[RFC PATCH v2 08/25] block: introduce assert_bdrv_graph_writable

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

We want to be sure that the functions that write the child and
parent list of a bs are either under BQL or drain.
If this guarantee holds, then we can read the list also in the I/O APIs.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block.c                                | 5 +++++
 block/io.c                             | 5 +++++
 include/block/block_int-global-state.h | 8 +++++++-
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index b912f517a4..7d1eb847a4 100644
--- a/block.c
+++ b/block.c
@@ -2711,12 +2711,14 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
         if (child->klass->detach) {
             child->klass->detach(child);
         }
+        assert_bdrv_graph_writable(old_bs);
         QLIST_REMOVE(child, next_parent);
     }
 
     child->bs = new_bs;
 
     if (new_bs) {
+        assert_bdrv_graph_writable(new_bs);
         QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
 
         /*
@@ -2917,6 +2919,7 @@ static int bdrv_attach_child_noperm(BlockDriverState *parent_bs,
         return ret;
     }
 
+    assert_bdrv_graph_writable(parent_bs);
     QLIST_INSERT_HEAD(&parent_bs->children, *child, next);
     /*
      * child is removed in bdrv_attach_child_common_abort(), so don't care to
@@ -3117,6 +3120,7 @@ static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child,
 void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child)
 {
     g_assert(qemu_in_main_thread());
+    assert_bdrv_graph_writable(parent);
     if (child == NULL) {
         return;
     }
@@ -4878,6 +4882,7 @@ static void bdrv_remove_filter_or_cow_child_abort(void *opaque)
     BdrvRemoveFilterOrCowChild *s = opaque;
     BlockDriverState *parent_bs = s->child->opaque;
 
+    assert_bdrv_graph_writable(parent_bs);
     QLIST_INSERT_HEAD(&parent_bs->children, s->child, next);
     if (s->is_backing) {
         parent_bs->backing = s->child;
diff --git a/block/io.c b/block/io.c
index 21dcc5d962..d184183b07 100644
--- a/block/io.c
+++ b/block/io.c
@@ -739,6 +739,11 @@ void bdrv_drain_all(void)
     bdrv_drain_all_end();
 }
 
+void assert_bdrv_graph_writable(BlockDriverState *bs)
+{
+    g_assert(qatomic_read(&bs->quiesce_counter) > 0 || qemu_in_main_thread());
+}
+
 /**
  * Remove an active request from the tracked requests list
  *
diff --git a/include/block/block_int-global-state.h b/include/block/block_int-global-state.h
index aad549cb85..a53ab146fc 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -343,4 +343,10 @@ void bdrv_remove_aio_context_notifier(BlockDriverState *bs,
  */
 void bdrv_drain_all_end_quiesce(BlockDriverState *bs);
 
-#endif /* BLOCK_INT_GLOBAL_STATE*/
+/**
+ * Make sure that the function is either running under
+ * drain, or under BQL.
+ */
+void assert_bdrv_graph_writable(BlockDriverState *bs);
+
+#endif /* BLOCK_INT_GLOBAL_STATE */
-- 
2.27.0