netdev - Re: [PATCH] openvswitch: Fix alignment of struct sw_flow

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Date:	Thu, 5 Sep 2013 21:25:20 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Jesse Gross <jesse@...ira.com>
Cc:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	Andy Zhou <azhou@...ira.com>,
	Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [PATCH] openvswitch: Fix alignment of struct sw_flow_key.

On Thu, Sep 5, 2013 at 9:17 PM, Jesse Gross <jesse@...ira.com> wrote:
> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
> @@ -1981,6 +1981,7 @@ nla_put_failure:
>   * Returns zero if successful or a negative error code. */
>  int ovs_flow_init(void)
>  {
> +       BUILD_BUG_ON(__alignof__(struct sw_flow_key) % __alignof__(long));

> -} __aligned(__alignof__(long));
> +} __aligned(BITS_PER_LONG/8); /* Ensure that we can do comparisons as longs. */

These don't match: the struct definition says aligned to 4 or 8 bytes, the check
checks for a multiple of the alignment of "long", which is 2, 4 or 8.

Anyway, BITS_PER_LONG/8 is always a multiple of __alignof__(long), so your
check will never fail.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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