Btrfs: Fix file clone when source offset is not 0

Suppose:
- the source extent is: [0, 100]
- the src offset is 10
- the clone length is 90
- the dest offset is 0

This statement:

	new_key.offset = key.offset + destoff - off

will produce such an extent for the dest file:

	[ino, BTRFS_EXTENT_DATA_KEY, -10]

, which is obviously wrong.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index f87552a1d7ea..1b61dab64062 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1788,7 +1788,10 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 
                         memcpy(&new_key, &key, sizeof(new_key));
                         new_key.objectid = inode->i_ino;
-                        new_key.offset = key.offset + destoff - off;
+                        if (off <= key.offset)
+                                new_key.offset = key.offset + destoff - off;
+                        else
+                                new_key.offset = destoff;
 
                         trans = btrfs_start_transaction(root, 1);
                         if (IS_ERR(trans)) {