Putting an active block node on top of an inactive one is strictly
speaking an invalid configuration and the next patch will turn it into a
hard error.
However, taking a snapshot while disk images are inactive after
completing migration has an important use case: After migrating to a
file, taking an external snapshot is what is needed to take a full VM
snapshot.
In order for this to keep working after the later patches, change
creating a snapshot such that it automatically inactivates an overlay
that is added on top of an already inactive node.
Signed-off-by: Kevin Wolf <kw...@redhat.com>
Acked-by: Fabiano Rosas <faro...@suse.de>
Reviewed-by: Eric Blake <ebl...@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
Message-ID: <20250204211407.381505-4-kw...@redhat.com>
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
blockdev.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/blockdev.c b/blockdev.c
index 218024497b..eb2517f1dd 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1497,6 +1497,22 @@ static void external_snapshot_action(TransactionAction
*action,
return;
}
+ /*
+ * Older QEMU versions have allowed adding an active parent node to an
+ * inactive child node. This is unsafe in the general case, but there is an
+ * important use case, which is taking a VM snapshot with migration to file
+ * and then adding an external snapshot while the VM is still stopped and
+ * images are inactive. Requiring the user to explicitly create the overlay
+ * as inactive would break compatibility, so just do it automatically here
+ * to keep this working.
+ */
+ if (bdrv_is_inactive(state->old_bs) && !bdrv_is_inactive(state->new_bs)) {
+ ret = bdrv_inactivate(state->new_bs, errp);
+ if (ret < 0) {
+ return;
+ }
+ }
+
ret = bdrv_append(state->new_bs, state->old_bs, errp);
if (ret < 0) {
return;
--
2.48.1
