[PATCH 6/9] xfs: reflink can skip remap existing mappings

Darrick J. Wong
2020-06-25T01:18:25Z

From: Darrick J. Wong <darrick.wong@oracle.com>

If the source and destination map are identical, we can skip the remap
step to save some time.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/xfs/xfs_reflink.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 72de7179399d..f1156f121b7d 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1031,6 +1031,23 @@ xfs_reflink_remap_extent(

trace_xfs_reflink_remap_extent_dest(ip, &smap);

+ /*
+ * Two extents mapped to the same physical block must not have
+ * different states; that's filesystem corruption. Move on to the next
+ * extent if they're both holes or both the same physical extent.
+ */
+ if (dmap->br_startblock == smap.br_startblock) {
+ ASSERT(dmap->br_startblock == smap.br_startblock);
+ if (dmap->br_state != smap.br_state)
+ error = -EFSCORRUPTED;
+ goto out_cancel;
+ }
+
+ /* If both extents are unwritten, leave them alone. */
+ if (dmap->br_state == XFS_EXT_UNWRITTEN &&
+ smap.br_state == XFS_EXT_UNWRITTEN)
+ goto out_cancel;
+
/* No reflinking if the AG of the dest mapping is low on space. */
if (dmap_written) {
error = xfs_reflink_ag_has_free_space(mp,