) {
                error = xfs_setfilesize(ioend);
        } else {
                ASSERT(!xfs_ioend_is_append(ioend));
        }

done:
        if (error)
                ioend->io_error = -error;
        xfs_destroy_ioend(ioend);
}

/*
 * Call IO completion handling in caller context on the final put of an ioend.
 */
STATIC void
xfs_finish_ioend_sync(
        struct xfs_ioend        *ioend)
{
        if (atomic_dec_and_test(&ioend->io_remaining))
                xfs_end_io(&ioend->io_work);
}

/*
 * Allocate and initialise an IO completion structure.
 * We need to track unwritten extent write completion here initially.
 * We'll need to extend this for updating the ondisk inode size later
 * (vs. incore size).
 */
STATIC xfs_ioend_t *
xfs_alloc_ioend(
        struct inode            *inode,
        unsigned int            type)
{
        xfs_ioend_t             *ioend;

        ioend = mempool_alloc(xfs_ioend_pool, GFP_NOFS);

        /*
         * Set the count to 1 initially, which will prevent an I/O
         * completion callback from happening before we have started
         * all the I/O from calling the completion routine too early.
         */
        atomic_set(&ioend->io_remaining, 1);
        ioend->io_isdirect = 0;
        ioend->io_error = 0;
        ioend->io_list = NULL;
        ioend->io_type = type;
        ioend->io_inode = inode;
        ioend->io_buffer_head = NULL;
        ioend->io_buffer_tail = NULL;
        ioend->io_offset = 0;
        ioend->io_size = 0;
        ioend->io_append_trans = NULL;

        INIT_WORK(&ioend->io_work, xfs_end_io);
        return ioend;
}

STATIC int
xfs_map_blocks(
        struct inode            *inode,
        loff_t                  offset,
        struct xfs_bmbt_irec    *imap,
        int                     type,
        int                     nonblocking)
{
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
        ssize_t                 count = 1 << inode->i_blkbits;
        xfs_fileoff_t           offset_fsb, end_fsb;
        int                     error = 0;
        int                     bmapi_flags = XFS_BMAPI_ENTIRE;
        int                     nimaps = 1;

        if (XFS_FORCED_SHUTDOWN(mp))
                return -XFS_ERROR(EIO);

        if (type == XFS_IO_UNWRITTEN)
                bmapi_flags |= XFS_BMAPI_IGSTATE;

        if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED)) {
                if (nonblocking)
                        return -XFS_ERROR(EAGAIN);
                xfs_ilock(ip, XFS_ILOCK_SHARED);
        }

        ASSERT(ip->i_d.di_format != XFS_DINODE_FMT_BTREE ||
               (ip->i_df.if_flags & XFS_IFEXTENTS));
        ASSERT(offset <= mp->m_super->s_maxbytes);

        if (offset + count > mp->m_super->s_maxbytes)
                count = mp->m_super->s_maxbytes - offset;
        end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
        offset_fsb = XFS_B_TO_FSBT(mp, offset);
        error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
                                imap, &nimaps, bmapi_flags);
        xfs_iunlock(ip, XFS_ILOCK_SHARED);

        if (error)
                return -XFS_ERROR(error);

        if (type == XFS_IO_DELALLOC &&
            (!nimaps || isnullstartblock(imap->br_startblock))) {
                error = xfs_iomap_write_allocate(ip, offset, imap);
                if (!error)
                        trace_xfs_map_blocks_alloc(ip, offset, count, type, imap);
                return -XFS_ERROR(error);
        }

#ifdef DEBUG
        if (type == XFS_IO_UNWRITTEN) {
                ASSERT(nimaps);
                ASSERT(imap->br_startblock != HOLESTARTBLOCK);
                ASSERT(imap->br_startblock != DELAYSTARTBLOCK);
        }
#endif
        if (nimaps)
                trace_xfs_map_blocks_found(ip, offset, count, type, imap);
        return 0;
}

STATIC int
xfs_imap_valid(
        struct inode            *inode,
        struct xfs_bmbt_irec    *imap,
        xfs_off_t               offset)
{
        offset >>= inode->i_blkbits;

        return offset >= imap->br_startoff &&
                offset < imap->br_startoff + imap->br_blockcount;
}

/*
 * BIO completion handler for buffered IO.
 */
STATIC void
xfs_end_bio(
        struct bio              *bio,
        int                     error)
{
        xfs_ioend_t             *ioend = bio->bi_private;

        ASSERT(atomic_read(&bio->bi_cnt) >= 1);
        ioend->io_error = test_bit(BIO_UPTODATE, &bio->bi_flags) ? 0 : error;

        /* Toss bio and pass work off to an xfsdatad thread */
        bio->bi_private = NULL;
        bio->bi_end_io = NULL;
        bio_put(bio);

        xfs_finish_ioend(ioend);
}

STATIC void
xfs_submit_ioend_bio(
        struct writeback_control *wbc,
        xfs_ioend_t             *ioend,
        struct bio              *bio)
{
        atomic_inc(&ioend->io_remaining);
        bio->bi_private = ioend;
        bio->bi_end_io = xfs_end_bio;
        submit_bio(wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE, bio);
}

STATIC struct bio *
xfs_alloc_ioend_bio(
        struct buffer_head      *bh)
{
        int                     nvecs = bio_get_nr_vecs(bh->b_bdev);
        struct bio              *bio = bio_alloc(GFP_NOIO, nvecs);

        ASSERT(bio->bi_private == NULL);
        bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
        bio->bi_bdev = bh->b_bdev;
        return bio;
}

STATIC void
xfs_start_buffer_writeback(
        struct buffer_head      *bh)
{
        ASSERT(buffer_mapped(bh));
        ASSERT(buffer_locked(bh));
        ASSERT(!buffer_delay(bh));
        ASSERT(!buffer_unwritten(bh));

        mark_buffer_async_write(bh);
        set_buffer_uptodate(bh);
        clear_buffer_dirty(bh);
}

