From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43830) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bBRdA-0000GH-VH for qemu-devel@nongnu.org; Fri, 10 Jun 2016 14:58:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bBRd7-00017M-0n for qemu-devel@nongnu.org; Fri, 10 Jun 2016 14:58:08 -0400 From: Max Reitz Date: Fri, 10 Jun 2016 20:57:46 +0200 Message-Id: <20160610185750.30956-2-mreitz@redhat.com> In-Reply-To: <20160610185750.30956-1-mreitz@redhat.com> References: <20160610185750.30956-1-mreitz@redhat.com> Subject: [Qemu-devel] [PATCH v3 1/5] block: Allow replacement of a BDS by its overlay List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Max Reitz , Kevin Wolf , Fam Zheng change_parent_backing_link() asserts that the BDS to be replaced is not used as a backing file. However, we may want to replace a BDS by its overlay in which case that very link should not be redirected. For instance, when doing a sync=none drive-mirror operation, we may have the following BDS/BB forest before block job completion: target base <- source <- BlockBackend During job completion, we want to establish the source BDS as the target's backing node: target | v base <- source <- BlockBackend This makes the target a valid replacement for the source: target <- BlockBackend | v base <- source Without this modification to change_parent_backing_link() we have to inject the target into the graph before the source is its backing node, thus temporarily creating a wrong graph: target <- BlockBackend base <- source Signed-off-by: Max Reitz --- block.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/block.c b/block.c index f54bc25..dc76c159 100644 --- a/block.c +++ b/block.c @@ -2224,9 +2224,23 @@ void bdrv_close_all(void) static void change_parent_backing_link(BlockDriverState *from, BlockDriverState *to) { - BdrvChild *c, *next; + BdrvChild *c, *next, *to_c; QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) { + 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 + * by @to as @to's backing node. */ + QLIST_FOREACH(to_c, &to->children, next) { + if (to_c == c) { + break; + } + } + if (to_c) { + continue; + } + } + assert(c->role != &child_backing); bdrv_ref(to); bdrv_replace_child(c, to); -- 2.8.3