xfs: always succeed when deduping zero bytes

commit fba3e594ef0ad911fa8f559732d588172f212d71 upstream.

It turns out that btrfs and xfs had differing interpretations of what
to do when the dedupe length is zero.  Change xfs to follow btrfs'
semantics so that the userland interface is consistent.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 0edf835af32d..4d99100a4bbf 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1345,8 +1345,14 @@ xfs_reflink_remap_range(
                 goto out_unlock;
         }
 
-        if (len == 0)
+        /* Zero length dedupe exits immediately; reflink goes to EOF. */
+        if (len == 0) {
+                if (is_dedupe) {
+                        ret = 0;
+                        goto out_unlock;
+                }
                 len = isize - pos_in;
+        }
 
         /* Ensure offsets don't wrap and the input is inside i_size */
         if (pos_in + len < pos_in || pos_out + len < pos_out ||