+/*
+ * Global state (GS) API. These functions run under the BQL lock.
+ *
+ * If a function modifies the graph, it also uses drain and/or
+ * aio_context_acquire/release to be sure it has unique access.
+ * aio_context locking is needed together with BQL because of
+ * the thread-safe I/O API that concurrently runs and accesses
+ * the graph without the BQL.
+ *
+ * It is important to note that not all of these functions are
+ * necessarily limited to running under the BQL, but they would
+ * require additional auditing and may small thread-safety changes
+ * to move them into the I/O API. Often it's not worth doing that
+ * work since the APIs are only used with the BQL held at the
+ * moment, so they have been placed in the GS API (for now).
+ *
+ * All functions below must use this assertion:
+ * g_assert(qemu_in_main_thread());
+ * to catch when they are accidentally called without the BQL.
+ */
This is comment is duplicated in many places. I suggest explaining it in
one place and using references in the other files:
/*
* Global state (GS) API. These functions run under the BQL lock.
*
* See include/block/block.h for more information about the GS API.
*/