STATIC void
xfs_start_page_writeback(
        struct page             *page,
        int                     clear_dirty,
        int                     buffers)
{
        ASSERT(PageLocked(page));
        ASSERT(!PageWriteback(page));
        if (clear_dirty)
                clear_page_dirty_for_io(page);
        set_page_writeback(page);
        unlock_page(page);
        /* If no buffers on the page are to be written, finish it here */
        if (!buffers)
                end_page_writeback(page);
}

static inline int xfs_bio_add_buffer(struct bio *bio, struct buffer_head *bh)
{
        return bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
}

/*
 * Submit all of the bios for all of the ioends we have saved up, covering the
 * initial writepage page and also any probed pages.
 *
 * Because we may have multiple ioends spanning a page, we need to start
 * writeback on all the buffers before we submit them for I/O. If we mark the
 * buffers as we got, then we can end up with a page that only has buffers
 * marked async write and I/O complete on can occur before we mark the other
 * buffers async write.
 *
 * The end result of this is that we trip a bug in end_page_writeback() because
 * we call it twice for the one page as the code in end_buffer_async_write()
 * assumes that all buffers on the page are started at the same time.
 *
 * The fix is two passes across the ioend list - one to start writeback on the
 * buffer_heads, and then submit them for I/O on the second pass.
 *
 * If @fail is non-zero, it means that we have a situation where some part of
 * the submission process has failed after we have marked paged for writeback
 * and unlocked them. In this situation, we need to fail the ioend chain rather
 * than submit it to IO. This typically only happens on a filesystem shutdown.
 */
STATIC void
xfs_submit_ioend(
        struct writeback_control *wbc,
        xfs_ioend_t             *ioend,
        int                     fail)
{
        xfs_ioend_t             *head = ioend;
        xfs_ioend_t             *next;
        struct buffer_head      *bh;
        struct bio              *bio;
        sector_t                lastblock = 0;

        /* Pass 1 - start writeback */
        do {
                next = ioend->io_list;
                for (bh = ioend->io_buffer_head; bh; bh = bh->b_private)
                        xfs_start_buffer_writeback(bh);
        } while ((ioend = next) != NULL);

        /* Pass 2 - submit I/O */
        ioend = head;
        do {
                next = ioend->io_list;
                bio = NULL;

                /*
                 * If we are failing the IO now, just mark the ioend with an
                 * error and finish it. This will run IO completion immediately
                 * as there is only one reference to the ioend at this point in
                 * time.
                 */
                if (fail) {
                        ioend->io_error = -fail;
                        xfs_finish_ioend(ioend);
                        continue;
                }

                for (bh = ioend->io_buffer_head; bh; bh = bh->b_private) {

                        if (!bio) {
 retry:
                                bio = xfs_alloc_ioend_bio(bh);
                        } else if (bh->b_blocknr != lastblock + 1) {
                                xfs_submit_ioend_bio(wbc, ioend, bio);
                                goto retry;
                        }

                        if (xfs_bio_add_buffer(bio, bh) != bh->b_size) {
                                xfs_submit_ioend_bio(wbc, ioend, bio);
                                goto retry;
                        }

                        lastblock = bh->b_blocknr;
                }
                if (bio)
                        xfs_submit_ioend_bio(wbc, ioend, bio);
                xfs_finish_ioend(ioend);
        } while ((ioend = next) != NULL);
}

/*
 * Cancel submission of all buffer_heads so far in this endio.
 * Toss the endio too.  Only ever called for the initial page
 * in a writepage request, so only ever one page.
 */
STATIC void
xfs_cancel_ioend(
        xfs_ioend_t             *ioend)
{
        xfs_ioend_t             *next;
        struct buffer_head      *bh, *next_bh;

        do {
                next = ioend->io_list;
                bh = ioend->io_buffer_head;
                do {
                        next_bh = bh->b_private;
                        clear_buffer_async_write(bh);
                        unlock_buffer(bh);
                } while ((bh = next_bh) != NULL);

                mempool_free(ioend, xfs_ioend_pool);
        } while ((ioend = next) != NULL);
}

/*
 * Test to see if we've been building up a completion structure for
 * earlier buffers -- if so, we try to append to this ioend if we
 * can, otherwise we finish off any current ioend and start another.
 * Return true if we've finished the given ioend.
 */
STATIC void
xfs_add_to_ioend(
        struct inode            *inode,
        struct buffer_head      *bh,
        xfs_off_t               offset,
        unsigned int            type,
        xfs_ioend_t             **result,
        int                     need_ioend)
{
        xfs_ioend_t             *ioend = *result;

        if (!ioend || need_ioend || type != ioend->io_type) {
                xfs_ioend_t     *previous = *result;

                ioend = xfs_alloc_ioend(inode, type);
                ioend->io_offset = offset;
                ioend->io_buffer_head = bh;
                ioend->io_buffer_tail = bh;
                if (previous)
                        previous->io_list = ioend;
                *result = ioend;
        } else {
                ioend->io_buffer_tail->b_private = bh;
                ioend->io_buffer_tail = bh;
        }

        bh->b_private = NULL;
        ioend->io_size += bh->b_size;
}

STATIC void
xfs_map_buffer(
        struct inode            *inode,
        struct buffer_head      *bh,
        struct xfs_bmbt_irec    *imap,
        xfs_off_t               offset)
{
        sector_t                bn;
        struct xfs_mount        *m = XFS_I(inode)->i_mount;
        xfs_off_t               iomap_offset = XFS_FSB_TO_B(m, imap->br_startoff);
        xfs_daddr_t             iomap_bn = xfs_fsb_to_db(XFS_I(inode), imap->br_startblock);

