netdev - Re: wireless vs. alignment requirements

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Message-ID: <20071125140121.GA12665@gondor.apana.org.au>
Date:	Sun, 25 Nov 2007 22:01:21 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	dsd@...too.org, davem@...emloft.net, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org
Subject: Re: wireless vs. alignment requirements

On Sun, Nov 25, 2007 at 02:54:24PM +0100, Johannes Berg wrote:
>
> But I do have a choice where to fix it up and I'd prefer the drivers to
> do it where necessary. For that, the warning would work because it'd
> show driver authors that they need to fix something.

Fair enough.

> Hmm. I don't think so. Take an AP for example. It gets a lot of packets
> from stations. Now, if you're not QoS capable then all is well. But i
> you are and some stations are as well then all those stations send QoS
> packets (+2 bytes). Or take an AP connected via wireless (WPS), WPS has
> +6 bytes so I get all incoming upstream traffic with such unaligned
> headers.

The question is does this actually change all the time.  Let's
say you took a random sample of a second worth of IP packets
over wireless, what proportion of them are going to have the
same hardware header length modulo 4?

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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