When the parents' child links are updated in bdrv_append() or
bdrv_replace_in_backing_chain(), this should affect all child links of
BlockBackends or other nodes, but not on child links held for other
purposes (like for setting permissions). This patch allows to control
the behaviour per BdrvChildRole.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c                   | 3 +++
 include/block/block_int.h | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/block.c b/block.c
index a8a2fa7..c7c0a8b 100644
--- a/block.c
+++ b/block.c
@@ -2832,6 +2832,9 @@ static void change_parent_backing_link(BlockDriverState *from,
     BdrvChild *c, *next, *to_c;
 
     QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
+        if (c->role->stay_at_node) {
+            continue;
+        }
         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
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 3177b9f..a0d9328 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -441,6 +441,10 @@ typedef struct BdrvAioNotifier {
 } BdrvAioNotifier;
 
 struct BdrvChildRole {
+    /* If true, bdrv_replace_in_backing_chain() doesn't change the node this
+     * BdrvChild points to. */
+    bool stay_at_node;
+
     void (*inherit_options)(int *child_flags, QDict *child_options,
                             int parent_flags, QDict *parent_options);
 
-- 
1.8.3.1

On 21.02.2017 15:58, Kevin Wolf wrote:
> When the parents' child links are updated in bdrv_append() or
> bdrv_replace_in_backing_chain(), this should affect all child links of
> BlockBackends or other nodes, but not on child links held for other
> purposes (like for setting permissions). This patch allows to control
> the behaviour per BdrvChildRole.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block.c                   | 3 +++
>  include/block/block_int.h | 4 ++++
>  2 files changed, 7 insertions(+)

Reviewed-by: Max Reitz <mreitz@redhat.com>