block: drain from main loop thread in bdrv_co_yield_to_drain()

For simplicity, always run BlockDevOps .drained_begin/end/poll()
callbacks in the main loop thread. This makes it easier to implement the
callbacks and avoids extra locks.

Move the function pointer declarations from the I/O Code section to the
Global State section for BlockDevOps, BdrvChildClass, and BlockDriver.

Narrow IO_OR_GS_CODE() to GLOBAL_STATE_CODE() where appropriate.

The test-bdrv-drain test case calls bdrv_drain() from an IOThread. This
is now only allowed from coroutine context, so update the test case to
run in a coroutine.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230516190238.8401-11-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 13 insertions, 12 deletions

diff --git a/include/sysemu/block-backend-common.h b/include/sysemu/block-backend-common.h
index 2391679c56..780cea7305 100644
--- a/include/sysemu/block-backend-common.h
+++ b/include/sysemu/block-backend-common.h
@@ -60,6 +60,19 @@ typedef struct BlockDevOps {
     bool (*is_medium_locked)(void *opaque);
 
     /*
+     * Runs when the backend receives a drain request.
+     */
+    void (*drained_begin)(void *opaque);
+    /*
+     * Runs when the backend's last drain request ends.
+     */
+    void (*drained_end)(void *opaque);
+    /*
+     * Is the device still busy?
+     */
+    bool (*drained_poll)(void *opaque);
+
+    /*
      * I/O API functions. These functions are thread-safe.
      *
      * See include/block/block-io.h for more information about
@@ -76,18 +89,6 @@ typedef struct BlockDevOps {
      * Runs when the size changed (e.g. monitor command block_resize)
      */
     void (*resize_cb)(void *opaque);
-    /*
-     * Runs when the backend receives a drain request.
-     */
-    void (*drained_begin)(void *opaque);
-    /*
-     * Runs when the backend's last drain request ends.
-     */
-    void (*drained_end)(void *opaque);
-    /*
-     * Is the device still busy?
-     */
-    bool (*drained_poll)(void *opaque);
 } BlockDevOps;
 
 /*