initial commit with v2.6.32.60

[linux-2.6.32.60-moxart.git] / fs / btrfs / ordered-data.c

/*
 * Copyright (C) 2007 Oracle.  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 v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will 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 to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include "ctree.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "extent_io.h"

static u64 entry_end(struct btrfs_ordered_extent *entry)
{
        if (entry->file_offset + entry->len < entry->file_offset)
                return (u64)-1;
        return entry->file_offset + entry->len;
}

/* returns NULL if the insertion worked, or it returns the node it did find
 * in the tree
 */
static struct rb_node *tree_insert(struct rb_root *root, u64 file_offset,
                                   struct rb_node *node)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct btrfs_ordered_extent *entry;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct btrfs_ordered_extent, rb_node);

                if (file_offset < entry->file_offset)
                        p = &(*p)->rb_left;
                else if (file_offset >= entry_end(entry))
                        p = &(*p)->rb_right;
                else
                        return parent;
        }

        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
        return NULL;
}

/*
 * look for a given offset in the tree, and if it can't be found return the
 * first lesser offset
 */
static struct rb_node *__tree_search(struct rb_root *root, u64 file_offset,
                                     struct rb_node **prev_ret)
{
        struct rb_node *n = root->rb_node;
        struct rb_node *prev = NULL;
        struct rb_node *test;
        struct btrfs_ordered_extent *entry;
        struct btrfs_ordered_extent *prev_entry = NULL;

        while (n) {
                entry = rb_entry(n, struct btrfs_ordered_extent, rb_node);
                prev = n;
                prev_entry = entry;

                if (file_offset < entry->file_offset)
                        n = n->rb_left;
                else if (file_offset >= entry_end(entry))
                        n = n->rb_right;
                else
                        return n;
        }
        if (!prev_ret)
                return NULL;

        while (prev && file_offset >= entry_end(prev_entry)) {
                test = rb_next(prev);
                if (!test)
                        break;
                prev_entry = rb_entry(test, struct btrfs_ordered_extent,
                                      rb_node);
                if (file_offset < entry_end(prev_entry))
                        break;

                prev = test;
        }
        if (prev)
                prev_entry = rb_entry(prev, struct btrfs_ordered_extent,
                                      rb_node);
        while (prev && file_offset < entry_end(prev_entry)) {
                test = rb_prev(prev);
                if (!test)
                        break;
                prev_entry = rb_entry(test, struct btrfs_ordered_extent,
                                      rb_node);
                prev = test;
        }
        *prev_ret = prev;
        return NULL;
}

/*
 * helper to check if a given offset is inside a given entry
 */
static int offset_in_entry(struct btrfs_ordered_extent *entry, u64 file_offset)
{
        if (file_offset < entry->file_offset ||
            entry->file_offset + entry->len <= file_offset)
                return 0;
        return 1;
}

/*
 * look find the first ordered struct that has this offset, otherwise
 * the first one less than this offset
 */
static inline struct rb_node *tree_search(struct btrfs_ordered_inode_tree *tree,
                                          u64 file_offset)
{
        struct rb_root *root = &tree->tree;
        struct rb_node *prev;
        struct rb_node *ret;
        struct btrfs_ordered_extent *entry;

        if (tree->last) {
                entry = rb_entry(tree->last, struct btrfs_ordered_extent,
                                 rb_node);
                if (offset_in_entry(entry, file_offset))
                        return tree->last;
        }
        ret = __tree_search(root, file_offset, &prev);
        if (!ret)
                ret = prev;
        if (ret)
                tree->last = ret;
        return ret;
}

/* allocate and add a new ordered_extent into the per-inode tree.
 * file_offset is the logical offset in the file
 *
 * start is the disk block number of an extent already reserved in the
 * extent allocation tree
 *
 * len is the length of the extent
 *
 * The tree is given a single reference on the ordered extent that was
 * inserted.
 */
int btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
                             u64 start, u64 len, u64 disk_len, int type)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry;

        tree = &BTRFS_I(inode)->ordered_tree;
        entry = kzalloc(sizeof(*entry), GFP_NOFS);
        if (!entry)
                return -ENOMEM;

        mutex_lock(&tree->mutex);
        entry->file_offset = file_offset;
        entry->start = start;
        entry->len = len;
        entry->disk_len = disk_len;
        entry->bytes_left = len;
        entry->inode = inode;
        if (type != BTRFS_ORDERED_IO_DONE && type != BTRFS_ORDERED_COMPLETE)
                set_bit(type, &entry->flags);

