block: Add blk_insert_bs()

This function associates the given BlockDriverState with the given
BlockBackend.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -333,6 +333,17 @@ void blk_hide_on_behalf_of_hmp_drive_del(BlockBackend *blk)
     }
 }
 
+/*
+ * Associates a new BlockDriverState with @blk.
+ */
+void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs)
+{
+    assert(!blk->bs && !bs->blk);
+    bdrv_ref(bs);
+    blk->bs = bs;
+    bs->blk = blk;
+}
+
 /*
  * Attach device model @dev to @blk.
  * Return 0 on success, -EBUSY when a device model is attached already.

include/sysemu/block-backend.h

@@ -72,6 +72,7 @@ BlockBackend *blk_by_name(const char *name);
 BlockBackend *blk_next(BlockBackend *blk);
 
 BlockDriverState *blk_bs(BlockBackend *blk);
+void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs);
 
 void blk_hide_on_behalf_of_hmp_drive_del(BlockBackend *blk);