md/raid10: Allow skipping recovery when clean arrays are assembled

When an array is assembled incrementally with mdadm -I -R
and the array switches to "active" mode, md starts a recovery.

If the array was clean, the "fullsync" flag will be 0. Skip
the full recovery in this case, as RAID1 does (the code was
actually copied from the sync_request() method of RAID1).

Signed-off-by: Martin Wilck <mwilck@arcor.de>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 77b562d18a90..2372926dc559 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2913,6 +2913,22 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
                 if (init_resync(conf))
                         return 0;
 
+        /*
+         * Allow skipping a full rebuild for incremental assembly
+         * of a clean array, like RAID1 does.
+         */
+        if (mddev->bitmap == NULL &&
+            mddev->recovery_cp == MaxSector &&
+            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
+            conf->fullsync == 0) {
+                *skipped = 1;
+                max_sector = mddev->dev_sectors;
+                if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
+                    test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
+                        max_sector = mddev->resync_max_sectors;
+                return max_sector - sector_nr;
+        }
+
  skipped:
         max_sector = mddev->dev_sectors;
         if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||