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[Qemu-devel] [PATCH v3 1/5] block: Allow replacement of a BDS by its ove
From: |
Max Reitz |
Subject: |
[Qemu-devel] [PATCH v3 1/5] block: Allow replacement of a BDS by its overlay |
Date: |
Fri, 10 Jun 2016 20:57:46 +0200 |
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 <address@hidden>
---
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