[RFC PATCH v2 11/25] include/block/blockjob.h: global state API

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

blockjob functions run always under the BQL lock.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/block/blockjob.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index d200f33c10..3bf384f8bf 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -77,6 +77,27 @@ typedef struct BlockJob {
     GSList *nodes;
 } BlockJob;
 
+/*
+ * 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.
+ */
+
 /**
  * block_job_next:
  * @job: A block job, or %NULL.
@@ -158,6 +179,8 @@ BlockJobInfo *block_job_query(BlockJob *job, Error **errp);
  */
 void block_job_iostatus_reset(BlockJob *job);
 
+/* Common functions that are neither I/O nor Global State */
+
 /**
  * block_job_is_internal:
  * @job: The job to determine if it is user-visible or not.
-- 
2.27.0