block: Add blk_next_root_bs()

This function iterates over all BDSs attached to a BB. We are going to
need it when rewriting bdrv_next() so it no longer uses bdrv_states.

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

1 files changed, 24 insertions, 0 deletions

diff --git a/block/block-backend.c b/block/block-backend.c
index b3c3d39db8..7818aa2634 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -250,6 +250,30 @@ BlockBackend *blk_next(BlockBackend *blk)
 }
 
 /*
+ * Iterates over all BlockDriverStates which are attached to a BlockBackend.
+ * This function is for use by bdrv_next().
+ *
+ * @bs must be NULL or a BDS that is attached to a BB.
+ */
+BlockDriverState *blk_next_root_bs(BlockDriverState *bs)
+{
+    BlockBackend *blk;
+
+    if (bs) {
+        assert(bs->blk);
+        blk = bs->blk;
+    } else {
+        blk = NULL;
+    }
+
+    do {
+        blk = blk_all_next(blk);
+    } while (blk && !blk->bs);
+
+    return blk ? blk->bs : NULL;
+}
+
+/*
  * Add a BlockBackend into the list of backends referenced by the monitor, with
  * the given @name acting as the handle for the monitor.
  * Strictly for use by blockdev.c.