From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:42738) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gdDv3-0002hB-Fg for qemu-devel@nongnu.org; Sat, 29 Dec 2018 07:40:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gdDcE-0007ym-8i for qemu-devel@nongnu.org; Sat, 29 Dec 2018 07:21:26 -0500 From: Vladimir Sementsov-Ogievskiy Date: Sat, 29 Dec 2018 15:20:19 +0300 Message-Id: <20181229122027.42245-4-vsementsov@virtuozzo.com> In-Reply-To: <20181229122027.42245-1-vsementsov@virtuozzo.com> References: <20181229122027.42245-1-vsementsov@virtuozzo.com> Subject: [Qemu-devel] [PATCH v5 03/11] block: improve should_update_child List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: fam@euphon.net, stefanha@redhat.com, jcody@redhat.com, mreitz@redhat.com, kwolf@redhat.com, vsementsov@virtuozzo.com, den@openvz.org, eblake@redhat.com, jsnow@redhat.com 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 --- block.c | 33 ++++++++++++++++++++++++++++----- 1 file changed, 28 insertions(+), 5 deletions(-) diff --git a/block.c b/block.c index 4f5ff2cc12..8f04f293da 100644 --- a/block.c +++ b/block.c @@ -3536,7 +3536,7 @@ 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; @@ -3572,13 +3572,36 @@ 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. + * + * We would also create a loop in any cases where @c is only + * indirectly referenced by @to. Prevent this by returning false + * if @c is found (by breadth-first search) anywhere in the whole + * subtree of @to. + */ + + 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; } -- 2.18.0