block: Add bdrv_has_blk()

In many cases we just want to know whether a BDS has at least one BB
attached, without needing to know the exact BB that is attached. In
contrast to bs->blk, this is still a valid question when more than one
BB can be attached, so just answer it by checking the parents list.

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

2 files changed, 18 insertions, 0 deletions

diff --git a/block/block-backend.c b/block/block-backend.c
index 8d6fc77b26..9dcac9792f 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -395,6 +395,23 @@ BlockDriverState *blk_bs(BlockBackend *blk)
 }
 
 /*
+ * Returns true if @bs has an associated BlockBackend.
+ */
+bool bdrv_has_blk(BlockDriverState *bs)
+{
+    BdrvChild *child;
+    QLIST_FOREACH(child, &bs->parents, next_parent) {
+        if (child->role == &child_root) {
+            assert(bs->blk);
+            return true;
+        }
+    }
+
+    assert(!bs->blk);
+    return false;
+}
+
+/*
  * Return @blk's DriveInfo if any, else null.
  */
 DriveInfo *blk_legacy_dinfo(BlockBackend *blk)
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 79f39b889e..44a222d884 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -99,6 +99,7 @@ BlockBackend *blk_by_public(BlockBackendPublic *public);
 BlockDriverState *blk_bs(BlockBackend *blk);
 void blk_remove_bs(BlockBackend *blk);
 void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs);
+bool bdrv_has_blk(BlockDriverState *bs);
 
 void blk_set_allow_write_beyond_eof(BlockBackend *blk, bool allow);
 void blk_iostatus_enable(BlockBackend *blk);