From: Darrick J. Wong djwong@kernel.org
Way back when we first implemented FICLONE for XFS, life was simple -- either the the entire remapping completed, or something happened and we had to return an errno explaining what happened. Neither of those ioctls support returning partial results, so it's all or nothing.
Then things got complicated when copy_file_range came along, because it actually can return the number of bytes copied, so commit 3f68c1f562f1e4 tried to make it so that we could return a partial result if the REMAP_FILE_CAN_SHORTEN flag is set. This is also how FIDEDUPERANGE can indicate that the kernel performed a partial deduplication.
Unfortunately, the logic is wrong if an error stops the remapping and CAN_SHORTEN is not set. Because those callers cannot return partial results, it is an error for ->remap_file_range to return a positive quantity that is less than the @len passed in. Implementations really should be returning a negative errno in this case, because that's what btrfs (which introduced FICLONE{,RANGE}) did.
Therefore, ->remap_range implementations cannot silently drop an errno that they might have when the number of bytes remapped is less than the number of bytes requested and CAN_SHORTEN is not set.
Found by running generic/562 on a 64k fsblock filesystem and wondering why it reported corrupt files.
Cc: stable@vger.kernel.org # v4.20 Fixes: 3fc9f5e409319e ("xfs: remove xfs_reflink_remap_range") Really-Fixes: 3f68c1f562f1e4 ("xfs: support returning partial reflink results") Signed-off-by: Darrick J. Wong djwong@kernel.org --- fs/xfs/xfs_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index b19916b11fd563..aba54e3c583661 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -1228,6 +1228,14 @@ xfs_file_remap_range( xfs_iunlock2_remapping(src, dest); if (ret) trace_xfs_reflink_remap_range_error(dest, ret, _RET_IP_); + /* + * If the caller did not set CAN_SHORTEN, then it is not prepared to + * handle partial results -- either the whole remap succeeds, or we + * must say why it did not. In this case, any error should be returned + * to the caller. + */ + if (ret && remapped < len && !(remap_flags & REMAP_FILE_CAN_SHORTEN)) + return ret; return remapped > 0 ? remapped : ret; }