        /* one ref for the tree */
        atomic_set(&entry->refs, 1);
        init_waitqueue_head(&entry->wait);
        INIT_LIST_HEAD(&entry->list);
        INIT_LIST_HEAD(&entry->root_extent_list);

        node = tree_insert(&tree->tree, file_offset,
                           &entry->rb_node);
        BUG_ON(node);

        spin_lock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);
        list_add_tail(&entry->root_extent_list,
                      &BTRFS_I(inode)->root->fs_info->ordered_extents);
        spin_unlock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);

        mutex_unlock(&tree->mutex);
        BUG_ON(node);
        return 0;
}

/*
 * Add a struct btrfs_ordered_sum into the list of checksums to be inserted
 * when an ordered extent is finished.  If the list covers more than one
 * ordered extent, it is split across multiples.
 */
int btrfs_add_ordered_sum(struct inode *inode,
                          struct btrfs_ordered_extent *entry,
                          struct btrfs_ordered_sum *sum)
{
        struct btrfs_ordered_inode_tree *tree;

        tree = &BTRFS_I(inode)->ordered_tree;
        mutex_lock(&tree->mutex);
        list_add_tail(&sum->list, &entry->list);
        mutex_unlock(&tree->mutex);
        return 0;
}

/*
 * this is used to account for finished IO across a given range
 * of the file.  The IO should not span ordered extents.  If
 * a given ordered_extent is completely done, 1 is returned, otherwise
 * 0.
 *
 * test_and_set_bit on a flag in the struct btrfs_ordered_extent is used
 * to make sure this function only returns 1 once for a given ordered extent.
 */
int btrfs_dec_test_ordered_pending(struct inode *inode,
                                   u64 file_offset, u64 io_size)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry;
        int ret;

        tree = &BTRFS_I(inode)->ordered_tree;
        mutex_lock(&tree->mutex);
        node = tree_search(tree, file_offset);
        if (!node) {
                ret = 1;
                goto out;
        }

        entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
        if (!offset_in_entry(entry, file_offset)) {
                ret = 1;
                goto out;
        }

        if (io_size > entry->bytes_left) {
                printk(KERN_CRIT "bad ordered accounting left %llu size %llu\n",
                       (unsigned long long)entry->bytes_left,
                       (unsigned long long)io_size);
        }
        entry->bytes_left -= io_size;
        if (entry->bytes_left == 0)
                ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
        else
                ret = 1;
out:
        mutex_unlock(&tree->mutex);
        return ret == 0;
}

/*
 * used to drop a reference on an ordered extent.  This will free
 * the extent if the last reference is dropped
 */
int btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry)
{
        struct list_head *cur;
        struct btrfs_ordered_sum *sum;

        if (atomic_dec_and_test(&entry->refs)) {
                while (!list_empty(&entry->list)) {
                        cur = entry->list.next;
                        sum = list_entry(cur, struct btrfs_ordered_sum, list);
                        list_del(&sum->list);
                        kfree(sum);
                }
                kfree(entry);
        }
        return 0;
}

/*
 * remove an ordered extent from the tree.  No references are dropped
 * and you must wake_up entry->wait.  You must hold the tree mutex
 * while you call this function.
 */
static int __btrfs_remove_ordered_extent(struct inode *inode,
                                struct btrfs_ordered_extent *entry)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;

        tree = &BTRFS_I(inode)->ordered_tree;
        node = &entry->rb_node;
        rb_erase(node, &tree->tree);
        tree->last = NULL;
        set_bit(BTRFS_ORDERED_COMPLETE, &entry->flags);

        spin_lock(&BTRFS_I(inode)->accounting_lock);
        BTRFS_I(inode)->outstanding_extents--;
        spin_unlock(&BTRFS_I(inode)->accounting_lock);
        btrfs_unreserve_metadata_for_delalloc(BTRFS_I(inode)->root,
                                              inode, 1);

        spin_lock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);
        list_del_init(&entry->root_extent_list);

