block: Switch bdrv_io_limits_intercept() to byte granularity

Request sizes used to be rounded down to the next sector boundary,
allowing to bypass the I/O limit. Now all requests are accounted for
with their exact byte size.
Reported-by: NWenchao Xia <xiawenc@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>

block.c

@@ -192,7 +192,7 @@ void bdrv_io_limits_enable(BlockDriverState *bs)
  * @is_write:   is the IO a write
  */
 static void bdrv_io_limits_intercept(BlockDriverState *bs,
-                                     int nb_sectors,
+                                     unsigned int bytes,
                                      bool is_write)
 {
     /* does this io must wait */
@@ -205,9 +205,8 @@ static void bdrv_io_limits_intercept(BlockDriverState *bs,
     }
 
     /* the IO will be executed, do the accounting */
-    throttle_account(&bs->throttle_state,
-                     is_write,
-                     nb_sectors * BDRV_SECTOR_SIZE);
+    throttle_account(&bs->throttle_state, is_write, bytes);
+
 
     /* if the next request must wait -> do nothing */
     if (throttle_schedule_timer(&bs->throttle_state, is_write)) {
@@ -2968,8 +2967,7 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
 
     /* throttling disk I/O */
     if (bs->io_limits_enabled) {
-        /* TODO Switch to byte granularity */
-        bdrv_io_limits_intercept(bs, bytes >> BDRV_SECTOR_BITS, false);
+        bdrv_io_limits_intercept(bs, bytes, false);
     }
 
     /* Align read if necessary by padding qiov */
@@ -3193,8 +3191,7 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
 
     /* throttling disk I/O */
     if (bs->io_limits_enabled) {
-        /* TODO Switch to byte granularity */
-        bdrv_io_limits_intercept(bs, bytes >> BDRV_SECTOR_BITS, true);
+        bdrv_io_limits_intercept(bs, bytes, true);
     }
 
     /*