block: Introduce .bdrv_co_ioctl() driver callback

This allows drivers to implement ioctls in a coroutine-based way.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

block/io.c

@@ -2502,17 +2502,21 @@ int bdrv_co_ioctl(BlockDriverState *bs, int req, void *buf)
     BlockAIOCB *acb;
 
     tracked_request_begin(&tracked_req, bs, 0, 0, BDRV_TRACKED_IOCTL);
-    if (!drv || !drv->bdrv_aio_ioctl) {
+    if (!drv || (!drv->bdrv_aio_ioctl && !drv->bdrv_co_ioctl)) {
         co.ret = -ENOTSUP;
         goto out;
     }
 
-    acb = drv->bdrv_aio_ioctl(bs, req, buf, bdrv_co_io_em_complete, &co);
-    if (!acb) {
-        co.ret = -ENOTSUP;
-        goto out;
+    if (drv->bdrv_co_ioctl) {
+        co.ret = drv->bdrv_co_ioctl(bs, req, buf);
+    } else {
+        acb = drv->bdrv_aio_ioctl(bs, req, buf, bdrv_co_io_em_complete, &co);
+        if (!acb) {
+            co.ret = -ENOTSUP;
+            goto out;
+        }
+        qemu_coroutine_yield();
     }
-    qemu_coroutine_yield();
 out:
     tracked_request_end(&tracked_req);
     return co.ret;

include/block/block_int.h

@@ -244,6 +244,8 @@ struct BlockDriver {
     BlockAIOCB *(*bdrv_aio_ioctl)(BlockDriverState *bs,
         unsigned long int req, void *buf,
         BlockCompletionFunc *cb, void *opaque);
+    int coroutine_fn (*bdrv_co_ioctl)(BlockDriverState *bs,
+                                      unsigned long int req, void *buf);
 
     /* List of options for creating images, terminated by name == NULL */
     QemuOptsList *create_opts;