Btrfs: fix defragmentation regression

There's an off-by-one bug:

  # create a file with lots of 4K file extents
  # btrfs fi defrag /mnt/file
  # sync
  # filefrag -v /mnt/file
  Filesystem type is: 9123683e
  File size of /mnt/file is 1228800 (300 blocks, blocksize 4096)
   ext logical physical expected length flags
     0       0     3372              64
     1      64     3136     3435      1
     2      65     3436     3136     64
     3     129     3201     3499      1
     4     130     3500     3201     64
     5     194     3266     3563      1
     6     195     3564     3266     64
     7     259     3331     3627      1
     8     260     3628     3331     40 eof

After this patch:

  ...
  # filefrag -v /mnt/file
  Filesystem type is: 9123683e
  File size of /mnt/file is 1228800 (300 blocks, blocksize 4096)
   ext logical physical expected length flags
     0       0     3372             300 eof
  /mnt/file: 1 extent found

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
(cherry picked from commit cbcc83265d929ac71553c1b5dafdb830171af947)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 01f0cba1cf96aab2e035608e38c12eac69543971..9c21833ea2aeeb6cc6faa46134040a6bb9625de4 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1105,7 +1105,6 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
 
                defrag_count += ret;
                balance_dirty_pages_ratelimited_nr(inode->i_mapping, ret);
-               i += ret;
 
                if (newer_than) {
                        if (newer_off == (u64)-1)
@@ -1125,7 +1124,10 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
                                break;
                        }
                } else {
-                       i++;
+                       if (ret > 0)
+                               i += ret;
+                       else
+                               i++;
                }
        }