block: Introduce bdrv_co_writev_flags()

This function will allow drivers to implement BDRV_REQ_FUA natively
instead of sending a separate flush after the write.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>

block/io.c

@@ -1154,13 +1154,20 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
     } else if (flags & BDRV_REQ_ZERO_WRITE) {
         bdrv_debug_event(bs, BLKDBG_PWRITEV_ZERO);
         ret = bdrv_co_do_write_zeroes(bs, sector_num, nb_sectors, flags);
+    } else if (drv->bdrv_co_writev_flags) {
+        bdrv_debug_event(bs, BLKDBG_PWRITEV);
+        ret = drv->bdrv_co_writev_flags(bs, sector_num, nb_sectors, qiov,
+                                        flags);
     } else {
+        assert(drv->supported_write_flags == 0);
         bdrv_debug_event(bs, BLKDBG_PWRITEV);
         ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, qiov);
     }
     bdrv_debug_event(bs, BLKDBG_PWRITEV_DONE);
 
-    if (ret == 0 && (flags & BDRV_REQ_FUA)) {
+    if (ret == 0 && (flags & BDRV_REQ_FUA) &&
+        !(drv->supported_write_flags & BDRV_REQ_FUA))
+    {
         ret = bdrv_co_flush(bs);
     }
 

include/block/block_int.h

@@ -155,6 +155,11 @@ struct BlockDriver {
         int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
     int coroutine_fn (*bdrv_co_writev)(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
+    int coroutine_fn (*bdrv_co_writev_flags)(BlockDriverState *bs,
+        int64_t sector_num, int nb_sectors, QEMUIOVector *qiov, int flags);
+
+    int supported_write_flags;
+
     /*
      * Efficiently zero a region of the disk image.  Typically an image format
      * would use a compact metadata representation to implement this.  This