        ASSERT(imap->br_startblock != HOLESTARTBLOCK);
        ASSERT(imap->br_startblock != DELAYSTARTBLOCK);

        bn = (iomap_bn >> (inode->i_blkbits - BBSHIFT)) +
              ((offset - iomap_offset) >> inode->i_blkbits);

        ASSERT(bn || XFS_IS_REALTIME_INODE(XFS_I(inode)));

        bh->b_blocknr = bn;
        set_buffer_mapped(bh);
}

STATIC void
xfs_map_at_offset(
        struct inode            *inode,
        struct buffer_head      *bh,
        struct xfs_bmbt_irec    *imap,
        xfs_off_t               offset)
{
        ASSERT(imap->br_startblock != HOLESTARTBLOCK);
        ASSERT(imap->br_startblock != DELAYSTARTBLOCK);

        xfs_map_buffer(inode, bh, imap, offset);
        set_buffer_mapped(bh);
        clear_buffer_delay(bh);
        clear_buffer_unwritten(bh);
}

/*
 * Test if a given page contains at least one buffer of a given @type.
 * If @check_all_buffers is true, then we walk all the buffers in the page to
 * try to find one of the type passed in. If it is not set, then the caller only
 * needs to check the first buffer on the page for a match.
 */
STATIC bool
xfs_check_page_type(
        struct page             *page,
        unsigned int            type,
        bool                    check_all_buffers)
{
        struct buffer_head      *bh;
        struct buffer_head      *head;

        if (PageWriteback(page))
                return false;
        if (!page->mapping)
                return false;
        if (!page_has_buffers(page))
                return false;

        bh = head = page_buffers(page);
        do {
                if (buffer_unwritten(bh)) {
                        if (type == XFS_IO_UNWRITTEN)
                                return true;
                } else if (buffer_delay(bh)) {
                        if (type == XFS_IO_DELALLOC)
                                return true;
                } else if (buffer_dirty(bh) && buffer_mapped(bh)) {
                        if (type == XFS_IO_OVERWRITE)
                                return true;
                }

                /* If we are only checking the first buffer, we are done now. */
                if (!check_all_buffers)
                        break;
        } while ((bh = bh->b_this_page) != head);

        return false;
}

/*
 * Allocate & map buffers for page given the extent map. Write it out.
 * except for the original page of a writepage, this is called on
 * delalloc/unwritten pages only, for the original page it is possible
 * that the page has no mapping at all.
 */
STATIC int
xfs_convert_page(
        struct inode            *inode,
        struct page             *page,
        loff_t                  tindex,
        struct xfs_bmbt_irec    *imap,
        xfs_ioend_t             **ioendp,
        struct writeback_control *wbc)
{
        struct buffer_head      *bh, *head;
        xfs_off_t               end_offset;
        unsigned long           p_offset;
        unsigned int            type;
        int                     len, page_dirty;
        int                     count = 0, done = 0, uptodate = 1;
        xfs_off_t               offset = page_offset(page);

        if (page->index != tindex)
                goto fail;
        if (!trylock_page(page))
                goto fail;
        if (PageWriteback(page))
                goto fail_unlock_page;
        if (page->mapping != inode->i_mapping)
                goto fail_unlock_page;
        if (!xfs_check_page_type(page, (*ioendp)->io_type, false))
                goto fail_unlock_page;

        /*
         * page_dirty is initially a count of buffers on the page before
         * EOF and is decremented as we move each into a cleanable state.
         *
         * Derivation:
         *
         * End offset is the highest offset that this page should represent.
         * If we are on the last page, (end_offset & (PAGE_CACHE_SIZE - 1))
         * will evaluate non-zero and be less than PAGE_CACHE_SIZE and
         * hence give us the correct page_dirty count. On any other page,
         * it will be zero and in that case we need page_dirty to be the
         * count of buffers on the page.
         */
        end_offset = min_t(unsigned long long,
                        (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT,
                        i_size_read(inode));

        /*
         * If the current map does not span the entire page we are about to try
         * to write, then give up. The only way we can write a page that spans
         * multiple mappings in a single writeback iteration is via the
         * xfs_vm_writepage() function. Data integrity writeback requires the
         * entire page to be written in a single attempt, otherwise the part of
         * the page we don't write here doesn't get written as part of the data
         * integrity sync.
         *
         * For normal writeback, we also don't attempt to write partial pages
         * here as it simply means that write_cache_pages() will see it under
         * writeback and ignore the page until some point in the future, at
         * which time this will be the only page in the file that needs
         * writeback.  Hence for more optimal IO patterns, we should always
         * avoid partial page writeback due to multiple mappings on a page here.
         */
        if (!xfs_imap_valid(inode, imap, end_offset))
                goto fail_unlock_page;

        len = 1 << inode->i_blkbits;
        p_offset = min_t(unsigned long, end_offset & (PAGE_CACHE_SIZE - 1),
                                        PAGE_CACHE_SIZE);
        p_offset = p_offset ? roundup(p_offset, len) : PAGE_CACHE_SIZE;
        page_dirty = p_offset / len;

        /*
         * The moment we find a buffer that doesn't match our current type
         * specification or can't be written, abort the loop and start
         * writeback. As per the above xfs_imap_valid() check, only
         * xfs_vm_writepage() can handle partial page writeback fully - we are
         * limited here to the buffers that are contiguous with the current
         * ioend, and hence a buffer we can't write breaks that contiguity and
         * we have to defer the rest of the IO to xfs_vm_writepage().
         */
        bh = head = page_buffers(page);
        do {
                if (offset >= end_offset)
                        break;
                if (!buffer_uptodate(bh))
                        uptodate = 0;
                if (!(PageUptodate(page) || buffer_uptodate(bh))) {
                        done = 1;
                        break;
                }

                if (buffer_unwritten(bh) || buffer_delay(bh) ||
                    buffer_mapped(bh)) {
                        if (buffer_unwritten(bh))
                                type = XFS_IO_UNWRITTEN;
                        else if (buffer_delay(bh))
                                type = XFS_IO_DELALLOC;
                        else
                                type = XFS_IO_OVERWRITE;

