md: allow a maximum extent to be set for resyncing

This allows userspace to control resync/reshape progress and synchronise it
with other activities, such as shared access in a SAN, or backing up critical
sections during a tricky reshape.

Writing a number of sectors (which must be a multiple of the chunk size if
such is meaningful) causes a resync to pause when it gets to that point.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index ba125277c6c4..d6f12882424d 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1657,6 +1657,9 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
                 return (max_sector - sector_nr) + sectors_skipped;
         }
 
+        if (max_sector > mddev->resync_max)
+                max_sector = mddev->resync_max; /* Don't do IO beyond here */
+
         /* make sure whole request will fit in a chunk - if chunks
          * are meaningful
          */