block: Don't call ROUND_UP with negative values

The behaviour of the ROUND_UP macro with negative numbers isn't obvious.
It happens to do the right thing in this please, but better avoid it.

Suggested-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

diff --git a/block.c b/block.c
index a027823ea4f684fd1dca31a67a53128517a55b9d..b0c5025977f49ce1d8a71c6d66ef52f4c84ed96a 100644 (file)
--- a/block.c
+++ b/block.c
@@ -2915,8 +2915,8 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
         }
 
         total_sectors = DIV_ROUND_UP(len, BDRV_SECTOR_SIZE);
-        max_nb_sectors = MAX(0, ROUND_UP(total_sectors - sector_num,
-                                         align >> BDRV_SECTOR_BITS));
+        max_nb_sectors = ROUND_UP(MAX(0, total_sectors - sector_num),
+                                  align >> BDRV_SECTOR_BITS);
         if (max_nb_sectors > 0) {
             ret = drv->bdrv_co_readv(bs, sector_num,
                                      MIN(nb_sectors, max_nb_sectors), qiov);