        /*
         * we have no more ordered extents for this inode and
         * no dirty pages.  We can safely remove it from the
         * list of ordered extents
         */
        if (RB_EMPTY_ROOT(&tree->tree) &&
            !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
                list_del_init(&BTRFS_I(inode)->ordered_operations);
        }
        spin_unlock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);

        return 0;
}

/*
 * remove an ordered extent from the tree.  No references are dropped
 * but any waiters are woken.
 */
int btrfs_remove_ordered_extent(struct inode *inode,
                                struct btrfs_ordered_extent *entry)
{
        struct btrfs_ordered_inode_tree *tree;
        int ret;

        tree = &BTRFS_I(inode)->ordered_tree;
        mutex_lock(&tree->mutex);
        ret = __btrfs_remove_ordered_extent(inode, entry);
        mutex_unlock(&tree->mutex);
        wake_up(&entry->wait);

        return ret;
}

/*
 * wait for all the ordered extents in a root.  This is done when balancing
 * space between drives.
 */
int btrfs_wait_ordered_extents(struct btrfs_root *root,
                               int nocow_only, int delay_iput)
{
        struct list_head splice;
        struct list_head *cur;
        struct btrfs_ordered_extent *ordered;
        struct inode *inode;

        INIT_LIST_HEAD(&splice);

        spin_lock(&root->fs_info->ordered_extent_lock);
        list_splice_init(&root->fs_info->ordered_extents, &splice);
        while (!list_empty(&splice)) {
                cur = splice.next;
                ordered = list_entry(cur, struct btrfs_ordered_extent,
                                     root_extent_list);
                if (nocow_only &&
                    !test_bit(BTRFS_ORDERED_NOCOW, &ordered->flags) &&
                    !test_bit(BTRFS_ORDERED_PREALLOC, &ordered->flags)) {
                        list_move(&ordered->root_extent_list,
                                  &root->fs_info->ordered_extents);
                        cond_resched_lock(&root->fs_info->ordered_extent_lock);
                        continue;
                }

                list_del_init(&ordered->root_extent_list);
                atomic_inc(&ordered->refs);

                /*
                 * the inode may be getting freed (in sys_unlink path).
                 */
                inode = igrab(ordered->inode);

                spin_unlock(&root->fs_info->ordered_extent_lock);

                if (inode) {
                        btrfs_start_ordered_extent(inode, ordered, 1);
                        btrfs_put_ordered_extent(ordered);
                        if (delay_iput)
                                btrfs_add_delayed_iput(inode);
                        else
                                iput(inode);
                } else {
                        btrfs_put_ordered_extent(ordered);
                }

                spin_lock(&root->fs_info->ordered_extent_lock);
        }
        spin_unlock(&root->fs_info->ordered_extent_lock);
        return 0;
}

/*
 * this is used during transaction commit to write all the inodes
 * added to the ordered operation list.  These files must be fully on
 * disk before the transaction commits.
 *
 * we have two modes here, one is to just start the IO via filemap_flush
 * and the other is to wait for all the io.  When we wait, we have an
 * extra check to make sure the ordered operation list really is empty
 * before we return
 */
int btrfs_run_ordered_operations(struct btrfs_root *root, int wait)
{
        struct btrfs_inode *btrfs_inode;
        struct inode *inode;
        struct list_head splice;

        INIT_LIST_HEAD(&splice);

        mutex_lock(&root->fs_info->ordered_operations_mutex);
        spin_lock(&root->fs_info->ordered_extent_lock);
again:
        list_splice_init(&root->fs_info->ordered_operations, &splice);

        while (!list_empty(&splice)) {
                btrfs_inode = list_entry(splice.next, struct btrfs_inode,
                                   ordered_operations);

                inode = &btrfs_inode->vfs_inode;

                list_del_init(&btrfs_inode->ordered_operations);

