@@ -3432,7 +3432,7 @@ void bdrv_close_all(void)
static bool should_update_child(BdrvChild *c, BlockDriverState *to)
{
- BdrvChild *to_c;
+ GList *queue = NULL, *pos;
if (c->role->stay_at_node) {
return false;
@@ -3468,13 +3468,35 @@ static bool should_update_child(BdrvChild *c, BlockDriverState *to)
* if A is a child of B, that means we cannot replace A by B there
* because that would create a loop. Silently detaching A from B
* is also not really an option. So overall just leaving A in
- * place there is the most sensible choice. */
- QLIST_FOREACH(to_c, &to->children, next) {
- if (to_c == c) {
- return false;
+ * place there is the most sensible choice.
+ *
+ * upd: If the child @c belongs to the @to's children, or children of it's
+ * children and so on - this would create a loop to. To prevent it let's do
+ * a BFS search on @to children subtree.
+ */
+
+ pos = queue = g_list_append(queue, to);
+ while (pos) {
+ BlockDriverState *v = pos->data;
+ BdrvChild *c2;
+
+ QLIST_FOREACH(c2, &v->children, next) {
+ if (c2 == c) {
+ g_list_free(queue);
+ return false;
+ }
+
+ if (g_list_find(queue, c2->bs)) {
+ continue;
+ }
+
+ queue = g_list_append(queue, c2->bs);
}
+
+ pos = pos->next;
}
+ g_list_free(queue);
return true;
}
As it already said in the comment, we don't want to create loops in parent->child relations. So, when we try to append @to to @c, we should check that @c is not in @to children subtree, and we should check it recursively, not only the first level. The patch provides BFS-based search, to check the relations. This is needed for further fleecing-hook filter usage: we need to append it to source, when the hook is already a parent of target, and source may be in a backing chain of target (fleecing-scheme). So, on appending, the hook should not became a child (direct or through children subtree) of the target. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> --- block.c | 32 +++++++++++++++++++++++++++----- 1 file changed, 27 insertions(+), 5 deletions(-)