[PATCH 06/20] block: assert that graph read and writes are performed correctly

[Emanuele Giuseppe Esposito]

Remove the old assert_bdrv_graph_writable, and replace it with
the new version using graph-lock API.
See the function documentation for more information.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block.c                                |  4 ++--
 block/graph-lock.c                     | 11 +++++++++++
 include/block/block_int-global-state.h | 17 -----------------
 include/block/graph-lock.h             | 15 +++++++++++++++
 4 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/block.c b/block.c
index afab74d4da..1c870d85e6 100644
--- a/block.c
+++ b/block.c
@@ -1414,7 +1414,7 @@ static void bdrv_child_cb_attach(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
 
-    assert_bdrv_graph_writable(bs);
+    assert_bdrv_graph_writable();
     QLIST_INSERT_HEAD(&bs->children, child, next);
 
     if (bs->drv->is_filter || (child->role & BDRV_CHILD_FILTERED)) {
@@ -1461,7 +1461,7 @@ static void bdrv_child_cb_detach(BdrvChild *child)
         bdrv_backing_detach(child);
     }
 
-    assert_bdrv_graph_writable(bs);
+    assert_bdrv_graph_writable();
     QLIST_REMOVE(child, next);
     if (child == bs->backing) {
         assert(child != bs->file);
diff --git a/block/graph-lock.c b/block/graph-lock.c
index c3c6eeedad..07476fd7c8 100644
--- a/block/graph-lock.c
+++ b/block/graph-lock.c
@@ -242,3 +242,14 @@ void coroutine_fn bdrv_graph_co_rdunlock(void)
         aio_wait_kick();
     }
 }
+
+void assert_bdrv_graph_readable(void)
+{
+    assert(qemu_in_main_thread() || reader_count());
+}
+
+void assert_bdrv_graph_writable(void)
+{
+    assert(qemu_in_main_thread());
+    assert(qatomic_read(&has_writer));
+}
diff --git a/include/block/block_int-global-state.h 
b/include/block/block_int-global-state.h
index b49f4eb35b..2f0993f6e9 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -310,21 +310,4 @@ void bdrv_remove_aio_context_notifier(BlockDriverState *bs,
  */
 void bdrv_drain_all_end_quiesce(BlockDriverState *bs);
 
-/**
- * Make sure that the function is running under both drain and BQL.
- * The latter protects from concurrent writings
- * from the GS API, while the former prevents concurrent reads
- * from I/O.
- */
-static inline void assert_bdrv_graph_writable(BlockDriverState *bs)
-{
-    /*
-     * TODO: this function is incomplete. Because the users of this
-     * assert lack the necessary drains, check only for BQL.
-     * Once the necessary drains are added,
-     * assert also for qatomic_read(&bs->quiesce_counter) > 0
-     */
-    assert(qemu_in_main_thread());
-}
-
 #endif /* BLOCK_INT_GLOBAL_STATE_H */
diff --git a/include/block/graph-lock.h b/include/block/graph-lock.h
index fc806aefa3..9430707dca 100644
--- a/include/block/graph-lock.h
+++ b/include/block/graph-lock.h
@@ -126,5 +126,20 @@ void coroutine_fn bdrv_graph_co_rdlock(void);
  */
 void coroutine_fn bdrv_graph_co_rdunlock(void);
 
+/*
+ * assert_bdrv_graph_readable:
+ * Make sure that the reader is either the main loop,
+ * or there is at least a reader helding the rdlock.
+ * In this way an incoming writer is aware of the read and waits.
+ */
+void assert_bdrv_graph_readable(void);
+
+/*
+ * assert_bdrv_graph_writable:
+ * Make sure that the writer is the main loop and has set @has_writer,
+ * so that incoming readers will pause.
+ */
+void assert_bdrv_graph_writable(void);
+
 #endif /* GRAPH_LOCK_H */
 
-- 
2.31.1