                /*
                 * the inode may be getting freed (in sys_unlink path).
                 */
                inode = igrab(inode);

                if (!wait && inode) {
                        list_add_tail(&BTRFS_I(inode)->ordered_operations,
                              &root->fs_info->ordered_operations);
                }
                spin_unlock(&root->fs_info->ordered_extent_lock);

                if (inode) {
                        if (wait)
                                btrfs_wait_ordered_range(inode, 0, (u64)-1);
                        else
                                filemap_flush(inode->i_mapping);
                        btrfs_add_delayed_iput(inode);
                }

                cond_resched();
                spin_lock(&root->fs_info->ordered_extent_lock);
        }
        if (wait && !list_empty(&root->fs_info->ordered_operations))
                goto again;

        spin_unlock(&root->fs_info->ordered_extent_lock);
        mutex_unlock(&root->fs_info->ordered_operations_mutex);

        return 0;
}

/*
 * Used to start IO or wait for a given ordered extent to finish.
 *
 * If wait is one, this effectively waits on page writeback for all the pages
 * in the extent, and it waits on the io completion code to insert
 * metadata into the btree corresponding to the extent
 */
void btrfs_start_ordered_extent(struct inode *inode,
                                       struct btrfs_ordered_extent *entry,
                                       int wait)
{
        u64 start = entry->file_offset;
        u64 end = start + entry->len - 1;

        /*
         * pages in the range can be dirty, clean or writeback.  We
         * start IO on any dirty ones so the wait doesn't stall waiting
         * for pdflush to find them
         */
        filemap_fdatawrite_range(inode->i_mapping, start, end);
        if (wait) {
                wait_event(entry->wait, test_bit(BTRFS_ORDERED_COMPLETE,
                                                 &entry->flags));
        }
}

/*
 * Used to wait on ordered extents across a large range of bytes.
 */
int btrfs_wait_ordered_range(struct inode *inode, u64 start, u64 len)
{
        u64 end;
        u64 orig_end;
        u64 wait_end;
        struct btrfs_ordered_extent *ordered;
        int found;

        if (start + len < start) {
                orig_end = INT_LIMIT(loff_t);
        } else {
                orig_end = start + len - 1;
                if (orig_end > INT_LIMIT(loff_t))
                        orig_end = INT_LIMIT(loff_t);
        }
        wait_end = orig_end;
again:
        /* start IO across the range first to instantiate any delalloc
         * extents
         */
        filemap_fdatawrite_range(inode->i_mapping, start, orig_end);

        /* The compression code will leave pages locked but return from
         * writepage without setting the page writeback.  Starting again
         * with WB_SYNC_ALL will end up waiting for the IO to actually start.
         */
        filemap_fdatawrite_range(inode->i_mapping, start, orig_end);

        filemap_fdatawait_range(inode->i_mapping, start, orig_end);

        end = orig_end;
        found = 0;
        while (1) {
                ordered = btrfs_lookup_first_ordered_extent(inode, end);
                if (!ordered)
                        break;
                if (ordered->file_offset > orig_end) {
                        btrfs_put_ordered_extent(ordered);
                        break;
                }
                if (ordered->file_offset + ordered->len < start) {
                        btrfs_put_ordered_extent(ordered);
                        break;
                }
                found++;
                btrfs_start_ordered_extent(inode, ordered, 1);
                end = ordered->file_offset;
                btrfs_put_ordered_extent(ordered);
                if (end == 0 || end == start)
                        break;
                end--;
        }
        if (found || test_range_bit(&BTRFS_I(inode)->io_tree, start, orig_end,
                           EXTENT_DELALLOC, 0, NULL)) {
                schedule_timeout(1);
                goto again;
        }
        return 0;
}

