[PULL 10/19] block: reverse order for reopen commits

[John Snow <jsnow@redhat.com>]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

It's needed to fix reopening qcow2 with bitmaps to RW. Currently it
can't work, as qcow2 needs write access to file child, to mark bitmaps
in-image with IN_USE flag. But usually children goes after parents in
reopen queue and file child is still RO on qcow2 reopen commit. Reverse
reopen order to fix it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Acked-by: Max Reitz <mreitz@redhat.com>
Acked-by: John Snow <jsnow@redhat.com>
Message-id: 20190927122355.7344-3-vsementsov@virtuozzo.com
Signed-off-by: John Snow <jsnow@redhat.com>
---
 block.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index aaf5d796284..c548885608d 100644
--- a/block.c
+++ b/block.c
@@ -3486,10 +3486,16 @@ int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp)
         bs_entry->perms_checked = true;
     }
 
-    /* If we reach this point, we have success and just need to apply the
-     * changes
+    /*
+     * If we reach this point, we have success and just need to apply the
+     * changes.
+     *
+     * Reverse order is used to comfort qcow2 driver: on commit it need to write
+     * IN_USE flag to the image, to mark bitmaps in the image as invalid. But
+     * children are usually goes after parents in reopen-queue, so go from last
+     * to first element.
      */
-    QTAILQ_FOREACH(bs_entry, bs_queue, entry) {
+    QTAILQ_FOREACH_REVERSE(bs_entry, bs_queue, entry) {
         bdrv_reopen_commit(&bs_entry->state);
     }
 
-- 
2.21.0