block: Add blk_remove_bs()

This function removes the BlockDriverState associated with the given
BlockBackend from that BB and sets the BDS pointer in the BB to NULL.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -333,6 +333,18 @@ void blk_hide_on_behalf_of_hmp_drive_del(BlockBackend *blk)
     }
 }
 
+/*
+ * Disassociates the currently associated BlockDriverState from @blk.
+ */
+void blk_remove_bs(BlockBackend *blk)
+{
+    blk_update_root_state(blk);
+
+    blk->bs->blk = NULL;
+    bdrv_unref(blk->bs);
+    blk->bs = NULL;
+}
+
 /*
  * Associates a new BlockDriverState with @blk.
  */

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_remove_bs(BlockBackend *blk);
 void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs);
 
 void blk_hide_on_behalf_of_hmp_drive_del(BlockBackend *blk);