From 9bd910e2cbe413ab5927068bf189e929cb6790bc Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Fri, 10 Jun 2016 20:57:46 +0200 Subject: [PATCH] block: Allow replacement of a BDS by its overlay 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 Message-id: 20160610185750.30956-2-mreitz@redhat.com Reviewed-by: Kevin Wolf Reviewed-by: Fam Zheng Signed-off-by: Max Reitz --- block.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/block.c b/block.c index 8104225cd3..d090324c68 100644 --- a/block.c +++ b/block.c @@ -2226,9 +2226,23 @@ 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);