[PATCH 11/22] block: Use bdrv_recurse_can_replace()

[Max Reitz <mreitz@redhat.com>]

Let check_to_replace_node() use the more specialized
bdrv_recurse_can_replace() instead of
bdrv_recurse_is_first_non_filter(), which is too restrictive.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index a2deca4ac9..02177bde9a 100644
--- a/block.c
+++ b/block.c
@@ -6244,6 +6244,17 @@ bool bdrv_recurse_can_replace(BlockDriverState *bs,
     return false;
 }
 
+/*
+ * Check whether the given @node_name can be replaced by a node that
+ * has the same data as @parent_bs.  If so, return @node_name's BDS;
+ * NULL otherwise.
+ *
+ * @node_name must be a (recursive) *child of @parent_bs (or this
+ * function will return NULL).
+ *
+ * The result (whether the node can be replaced or not) is only valid
+ * for as long as no graph changes occur.
+ */
 BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
                                         const char *node_name, Error **errp)
 {
@@ -6268,8 +6279,11 @@ BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
      * Another benefit is that this tests exclude backing files which are
      * blocked by the backing blockers.
      */
-    if (!bdrv_recurse_is_first_non_filter(parent_bs, to_replace_bs)) {
-        error_setg(errp, "Only top most non filter can be replaced");
+    if (!bdrv_recurse_can_replace(parent_bs, to_replace_bs)) {
+        error_setg(errp, "Cannot replace '%s' by a node mirrored from '%s', "
+                   "because it cannot be guaranteed that doing so would not "
+                   "lead to an abrupt change of visible data",
+                   node_name, parent_bs->node_name);
         to_replace_bs = NULL;
         goto out;
     }
-- 
2.21.0