From nobody Sun Nov 9 14:49:23 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=virtuozzo.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1550949786687781.0425501760857; Sat, 23 Feb 2019 11:23:06 -0800 (PST) Received: from localhost ([127.0.0.1]:41746 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gxcsz-0006qb-0v for importer@patchew.org; Sat, 23 Feb 2019 14:22:57 -0500 Received: from eggs.gnu.org ([209.51.188.92]:54718) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gxcr1-0005re-8i for qemu-devel@nongnu.org; Sat, 23 Feb 2019 14:20:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gxcqx-00021v-Ob for qemu-devel@nongnu.org; Sat, 23 Feb 2019 14:20:53 -0500 Received: from relay.sw.ru ([185.231.240.75]:59146) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gxcqr-0001z5-N0; Sat, 23 Feb 2019 14:20:47 -0500 Received: from [10.28.8.145] (helo=kvm.sw.ru) by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1gxcqo-0004OX-0z; Sat, 23 Feb 2019 22:20:42 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-devel@nongnu.org, qemu-block@nongnu.org Date: Sat, 23 Feb 2019 22:20:39 +0300 Message-Id: <20190223192041.289782-2-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20190223192041.289782-1-vsementsov@virtuozzo.com> References: <20190223192041.289782-1-vsementsov@virtuozzo.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 185.231.240.75 Subject: [Qemu-devel] [PATCH v6 1/3] block: improve should_update_child X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, den@virtuozzo.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" 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 --- v6: rewrite using GHashTable and GQueue for efficient BFS. block.c | 43 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 37 insertions(+), 6 deletions(-) diff --git a/block.c b/block.c index 4ad0e90d7e..d7c2ff655c 100644 --- a/block.c +++ b/block.c @@ -3542,7 +3542,9 @@ void bdrv_close_all(void) =20 static bool should_update_child(BdrvChild *c, BlockDriverState *to) { - BdrvChild *to_c; + GQueue *queue; + GHashTable *found; + bool ret; =20 if (c->role->stay_at_node) { return false; @@ -3578,14 +3580,43 @@ static bool should_update_child(BdrvChild *c, Block= DriverState *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 =3D=3D 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. + */ + + ret =3D true; + found =3D g_hash_table_new(NULL, NULL); + g_hash_table_add(found, to); + queue =3D g_queue_new(); + g_queue_push_tail(queue, to); + + while (!g_queue_is_empty(queue)) { + BlockDriverState *v =3D g_queue_pop_head(queue); + BdrvChild *c2; + + QLIST_FOREACH(c2, &v->children, next) { + if (c2 =3D=3D c) { + ret =3D false; + break; + } + + if (g_hash_table_contains(found, c2->bs)) { + continue; + } + + g_queue_push_tail(queue, c2->bs); + g_hash_table_add(found, c2->bs); } } =20 - return true; + g_queue_free(queue); + g_hash_table_destroy(found); + + return ret; } =20 void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to, --=20 2.18.0