block: Add list of children to BlockDriverState

This allows iterating over all children of a given BDS, not only
including bs->file and bs->backing_hd, but also driver-specific
ones like VMDK extents or Quorum children.

For bdrv_swap(), the list of children of the swapped BDS stays at that
BDS (because that's where the pointers stay as well). The list head
moves and pointers to it must be fixed up therefore.

The list of children in the parent of the swapped BDS is not affected by
the swap. The contents of the BDS objects is swapped, so the existing
pointer in the parent automatically points to the newly swapped in BDS.

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, 8 insertions, 0 deletions

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 662dd56..4ae5860 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -337,6 +337,12 @@ struct BdrvChildRole {
 extern const BdrvChildRole child_file;
 extern const BdrvChildRole child_format;
 
+typedef struct BdrvChild {
+    BlockDriverState *bs;
+    const BdrvChildRole *role;
+    QLIST_ENTRY(BdrvChild) next;
+} BdrvChild;
+
 /*
  * Note: the function bdrv_append() copies and swaps contents of
  * BlockDriverStates, so if you add new fields to this struct, please
@@ -431,6 +437,8 @@ struct BlockDriverState {
     /* long-running background operation */
     BlockJob *job;
 
+    QLIST_HEAD(, BdrvChild) children;
+
     QDict *options;
     BlockdevDetectZeroesOptions detect_zeroes;