                        /*
                         * imap should always be valid because of the above
                         * partial page end_offset check on the imap.
                         */
                        ASSERT(xfs_imap_valid(inode, imap, offset));

                        lock_buffer(bh);
                        if (type != XFS_IO_OVERWRITE)
                                xfs_map_at_offset(inode, bh, imap, offset);
                        xfs_add_to_ioend(inode, bh, offset, type,
                                         ioendp, done);

                        page_dirty--;
                        count++;
                } else {
                        done = 1;
                        break;
                }
        } while (offset += len, (bh = bh->b_this_page) != head);

        if (uptodate && bh == head)
                SetPageUptodate(page);

        if (count) {
                if (--wbc->nr_to_write <= 0 &&
                    wbc->sync_mode == WB_SYNC_NONE)
                        done = 1;
        }
        xfs_start_page_writeback(page, !page_dirty, count);

        return done;
 fail_unlock_page:
        unlock_page(page);
 fail:
        return 1;
}

/*
 * Convert & write out a cluster of pages in the same extent as defined
 * by mp and following the start page.
 */
STATIC void
xfs_cluster_write(
        struct inode            *inode,
        pgoff_t                 tindex,
        struct xfs_bmbt_irec    *imap,
        xfs_ioend_t             **ioendp,
        struct writeback_control *wbc,
        pgoff_t                 tlast)
{
        struct pagevec          pvec;
        int                     done = 0, i;

        pagevec_init(&pvec, 0);
        while (!done && tindex <= tlast) {
                unsigned len = min_t(pgoff_t, PAGEVEC_SIZE, tlast - tindex + 1);

                if (!pagevec_lookup(&pvec, inode->i_mapping, tindex, len))
                        break;

                for (i = 0; i < pagevec_count(&pvec); i++) {
                        done = xfs_convert_page(inode, pvec.pages[i], tindex++,
                                        imap, ioendp, wbc);
                        if (done)
                                break;
                }

                pagevec_release(&pvec);
                cond_resched();
        }
}

STATIC void
xfs_vm_invalidatepage(
        struct page             *page,
        unsigned int            offset,
        unsigned int            length)
{
        trace_xfs_invalidatepage(page->mapping->host, page, offset,
                                 length);
        block_invalidatepage(page, offset, length);
}

/*
 * If the page has delalloc buffers on it, we need to punch them out before we
 * invalidate the page. If we don't, we leave a stale delalloc mapping on the
 * inode that can trip a BUG() in xfs_get_blocks() later on if a direct IO read
 * is done on that same region - the delalloc extent is returned when none is
 * supposed to be there.
 *
 * We prevent this by truncating away the delalloc regions on the page before
 * invalidating it. Because they are delalloc, we can do this without needing a
 * transaction. Indeed - if we get ENOSPC errors, we have to be able to do this
 * truncation without a transaction as there is no space left for block
 * reservation (typically why we see a ENOSPC in writeback).
 *
 * This is not a performance critical path, so for now just do the punching a
 * buffer head at a time.
 */
STATIC void
xfs_aops_discard_page(
        struct page             *page)
{
        struct inode            *inode = page->mapping->host;
        struct xfs_inode        *ip = XFS_I(inode);
        struct buffer_head      *bh, *head;
        loff_t                  offset = page_offset(page);

        if (!xfs_check_page_type(page, XFS_IO_DELALLOC, true))
                goto out_invalidate;

        if (XFS_FORCED_SHUTDOWN(ip->i_mount))
                goto out_invalidate;

        xfs_alert(ip->i_mount,
                "page discard on page %p, inode 0x%llx, offset %llu.",
                        page, ip->i_ino, offset);

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        bh = head = page_buffers(page);
        do {
                int             error;
                xfs_fileoff_t   start_fsb;

                if (!buffer_delay(bh))
                        goto next_buffer;

                start_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
                error = xfs_bmap_punch_delalloc_range(ip, start_fsb, 1);
                if (error) {
                        /* something screwed, just bail */
                        if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                                xfs_alert(ip->i_mount,
                        "page discard unable to remove delalloc mapping.");
                        }
                        break;
                }
next_buffer:
                offset += 1 << inode->i_blkbits;

        } while ((bh = bh->b_this_page) != head);

        xfs_iunlock(ip, XFS_ILOCK_EXCL);
out_invalidate:
        xfs_vm_invalidatepage(page, 0, PAGE_CACHE_SIZE);
        return;
}

/*
 * Write out a dirty page.
 *
 * For delalloc space on the page we need to allocate space and flush it.
 * For unwritten space on the page we need to start the conversion to
 * regular allocated space.
 * For any other dirty buffer heads on the page we should flush them.
 */
STATIC int
xfs_vm_writepage(
        struct page             *page,
        struct writeback_control *wbc)
{
        struct inode            *inode = page->mapping->host;
        struct buffer_head      *bh, *head;
        struct xfs_bmbt_irec    imap;
        xfs_ioend_t             *ioend = NULL, *iohead = NULL;
        loff_t                  offset;
        unsigned int            type;
        __uint64_t              end_offset;
        pgoff_t                 end_index, last_index;
        ssize_t                 len;
        int                     err, imap_valid = 0, uptodate = 1;
        int                     count = 0;
        int                     nonblocking = 0;

        trace_xfs_writepage(inode, page, 0, 0);

        ASSERT(page_has_buffers(page));

        /*
         * Refuse to write the page out if we are called from reclaim context.
         *
         * This avoids stack overflows when called from deeply used stacks in
         * random callers for direct reclaim or memcg reclaim.  We explicitly
         * allow reclaim from kswapd as the stack usage there is relatively low.
         *
         * This should never happen except in the case of a VM regression so
         * warn about it.
         */
        if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
                        PF_MEMALLOC))
                goto redirty;

