From: Kevin Wolf <kwolf@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: shhuiw@163.com, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] cow: make padding in the header explicit
Date: Thu, 4 Sep 2014 11:26:41 +0200 [thread overview]
Message-ID: <20140904092641.GB3897@noname.str.redhat.com> (raw)
In-Reply-To: <1409821121-20645-1-git-send-email-stefanha@redhat.com>
Am 04.09.2014 um 10:58 hat Stefan Hajnoczi geschrieben:
> On-disk structures should be marked packed so the compiler does not
> insert padding for field alignment. Padding should be explicit so
> on-disk layout is obvious and we don't rely on the architecture-specific
> ABI for alignment rules.
>
> The pahole(1) diff shows that the padding is now explicit and offsets
> are unchanged:
>
> char backing_file[1024]; /* 8 1024 */
> /* --- cacheline 16 boundary (1024 bytes) was 8 bytes ago --- */
> int32_t mtime; /* 1032 4 */
> -
> - /* XXX 4 bytes hole, try to pack */
> -
> + uint32_t padding; /* 1036 4 */
> uint64_t size; /* 1040 8 */
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
next prev parent reply other threads:[~2014-09-04 9:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-04 8:58 [Qemu-devel] [PATCH] cow: make padding in the header explicit Stefan Hajnoczi
2014-09-04 9:26 ` Kevin Wolf [this message]
2014-09-04 9:47 ` Benoît Canet
2014-09-04 12:07 ` Eric Blake
2014-09-04 12:57 ` shhuiw
2014-09-04 13:51 ` Stefan Hajnoczi
2014-09-04 14:10 ` Kevin Wolf
2014-09-04 15:43 ` Stefan Hajnoczi
2014-09-05 9:13 ` Kevin Wolf
2014-09-05 11:01 ` Markus Armbruster
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