From: Eric Blake <eblake@redhat.com>
Date: Thu, 23 Jun 2016 22:37:07 +0000 (-0600)
Subject: block: Fix harmless off-by-one in bdrv_aligned_preadv()
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=82524274eada16bfa2a263cbdbcae0fe948ed040;p=qemu.git

block: Fix harmless off-by-one in bdrv_aligned_preadv()

If the amount of data to read ends exactly on the total size
of the bs, then we were wasting time creating a local qiov
to read the data in preparation for what would normally be
appending zeroes beyond the end, even though this corner case
has nothing further to do.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---

diff --git a/block/io.c b/block/io.c
index 994d3fafbf..82c9ff0a04 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1036,7 +1036,7 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
     }
 
     max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align);
-    if (bytes < max_bytes) {
+    if (bytes <= max_bytes) {
         ret = bdrv_driver_preadv(bs, offset, bytes, qiov, 0);
     } else if (max_bytes > 0) {
         QEMUIOVector local_qiov;