[Qemu-devel] [PATCH 1/1] block: fix alignment calculations in bdrv_co_do_zero_pwritev

[Qemu-devel] [PATCH 1/1] block: fix alignment calculations in bdrv_co_do_zero_pwritev

[Denis V. Lunev]

tail_padding_bytes is calculated wrong. F.e. for
    offset = 0
    bytes = 2048
    align = 512
we will have tail_padding_bytes = 512 which is definitely wrong. The patch
fixes that arithmetics.

Fortunately this problem is harmless, we will have 1 extra allocation and
free thus there is no need to put this into stable. The problem is here
from the very beginning.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Fam Zheng <famz@redhat.com>
---
 block/io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/io.c b/block/io.c
index a7142e0..1e1523b 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1452,7 +1452,7 @@ static int coroutine_fn bdrv_co_do_zero_pwritev(BdrvChild *child,
     int ret = 0;
 
     head_padding_bytes = offset & (align - 1);
-    tail_padding_bytes = align - ((offset + bytes) & (align - 1));
+    tail_padding_bytes = (align - (offset + bytes)) & (align - 1);
 
 
     assert(flags & BDRV_REQ_ZERO_WRITE);
-- 
2.7.4

Re: [Qemu-devel] [PATCH 1/1] block: fix alignment calculations in bdrv_co_do_zero_pwritev

[Eric Blake]

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On 04/26/2017 03:40 AM, Denis V. Lunev wrote:
> tail_padding_bytes is calculated wrong. F.e. for
>     offset = 0
>     bytes = 2048
>     align = 512
> we will have tail_padding_bytes = 512 which is definitely wrong. The patch
> fixes that arithmetics.
> 
> Fortunately this problem is harmless, we will have 1 extra allocation and
> free thus there is no need to put this into stable. The problem is here
> from the very beginning.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Fam Zheng <famz@redhat.com>
> ---
>  block/io.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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Re: [Qemu-devel] [Qemu-block] [PATCH 1/1] block: fix alignment calculations in bdrv_co_do_zero_pwritev

[Kevin Wolf]

Am 26.04.2017 um 10:40 hat Denis V. Lunev geschrieben:
> tail_padding_bytes is calculated wrong. F.e. for
>     offset = 0
>     bytes = 2048
>     align = 512
> we will have tail_padding_bytes = 512 which is definitely wrong. The patch
> fixes that arithmetics.
> 
> Fortunately this problem is harmless, we will have 1 extra allocation and
> free thus there is no need to put this into stable. The problem is here
> from the very beginning.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Fam Zheng <famz@redhat.com>

Thanks, applied to block-next.

Kevin