[Qemu-devel] [PATCH 5/9] block: Avoid BDS.blk in bdrv_next()

[Kevin Wolf <kwolf@redhat.com>]

We just want to know whether a BDS has at least one BB attached in order
to avoid enumerating it twice. This doesn't depend on the exact BB that
is attached and 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>
---
 block.c                        |  4 ++--
 block/block-backend.c          | 17 +++++++++++++++++
 include/sysemu/block-backend.h |  1 +
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 4cc117d..66f918e 100644
--- a/block.c
+++ b/block.c
@@ -2904,7 +2904,7 @@ BlockDriverState *bdrv_next_node(BlockDriverState *bs)
  * the monitor or attached to a BlockBackend */
 BlockDriverState *bdrv_next(BlockDriverState *bs)
 {
-    if (!bs || bs->blk) {
+    if (!bs || bdrv_has_blk(bs)) {
         bs = blk_next_root_bs(bs);
         if (bs) {
             return bs;
@@ -2915,7 +2915,7 @@ BlockDriverState *bdrv_next(BlockDriverState *bs)
      * handled by the above block already */
     do {
         bs = bdrv_next_monitor_owned(bs);
-    } while (bs && bs->blk);
+    } while (bs && bdrv_has_blk(bs));
     return bs;
 }
 
diff --git a/block/block-backend.c b/block/block-backend.c
index dfc11b5..fdd1727 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -434,6 +434,23 @@ 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 1ae1ac9..bd68a17 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);
-- 
1.8.3.1