block: reverse order for reopen commits

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>

diff --git a/block.c b/block.c
index 0347632c6cea7036a4240af4f578a78592085496..cf312258a9828806ab4dd7e39ee3343235b6c99a 100644 (file)
--- 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);
     }