        /*
         * Given that we do not allow direct reclaim to call us, we should
         * never be called while in a filesystem transaction.
         */
        if (WARN_ON(current->flags & PF_FSTRANS))
                goto redirty;

        /* Is this page beyond the end of the file? */
        offset = i_size_read(inode);
        end_index = offset >> PAGE_CACHE_SHIFT;
        last_index = (offset - 1) >> PAGE_CACHE_SHIFT;
        if (page->index >= end_index) {
                unsigned offset_into_page = offset & (PAGE_CACHE_SIZE - 1);

                /*
                 * Skip the page if it is fully outside i_size, e.g. due to a
                 * truncate operation that is in progress. We must redirty the
                 * page so that reclaim stops reclaiming it. Otherwise
                 * xfs_vm_releasepage() is called on it and gets confused.
                 */
                if (page->index >= end_index + 1 || offset_into_page == 0)
                        goto redirty;

                /*
                 * The page straddles i_size.  It must be zeroed out on each
                 * and every writepage invocation because it may be mmapped.
                 * "A file is mapped in multiples of the page size.  For a file
                 * that is not a multiple of the  page size, the remaining
                 * memory is zeroed when mapped, and writes to that region are
                 * not written out to the file."
                 */
                zero_user_segment(page, offset_into_page, PAGE_CACHE_SIZE);
        }

        end_offset = min_t(unsigned long long,
                        (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT,
                        offset);
        len = 1 << inode->i_blkbits;

        bh = head = page_buffers(page);
        offset = page_offset(page);
        type = XFS_IO_OVERWRITE;

        if (wbc->sync_mode == WB_SYNC_NONE)
                nonblocking = 1;

        do {
                int new_ioend = 0;

                if (offset >= end_offset)
                        break;
                if (!buffer_uptodate(bh))
                        uptodate = 0;

                /*
                 * set_page_dirty dirties all buffers in a page, independent
                 * of their state.  The dirty state however is entirely
                 * meaningless for holes (!mapped && uptodate), so skip
                 * buffers covering holes here.
                 */
                if (!buffer_mapped(bh) && buffer_uptodate(bh)) {
                        imap_valid = 0;
                        continue;
                }

                if (buffer_unwritten(bh)) {
                        if (type != XFS_IO_UNWRITTEN) {
                                type = XFS_IO_UNWRITTEN;
                                imap_valid = 0;
                        }
                } else if (buffer_delay(bh)) {
                        if (type != XFS_IO_DELALLOC) {
                                type = XFS_IO_DELALLOC;
                                imap_valid = 0;
                        }
                } else if (buffer_uptodate(bh)) {
                        if (type != XFS_IO_OVERWRITE) {
                                type = XFS_IO_OVERWRITE;
                                imap_valid = 0;
                        }
                } else {
                        if (PageUptodate(page))
                                ASSERT(buffer_mapped(bh));
                        /*
                         * This buffer is not uptodate and will not be
                         * written to disk.  Ensure that we will put any
                         * subsequent writeable buffers into a new
                         * ioend.
                         */
                        imap_valid = 0;
                        continue;
                }

                if (imap_valid)
                        imap_valid = xfs_imap_valid(inode, &imap, offset);
                if (!imap_valid) {
                        /*
                         * If we didn't have a valid mapping then we need to
                         * put the new mapping into a separate ioend structure.
                         * This ensures non-contiguous extents always have
                         * separate ioends, which is particularly important
                         * for unwritten extent conversion at I/O completion
                         * time.
                         */
                        new_ioend = 1;
                        err = xfs_map_blocks(inode, offset, &imap, type,
                                             nonblocking);
                        if (err)
                                goto error;
                        imap_valid = xfs_imap_valid(inode, &imap, offset);
                }
                if (imap_valid) {
                        lock_buffer(bh);
                        if (type != XFS_IO_OVERWRITE)
                                xfs_map_at_offset(inode, bh, &imap, offset);
                        xfs_add_to_ioend(inode, bh, offset, type, &ioend,
                                         new_ioend);
                        count++;
                }

                if (!iohead)
                        iohead = ioend;

        } while (offset += len, ((bh = bh->b_this_page) != head));

        if (uptodate && bh == head)
                SetPageUptodate(page);

        xfs_start_page_writeback(page, 1, count);

        /* if there is no IO to be submitted for this page, we are done */
        if (!ioend)
                return 0;

        ASSERT(iohead);

        /*
         * Any errors from this point onwards need tobe reported through the IO
         * completion path as we have marked the initial page as under writeback
         * and unlocked it.
         */
        if (imap_valid) {
                xfs_off_t               end_index;

                end_index = imap.br_startoff + imap.br_blockcount;

                /* to bytes */
                end_index <<= inode->i_blkbits;

                /* to pages */
                end_index = (end_index - 1) >> PAGE_CACHE_SHIFT;

                /* check against file size */
                if (end_index > last_index)
                        end_index = last_index;

                xfs_cluster_write(inode, page->index + 1, &imap, &ioend,
                                  wbc, end_index);
        }


        /*
         * Reserve log space if we might write beyond the on-disk inode size.
         */
        err = 0;
        if (ioend->io_type != XFS_IO_UNWRITTEN && xfs_ioend_is_append(ioend))
                err = xfs_setfilesize_trans_alloc(ioend);

        xfs_submit_ioend(wbc, iohead, err);

        return 0;

error:
        if (iohead)
                xfs_cancel_ioend(iohead);

        if (err == -EAGAIN)
                goto redirty;

        xfs_aops_discard_page(page);
        ClearPageUptodate(page);
        unlock_page(page);
        return err;

redirty:
        redirty_page_for_writepage(wbc, page);
        unlock_page(page);
        return 0;
}

STATIC int
xfs_vm_writepages(
        struct address_space    *mapping,
        struct writeback_control *wbc)
{
        xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
        return generic_writepages(mapping, wbc);
}

