[Qemu-devel] [PATCH 1/2] block: Don't allow snapshots if the overlay has parent nodes

[Alberto Garcia]

This addresses scenarios where the overlay node of the
'blockdev-snapshot' parameter is a child of an existing node,
such as this one:

  { 'execute': 'blockdev-add', 'arguments':
    { 'options': { 'driver': 'qcow2',
                   'node-name': 'new0',
                   'file': { 'driver': 'file',
                             'filename': 'new.qcow2',
                             'node-name': 'file0' } } } }

  { 'execute': 'blockdev-snapshot', 'arguments':
    { 'node': 'virtio0',
      'overlay': 'file0' } }

Signed-off-by: Alberto Garcia <be...@igalia.com>
---
 blockdev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/blockdev.c b/blockdev.c
index a567a05..fcddb07 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1667,6 +1667,11 @@ static void 
external_snapshot_prepare(BlkTransactionState *common,
 
     if (state->new_bs->backing != NULL) {
         error_setg(errp, "The snapshot already has a backing image");
+        return;
+    }
+
+    if (!QLIST_EMPTY(&state->new_bs->parents)) {
+        error_setg(errp, "The snapshot is already being used");
     }
 }
 
-- 
2.6.1