block: Add BDS.never_freeze

The commit and the mirror block job must be able to drop their filter
node at any point.  However, this will not be possible if any of the
BdrvChild links to them is frozen.  Therefore, we need to prevent them
from ever becoming frozen.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20190703172813.6868-2-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/block.c b/block.c
index c139540f2b..6565192b91 100644
--- a/block.c
+++ b/block.c
@@ -4417,6 +4417,14 @@ int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
     }
 
     for (i = bs; i != base; i = backing_bs(i)) {
+        if (i->backing && backing_bs(i)->never_freeze) {
+            error_setg(errp, "Cannot freeze '%s' link to '%s'",
+                       i->backing->name, backing_bs(i)->node_name);
+            return -EPERM;
+        }
+    }
+
+    for (i = bs; i != base; i = backing_bs(i)) {
         if (i->backing) {
             i->backing->frozen = true;
         }