/*
 * Called to move a page into cleanable state - and from there
 * to be released. The page should already be clean. We always
 * have buffer heads in this call.
 *
 * Returns 1 if the page is ok to release, 0 otherwise.
 */
STATIC int
xfs_vm_releasepage(
        struct page             *page,
        gfp_t                   gfp_mask)
{
        int                     delalloc, unwritten;

        trace_xfs_releasepage(page->mapping->host, page, 0, 0);

        xfs_count_page_state(page, &delalloc, &unwritten);

        if (WARN_ON(delalloc))
                return 0;
        if (WARN_ON(unwritten))
                return 0;

        return try_to_free_buffers(page);
}

STATIC int
__xfs_get_blocks(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create,
        int                     direct)
{
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
        xfs_fileoff_t           offset_fsb, end_fsb;
        int                     error = 0;
        int                     lockmode = 0;
        struct xfs_bmbt_irec    imap;
        int                     nimaps = 1;
        xfs_off_t               offset;
        ssize_t                 size;
        int                     new = 0;

        if (XFS_FORCED_SHUTDOWN(mp))
                return -XFS_ERROR(EIO);

        offset = (xfs_off_t)iblock << inode->i_blkbits;
        ASSERT(bh_result->b_size >= (1 << inode->i_blkbits));
        size = bh_result->b_size;

        if (!create && direct && offset >= i_size_read(inode))
                return 0;

        /*
         * Direct I/O is usually done on preallocated files, so try getting
         * a block mapping without an exclusive lock first.  For buffered
         * writes we already have the exclusive iolock anyway, so avoiding
         * a lock roundtrip here by taking the ilock exclusive from the
         * beginning is a useful micro optimization.
         */
        if (create && !direct) {
                lockmode = XFS_ILOCK_EXCL;
                xfs_ilock(ip, lockmode);
        } else {
                lockmode = xfs_ilock_data_map_shared(ip);
        }

        ASSERT(offset <= mp->m_super->s_maxbytes);
        if (offset + size > mp->m_super->s_maxbytes)
                size = mp->m_super->s_maxbytes - offset;
        end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + size);
        offset_fsb = XFS_B_TO_FSBT(mp, offset);

        error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
                                &imap, &nimaps, XFS_BMAPI_ENTIRE);
        if (error)
                goto out_unlock;

        if (create &&
            (!nimaps ||
             (imap.br_startblock == HOLESTARTBLOCK ||
              imap.br_startblock == DELAYSTARTBLOCK))) {
                if (direct || xfs_get_extsz_hint(ip)) {
                        /*
                         * Drop the ilock in preparation for starting the block
                         * allocation transaction.  It will be retaken
                         * exclusively inside xfs_iomap_write_direct for the
                         * actual allocation.
                         */
                        xfs_iunlock(ip, lockmode);
                        error = xfs_iomap_write_direct(ip, offset, size,
                                                       &imap, nimaps);
                        if (error)
                                return -error;
                        new = 1;
                } else {
                        /*
                         * Delalloc reservations do not require a transaction,
                         * we can go on without dropping the lock here. If we
                         * are allocating a new delalloc block, make sure that
                         * we set the new flag so that we mark the buffer new so
                         * that we know that it is newly allocated if the write
                         * fails.
                         */
                        if (nimaps && imap.br_startblock == HOLESTARTBLOCK)
                                new = 1;
                        error = xfs_iomap_write_delay(ip, offset, size, &imap);
                        if (error)
                                goto out_unlock;

                        xfs_iunlock(ip, lockmode);
                }

                trace_xfs_get_blocks_alloc(ip, offset, size, 0, &imap);
        } else if (nimaps) {
                trace_xfs_get_blocks_found(ip, offset, size, 0, &imap);
                xfs_iunlock(ip, lockmode);
        } else {
                trace_xfs_get_blocks_notfound(ip, offset, size);
                goto out_unlock;
        }

        if (imap.br_startblock != HOLESTARTBLOCK &&
            imap.br_startblock != DELAYSTARTBLOCK) {
                /*
                 * For unwritten extents do not report a disk address on
                 * the read case (treat as if we're reading into a hole).
                 */
                if (create || !ISUNWRITTEN(&imap))
                        xfs_map_buffer(inode, bh_result, &imap, offset);
                if (create && ISUNWRITTEN(&imap)) {
                        if (direct) {
                                bh_result->b_private = inode;
                                set_buffer_defer_completion(bh_result);
                        }
                        set_buffer_unwritten(bh_result);
                }
        }

        /*
         * If this is a realtime file, data may be on a different device.
         * to that pointed to from the buffer_head b_bdev currently.
         */
        bh_result->b_bdev = xfs_find_bdev_for_inode(inode);

        /*
         * If we previously allocated a block out beyond eof and we are now
         * coming back to use it then we will need to flag it as new even if it
         * has a disk address.
         *
         * With sub-block writes into unwritten extents we also need to mark
         * the buffer as new so that the unwritten parts of the buffer gets
         * correctly zeroed.
         */
        if (create &&
            ((!buffer_mapped(bh_result) && !buffer_uptodate(bh_result)) ||
             (offset >= i_size_read(inode)) ||
             (new || ISUNWRITTEN(&imap))))
                set_buffer_new(bh_result);

        if (imap.br_startblock == DELAYSTARTBLOCK) {
                BUG_ON(direct);
                if (create) {
                        set_buffer_uptodate(bh_result);
                        set_buffer_mapped(bh_result);
                        set_buffer_delay(bh_result);
                }
        }

