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, 2 insertions, 0 deletions

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index b579cc628303..c77dca3221ed 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -219,6 +219,8 @@ struct mddev_s
         atomic_t                        recovery_active; /* blocks scheduled, but not written */
         wait_queue_head_t               recovery_wait;
         sector_t                        recovery_cp;
+        sector_t                        resync_max;     /* resync should pause
+                                                         * when it gets here */
 
         spinlock_t                      write_lock;
         wait_queue_head_t               sb_wait;        /* for waiting on superblock updates */