/*
 * find an ordered extent corresponding to file_offset.  return NULL if
 * nothing is found, otherwise take a reference on the extent and return it
 */
struct btrfs_ordered_extent *btrfs_lookup_ordered_extent(struct inode *inode,
                                                         u64 file_offset)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry = NULL;

        tree = &BTRFS_I(inode)->ordered_tree;
        mutex_lock(&tree->mutex);
        node = tree_search(tree, file_offset);
        if (!node)
                goto out;

        entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
        if (!offset_in_entry(entry, file_offset))
                entry = NULL;
        if (entry)
                atomic_inc(&entry->refs);
out:
        mutex_unlock(&tree->mutex);
        return entry;
}

/*
 * lookup and return any extent before 'file_offset'.  NULL is returned
 * if none is found
 */
struct btrfs_ordered_extent *
btrfs_lookup_first_ordered_extent(struct inode *inode, u64 file_offset)
{
        struct btrfs_ordered_inode_tree *tree;
        struct rb_node *node;
        struct btrfs_ordered_extent *entry = NULL;

        tree = &BTRFS_I(inode)->ordered_tree;
        mutex_lock(&tree->mutex);
        node = tree_search(tree, file_offset);
        if (!node)
                goto out;

        entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
        atomic_inc(&entry->refs);
out:
        mutex_unlock(&tree->mutex);
        return entry;
}

/*
 * After an extent is done, call this to conditionally update the on disk
 * i_size.  i_size is updated to cover any fully written part of the file.
 */
int btrfs_ordered_update_i_size(struct inode *inode, u64 offset,
                                struct btrfs_ordered_extent *ordered)
{
        struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
        struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
        u64 disk_i_size;
        u64 new_i_size;
        u64 i_size_test;
        u64 i_size = i_size_read(inode);
        struct rb_node *node;
        struct rb_node *prev = NULL;
        struct btrfs_ordered_extent *test;
        int ret = 1;

        if (ordered)
                offset = entry_end(ordered);
        else
                offset = ALIGN(offset, BTRFS_I(inode)->root->sectorsize);

        mutex_lock(&tree->mutex);
        disk_i_size = BTRFS_I(inode)->disk_i_size;

        /* truncate file */
        if (disk_i_size > i_size) {
                BTRFS_I(inode)->disk_i_size = i_size;
                ret = 0;
                goto out;
        }

        /*
         * if the disk i_size is already at the inode->i_size, or
         * this ordered extent is inside the disk i_size, we're done
         */
        if (disk_i_size == i_size || offset <= disk_i_size) {
                goto out;
        }

        /*
         * we can't update the disk_isize if there are delalloc bytes
         * between disk_i_size and  this ordered extent
         */
        if (test_range_bit(io_tree, disk_i_size, offset - 1,
                           EXTENT_DELALLOC, 0, NULL)) {
                goto out;
        }
        /*
         * walk backward from this ordered extent to disk_i_size.
         * if we find an ordered extent then we can't update disk i_size
         * yet
         */
        if (ordered) {
                node = rb_prev(&ordered->rb_node);
        } else {
                prev = tree_search(tree, offset);
                /*
                 * we insert file extents without involving ordered struct,
                 * so there should be no ordered struct cover this offset
                 */
                if (prev) {
                        test = rb_entry(prev, struct btrfs_ordered_extent,
                                        rb_node);
                        BUG_ON(offset_in_entry(test, offset));
                }
                node = prev;
        }
        while (node) {
                test = rb_entry(node, struct btrfs_ordered_extent, rb_node);
                if (test->file_offset + test->len <= disk_i_size)
                        break;
                if (test->file_offset >= i_size)
                        break;
                if (test->file_offset >= disk_i_size)
                        goto out;
                node = rb_prev(node);
        }
        new_i_size = min_t(u64, offset, i_size);

        /*
         * at this point, we know we can safely update i_size to at least
         * the offset from this ordered extent.  But, we need to
         * walk forward and see if ios from higher up in the file have
         * finished.
         */
        if (ordered) {
                node = rb_next(&ordered->rb_node);
        } else {
                if (prev)
                        node = rb_next(prev);
                else
                        node = rb_first(&tree->tree);
        }
        i_size_test = 0;
        if (node) {
                /*
                 * do we have an area where IO might have finished
                 * between our ordered extent and the next one.
                 */
                test = rb_entry(node, struct btrfs_ordered_extent, rb_node);
                if (test->file_offset > offset)
                        i_size_test = test->file_offset;
        } else {
                i_size_test = i_size;
        }