        /*
         * If this is O_DIRECT or the mpage code calling tell them how large
         * the mapping is, so that we can avoid repeated get_blocks calls.
         *
         * If the mapping spans EOF, then we have to break the mapping up as the
         * mapping for blocks beyond EOF must be marked new so that sub block
         * regions can be correctly zeroed. We can't do this for mappings within
         * EOF unless the mapping was just allocated or is unwritten, otherwise
         * the callers would overwrite existing data with zeros. Hence we have
         * to split the mapping into a range up to and including EOF, and a
         * second mapping for beyond EOF.
         */
        if (direct || size > (1 << inode->i_blkbits)) {
                xfs_off_t               mapping_size;

                mapping_size = imap.br_startoff + imap.br_blockcount - iblock;
                mapping_size <<= inode->i_blkbits;

                ASSERT(mapping_size > 0);
                if (mapping_size > size)
                        mapping_size = size;
                if (offset < i_size_read(inode) &&
                    offset + mapping_size >= i_size_read(inode)) {
                        /* limit mapping to block that spans EOF */
                        mapping_size = roundup_64(i_size_read(inode) - offset,
                                                  1 << inode->i_blkbits);
                }
                if (mapping_size > LONG_MAX)
                        mapping_size = LONG_MAX;

                bh_result->b_size = mapping_size;
        }

        return 0;

out_unlock:
        xfs_iunlock(ip, lockmode);
        return -error;
}

int
xfs_get_blocks(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create)
{
        return __xfs_get_blocks(inode, iblock, bh_result, create, 0);
}

STATIC int
xfs_get_blocks_direct(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create)
{
        return __xfs_get_blocks(inode, iblock, bh_result, create, 1);
}

/*
 * Complete a direct I/O write request.
 *
 * If the private argument is non-NULL __xfs_get_blocks signals us that we
 * need to issue a transaction to convert the range from unwritten to written
 * extents.  In case this is regular synchronous I/O we just call xfs_end_io
 * to do this and we are done.  But in case this was a successful AIO
 * request this handler is called from interrupt context, from which we
 * can't start transactions.  In that case offload the I/O completion to
 * the workqueues we also use for buffered I/O completion.
 */
STATIC void
xfs_end_io_direct_write(
        struct kiocb            *iocb,
        loff_t                  offset,
        ssize_t                 size,
        void                    *private)
{
        struct xfs_ioend        *ioend = iocb->private;

        /*
         * While the generic direct I/O code updates the inode size, it does
         * so only after the end_io handler is called, which means our
         * end_io handler thinks the on-disk size is outside the in-core
         * size.  To prevent this just update it a little bit earlier here.
         */
        if (offset + size > i_size_read(ioend->io_inode))
                i_size_write(ioend->io_inode, offset + size);

        /*
         * blockdev_direct_IO can return an error even after the I/O
         * completion handler was called.  Thus we need to protect
         * against double-freeing.
         */
        iocb->private = NULL;

        ioend->io_offset = offset;
        ioend->io_size = size;
        if (private && size > 0)
                ioend->io_type = XFS_IO_UNWRITTEN;

        xfs_finish_ioend_sync(ioend);
}

STATIC ssize_t
xfs_vm_direct_IO(
        int                     rw,
        struct kiocb            *iocb,
        const struct iovec      *iov,
        loff_t                  offset,
        unsigned long           nr_segs)
{
        struct inode            *inode = iocb->ki_filp->f_mapping->host;
        struct block_device     *bdev = xfs_find_bdev_for_inode(inode);
        struct xfs_ioend        *ioend = NULL;
        ssize_t                 ret;

        if (rw & WRITE) {
                size_t size = iov_length(iov, nr_segs);

                /*
                 * We cannot preallocate a size update transaction here as we
                 * don't know whether allocation is necessary or not. Hence we
                 * can only tell IO completion that one is necessary if we are
                 * not doing unwritten extent conversion.
                 */
                iocb->private = ioend = xfs_alloc_ioend(inode, XFS_IO_DIRECT);
                if (offset + size > XFS_I(inode)->i_d.di_size)
                        ioend->io_isdirect = 1;

                ret = __blockdev_direct_IO(rw, iocb, inode, bdev, iov,
                                            offset, nr_segs,
                                            xfs_get_blocks_direct,
                                            xfs_end_io_direct_write, NULL,
                                            DIO_ASYNC_EXTEND);
                if (ret != -EIOCBQUEUED && iocb->private)
                        goto out_destroy_ioend;
        } else {
                ret = __blockdev_direct_IO(rw, iocb, inode, bdev, iov,
                                            offset, nr_segs,
                                            xfs_get_blocks_direct,
                                            NULL, NULL, 0);
        }

        return ret;

out_destroy_ioend:
        xfs_destroy_ioend(ioend);
        return ret;
}

/*
 * Punch out the delalloc blocks we have already allocated.
 *
 * Don't bother with xfs_setattr given that nothing can have made it to disk yet
 * as the page is still locked at this point.
 */
STATIC void
xfs_vm_kill_delalloc_range(
        struct inode            *inode,
        loff_t                  start,
        loff_t                  end)
{
        struct xfs_inode        *ip = XFS_I(inode);
        xfs_fileoff_t           start_fsb;
        xfs_fileoff_t           end_fsb;
        int                     error;

        start_fsb = XFS_B_TO_FSB(ip->i_mount, start);
        end_fsb = XFS_B_TO_FSB(ip->i_mount, end);
        if (end_fsb <= start_fsb)
                return;

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        error = xfs_bmap_punch_delalloc_range(ip, start_fsb,
                                                end_fsb - start_fsb);
        if (error) {
                /* something screwed, just bail */
                if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                        xfs_alert(ip->i_mount,
                "xfs_vm_write_failed: unable to clean up ino %lld",
                                        ip->i_ino);
                }
        }
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
}

STATIC void
xfs_vm_write_failed(
        struct inode            *inode,
        struct page             *page,
        loff_t                  pos,
        unsigned                len)
{
        loff_t                  block_offset;
        loff_t                  block_start;
        loff_t                  block_end;
        loff_t                  from = pos & (PAGE_CACHE_SIZE - 1);
        loff_t                  to = from + len;
        struct buffer_head      *bh, *head;

