block: improve should_update_child
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: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: NKevin Wolf <kwolf@redhat.com>
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