        /*
         * i_size_test is the end of a region after this ordered
         * extent where there are no ordered extents.  As long as there
         * are no delalloc bytes in this area, it is safe to update
         * disk_i_size to the end of the region.
         */
        if (i_size_test > offset &&
            !test_range_bit(io_tree, offset, i_size_test - 1,
                            EXTENT_DELALLOC, 0, NULL)) {
                new_i_size = min_t(u64, i_size_test, i_size);
        }
        BTRFS_I(inode)->disk_i_size = new_i_size;
        ret = 0;
out:
        /*
         * we need to remove the ordered extent with the tree lock held
         * so that other people calling this function don't find our fully
         * processed ordered entry and skip updating the i_size
         */
        if (ordered)
                __btrfs_remove_ordered_extent(inode, ordered);
        mutex_unlock(&tree->mutex);
        if (ordered)
                wake_up(&ordered->wait);
        return ret;
}

/*
 * search the ordered extents for one corresponding to 'offset' and
 * try to find a checksum.  This is used because we allow pages to
 * be reclaimed before their checksum is actually put into the btree
 */
int btrfs_find_ordered_sum(struct inode *inode, u64 offset, u64 disk_bytenr,
                           u32 *sum)
{
        struct btrfs_ordered_sum *ordered_sum;
        struct btrfs_sector_sum *sector_sums;
        struct btrfs_ordered_extent *ordered;
        struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
        unsigned long num_sectors;
        unsigned long i;
        u32 sectorsize = BTRFS_I(inode)->root->sectorsize;
        int ret = 1;

        ordered = btrfs_lookup_ordered_extent(inode, offset);
        if (!ordered)
                return 1;

        mutex_lock(&tree->mutex);
        list_for_each_entry_reverse(ordered_sum, &ordered->list, list) {
                if (disk_bytenr >= ordered_sum->bytenr) {
                        num_sectors = ordered_sum->len / sectorsize;
                        sector_sums = ordered_sum->sums;
                        for (i = 0; i < num_sectors; i++) {
                                if (sector_sums[i].bytenr == disk_bytenr) {
                                        *sum = sector_sums[i].sum;
                                        ret = 0;
                                        goto out;
                                }
                        }
                }
        }
out:
        mutex_unlock(&tree->mutex);
        btrfs_put_ordered_extent(ordered);
        return ret;
}


/*
 * add a given inode to the list of inodes that must be fully on
 * disk before a transaction commit finishes.
 *
 * This basically gives us the ext3 style data=ordered mode, and it is mostly
 * used to make sure renamed files are fully on disk.
 *
 * It is a noop if the inode is already fully on disk.
 *
 * If trans is not null, we'll do a friendly check for a transaction that
 * is already flushing things and force the IO down ourselves.
 */
int btrfs_add_ordered_operation(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                struct inode *inode)
{
        u64 last_mod;

        last_mod = max(BTRFS_I(inode)->generation, BTRFS_I(inode)->last_trans);

        /*
         * if this file hasn't been changed since the last transaction
         * commit, we can safely return without doing anything
         */
        if (last_mod < root->fs_info->last_trans_committed)
                return 0;

        /*
         * the transaction is already committing.  Just start the IO and
         * don't bother with all of this list nonsense
         */
        if (trans && root->fs_info->running_transaction->blocked) {
                btrfs_wait_ordered_range(inode, 0, (u64)-1);
                return 0;
        }

        spin_lock(&root->fs_info->ordered_extent_lock);
        if (list_empty(&BTRFS_I(inode)->ordered_operations)) {
                list_add_tail(&BTRFS_I(inode)->ordered_operations,
                              &root->fs_info->ordered_operations);
        }
        spin_unlock(&root->fs_info->ordered_extent_lock);

        return 0;
}