[PATCH] md: Allow re-add to work on array without bitmaps

When an array has a bitmap, a device can be removed and re-added and only
blocks changes since the removal (as recorded in the bitmap) will be resynced.

It should be possible to do a similar thing to arrays without bitmaps.  i.e.
if a device is removed and re-added and *no* changes have been made in the
interim, then the add should not require a resync.

This patch allows that option.  This means that when assembling an array one
device at a time (e.g.  during device discovery) the array can be enabled
read-only as soon as enough devices are available, but extra devices can still
be added without causing a resync.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index b3cfae41f76..cead918578a 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1625,6 +1625,12 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
         /* before building a request, check if we can skip these blocks..
          * This call the bitmap_start_sync doesn't actually record anything
          */
+        if (mddev->bitmap == NULL &&
+            mddev->recovery_cp == MaxSector &&
+            conf->fullsync == 0) {
+                *skipped = 1;
+                return max_sector - sector_nr;
+        }
         if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
             !conf->fullsync && !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {
                 /* We can skip this block, and probably several more */