block: directly invoke .bdrv_* from emulation functions

The emulation functions which supply default BlockDriver .bdrv_*()
functions given another implemented .bdrv_*() function should not use
public bdrv_*() interfaces.  This patch ensures they invoke .bdrv_*()
directly to avoid adding an extra layer of coroutine request processing
and possibly entering an infinite loop.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -2739,9 +2739,9 @@ static BlockDriverAIOCB *bdrv_aio_rw_vector(BlockDriverState *bs,
 
     if (is_write) {
         qemu_iovec_to_buffer(acb->qiov, acb->bounce);
-        acb->ret = bdrv_write(bs, sector_num, acb->bounce, nb_sectors);
+        acb->ret = bs->drv->bdrv_write(bs, sector_num, acb->bounce, nb_sectors);
     } else {
-        acb->ret = bdrv_read(bs, sector_num, acb->bounce, nb_sectors);
+        acb->ret = bs->drv->bdrv_read(bs, sector_num, acb->bounce, nb_sectors);
     }
 
     qemu_bh_schedule(acb->bh);
@@ -2906,8 +2906,9 @@ static int bdrv_read_em(BlockDriverState *bs, int64_t sector_num,
     iov.iov_base = (void *)buf;
     iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE;
     qemu_iovec_init_external(&qiov, &iov, 1);
-    acb = bdrv_aio_readv(bs, sector_num, &qiov, nb_sectors,
-        bdrv_rw_em_cb, &async_ret);
+
+    acb = bs->drv->bdrv_aio_readv(bs, sector_num, &qiov, nb_sectors,
+                                  bdrv_rw_em_cb, &async_ret);
     if (acb == NULL) {
         async_ret = -1;
         goto fail;
@@ -2934,8 +2935,9 @@ static int bdrv_write_em(BlockDriverState *bs, int64_t sector_num,
     iov.iov_base = (void *)buf;
     iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE;
     qemu_iovec_init_external(&qiov, &iov, 1);
-    acb = bdrv_aio_writev(bs, sector_num, &qiov, nb_sectors,
-        bdrv_rw_em_cb, &async_ret);
+
+    acb = bs->drv->bdrv_aio_writev(bs, sector_num, &qiov, nb_sectors,
+                                   bdrv_rw_em_cb, &async_ret);
     if (acb == NULL) {
         async_ret = -1;
         goto fail;