From: Greg KH <gregkh@linuxfoundation.org>
To: "Dan Lüdtke" <mail@danrl.com>
Cc: linux-mips@linux-mips.org, Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
WireGuard mailing list <wireguard@lists.zx2c4.com>
Subject: Re: Misalignment, MIPS, and ip_hdr(skb)->version
Date: Sun, 11 Dec 2016 08:15:01 +0100 [thread overview]
Message-ID: <20161211071501.GA32621@kroah.com> (raw)
In-Reply-To: <CE942916-BF45-44CC-A5F5-3838CF9C93BC@danrl.com>
On Sat, Dec 10, 2016 at 11:18:14PM +0100, Dan Lüdtke wrote:
>
> > On 8 Dec 2016, at 05:34, Daniel Kahn Gillmor <dkg@fifthhorseman.net> wrote:
> >
> > On Wed 2016-12-07 19:30:34 -0500, Hannes Frederic Sowa wrote:
> >> Your custom protocol should be designed in a way you get an aligned ip
> >> header. Most protocols of the IETF follow this mantra and it is always
> >> possible to e.g. pad options so you end up on aligned boundaries for the
> >> next header.
> >
> > fwiw, i'm not convinced that "most protocols of the IETF follow this
> > mantra". we've had multiple discussions in different protocol groups
> > about shaving or bloating by a few bytes here or there in different
> > protocols, and i don't think anyone has brought up memory alignment as
> > an argument in any of the discussions i've followed.
> >
>
> If the trade-off is between 1 padding byte and 2 byte alignment versus
> 3 padding bytes and 4 byte alignment I would definitely opt for 3
> padding bytes. I know how that waste feels like to a protocol
> designer, but I think it is worth it. Maybe the padding/reserved will
> be useful some day for an additional feature.
Note, if you do do this (hint, I think it is a good idea), require that
these reserved/pad fields always set to 0 for now, so that no one puts
garbage in them and then if you later want to use them, it will be a
mess.
thanks,
greg k-h
next prev parent reply other threads:[~2016-12-11 7:09 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-07 18:35 Jason A. Donenfeld
2016-12-07 18:47 ` Dave Taht
2016-12-07 18:51 ` David Miller
2016-12-07 18:54 ` Jason A. Donenfeld
2016-12-07 19:52 ` David Miller
2016-12-08 0:29 ` Jason A. Donenfeld
2016-12-08 0:37 ` David Miller
2016-12-08 22:20 ` Jason A. Donenfeld
2016-12-08 23:14 ` David Miller
2016-12-11 8:07 ` Willy Tarreau
2016-12-11 10:47 ` Måns Rullgård
2016-12-10 12:25 ` Felix Fietkau
2016-12-10 13:25 ` Måns Rullgård
2016-12-10 20:09 ` Felix Fietkau
2016-12-10 20:32 ` Måns Rullgård
2016-12-10 20:36 ` Felix Fietkau
2016-12-12 16:19 ` David Laight
2016-12-12 16:31 ` Måns Rullgård
2016-12-08 0:30 ` Hannes Frederic Sowa
2016-12-08 4:34 ` Daniel Kahn Gillmor
2016-12-09 11:26 ` Jiri Benc
2016-12-10 22:18 ` Dan Lüdtke
2016-12-11 7:15 ` Greg KH [this message]
2016-12-11 14:50 ` Jason A. Donenfeld
2016-12-11 15:30 ` Andrew Lunn
2016-12-11 15:37 ` Jason A. Donenfeld
2016-12-11 16:44 ` Willy Tarreau
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