netdev - Re: Misalignment, MIPS, and ip

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Message-ID: <CAHmME9qGoPGEFyqe0jBaZD5R51wHTEgAYb9edj+nu9nNPWSYCA@mail.gmail.com>
Date:   Thu, 8 Dec 2016 23:20:04 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     David Miller <davem@...emloft.net>
Cc:     Dave Taht <dave.taht@...il.com>, Netdev <netdev@...r.kernel.org>,
        linux-mips@...ux-mips.org, LKML <linux-kernel@...r.kernel.org>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>
Subject: Re: Misalignment, MIPS, and ip_hdr(skb)->version

Hi David,

On Thu, Dec 8, 2016 at 1:37 AM, David Miller <davem@...emloft.net> wrote:
> You really have to land the IP header on a proper 4 byte boundary.
>
> I would suggest pushing 3 dummy garbage bytes of padding at the front
> or the end of your header.

Are you sure 3 bytes to get 4 byte alignment is really the best? I was
thinking that adding 1 byte to get 2 byte alignment might be better,
since it would then ensure that the subsequent TCP header winds up
being 4 byte aligned. Or is this in fact not the desired trade off,
and so I should stick with the 3 bytes you suggested?

Jason