block: Add BdrvChildRole.stay_at_node

When the parents' child links are updated in bdrv_append() or
bdrv_replace_in_backing_chain(), this should affect all child links of
BlockBackends or other nodes, but not on child links held for other
purposes (like for setting permissions). This patch allows to control
the behaviour per BdrvChildRole.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Acked-by: Fam Zheng <famz@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/block.c b/block.c
index f72a67f230..9e538a5d41 100644
--- a/block.c
+++ b/block.c
@@ -2853,6 +2853,9 @@ static void change_parent_backing_link(BlockDriverState *from,
     BdrvChild *c, *next, *to_c;
 
     QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
+        if (c->role->stay_at_node) {
+            continue;
+        }
         if (c->role == &child_backing) {
             /* @from is generally not allowed to be a backing file, except for
              * when @to is the overlay. In that case, @from may not be replaced