block: Add BlockDriverState.inherits_from

Currently, the block layer assumes that any block node can have only one
parent, and if it has a parent, that it inherits some options/flags from
this parent.

This is not true any more: With references used in block device
creation, a single node can be used by multiple parents, or it can be
created separately and not inherit flags from any parent.

To handle reopens correctly, a node must know from which parent it
inherited options. This patch adds the information to BlockDriverState.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 4ae5860..2732ccd 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -437,6 +437,10 @@ struct BlockDriverState {
     /* long-running background operation */
     BlockJob *job;
 
+    /* The node that this node inherited default options from (and a reopen on
+     * which can affect this node by changing these defaults). This is always a
+     * parent node of this node. */
+    BlockDriverState *inherits_from;
     QLIST_HEAD(, BdrvChild) children;
 
     QDict *options;