        /*
         * The request pos offset might be 32 or 64 bit, this is all fine
         * on 64-bit platform.  However, for 64-bit pos request on 32-bit
         * platform, the high 32-bit will be masked off if we evaluate the
         * block_offset via (pos & PAGE_MASK) because the PAGE_MASK is
         * 0xfffff000 as an unsigned long, hence the result is incorrect
         * which could cause the following ASSERT failed in most cases.
         * In order to avoid this, we can evaluate the block_offset of the
         * start of the page by using shifts rather than masks the mismatch
         * problem.
         */
        block_offset = (pos >> PAGE_CACHE_SHIFT) << PAGE_CACHE_SHIFT;

        ASSERT(block_offset + from == pos);

        head = page_buffers(page);
        block_start = 0;
        for (bh = head; bh != head || !block_start;
             bh = bh->b_this_page, block_start = block_end,
                                   block_offset += bh->b_size) {
                block_end = block_start + bh->b_size;

                /* skip buffers before the write */
                if (block_end <= from)
                        continue;

                /* if the buffer is after the write, we're done */
                if (block_start >= to)
                        break;

                if (!buffer_delay(bh))
                        continue;

                if (!buffer_new(bh) && block_offset < i_size_read(inode))
                        continue;

                xfs_vm_kill_delalloc_range(inode, block_offset,
                                           block_offset + bh->b_size);

                /*
                 * This buffer does not contain data anymore. make sure anyone
                 * who finds it knows that for certain.
                 */
                clear_buffer_delay(bh);
                clear_buffer_uptodate(bh);
                clear_buffer_mapped(bh);
                clear_buffer_new(bh);
                clear_buffer_dirty(bh);
        }

}

/*
 * This used to call block_write_begin(), but it unlocks and releases the page
 * on error, and we need that page to be able to punch stale delalloc blocks out
 * on failure. hence we copy-n-waste it here and call xfs_vm_write_failed() at
 * the appropriate point.
 */
STATIC int
xfs_vm_write_begin(
        struct file             *file,
        struct address_space    *mapping,
        loff_t                  pos,
        unsigned                len,
        unsigned                flags,
        struct page             **pagep,
        void                    **fsdata)
{
        pgoff_t                 index = pos >> PAGE_CACHE_SHIFT;
        struct page             *page;
        int                     status;

        ASSERT(len <= PAGE_CACHE_SIZE);

        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page)
                return -ENOMEM;

        status = __block_write_begin(page, pos, len, xfs_get_blocks);
        if (unlikely(status)) {
                struct inode    *inode = mapping->host;
                size_t          isize = i_size_read(inode);

                xfs_vm_write_failed(inode, page, pos, len);
                unlock_page(page);

                /*
                 * If the write is beyond EOF, we only want to kill blocks
                 * allocated in this write, not blocks that were previously
                 * written successfully.
                 */
                if (pos + len > isize) {
                        ssize_t start = max_t(ssize_t, pos, isize);

                        truncate_pagecache_range(inode, start, pos + len);
                }

                page_cache_release(page);
                page = NULL;
        }

        *pagep = page;
        return status;
}

/*
 * On failure, we only need to kill delalloc blocks beyond EOF in the range of
 * this specific write because they will never be written. Previous writes
 * beyond EOF where block allocation succeeded do not need to be trashed, so
 * only new blocks from this write should be trashed. For blocks within
 * EOF, generic_write_end() zeros them so they are safe to leave alone and be
 * written with all the other valid data.
 */
STATIC int
xfs_vm_write_end(
        struct file             *file,
        struct address_space    *mapping,
        loff_t                  pos,
        unsigned                len,
        unsigned                copied,
        struct page             *page,
        void                    *fsdata)
{
        int                     ret;

        ASSERT(len <= PAGE_CACHE_SIZE);

        ret = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
        if (unlikely(ret < len)) {
                struct inode    *inode = mapping->host;
                size_t          isize = i_size_read(inode);
                loff_t          to = pos + len;

                if (to > isize) {
                        /* only kill blocks in this write beyond EOF */
                        if (pos > isize)
                                isize = pos;
                        xfs_vm_kill_delalloc_range(inode, isize, to);
                        truncate_pagecache_range(inode, isize, to);
                }
        }
        return ret;
}

STATIC sector_t
xfs_vm_bmap(
        struct address_space    *mapping,
        sector_t                block)
{
        struct inode            *inode = (struct inode *)mapping->host;
        struct xfs_inode        *ip = XFS_I(inode);

        trace_xfs_vm_bmap(XFS_I(inode));
        xfs_ilock(ip, XFS_IOLOCK_SHARED);
        filemap_write_and_wait(mapping);
        xfs_iunlock(ip, XFS_IOLOCK_SHARED);
        return generic_block_bmap(mapping, block, xfs_get_blocks);
}

STATIC int
xfs_vm_readpage(
        struct file             *unused,
        struct page             *page)
{
        return mpage_readpage(page, xfs_get_blocks);
}

STATIC int
xfs_vm_readpages(
        struct file             *unused,
        struct address_space    *mapping,
        struct list_head        *pages,
        unsigned                nr_pages)
{
        return mpage_readpages(mapping, pages, nr_pages, xfs_get_blocks);
}

const struct address_space_operations xfs_address_space_operations = {
        .readpage               = xfs_vm_readpage,
        .readpages              = xfs_vm_readpages,
        .writepage              = xfs_vm_writepage,
        .writepages             = xfs_vm_writepages,
        .releasepage            = xfs_vm_releasepage,
        .invalidatepage         = xfs_vm_invalidatepage,
        .write_begin            = xfs_vm_write_begin,
        .write_end              = xfs_vm_write_end,
        .bmap                   = xfs_vm_bmap,
        .direct_IO              = xfs_vm_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
        .error_remove_page      = generic_error_remove_page,
};