netdev - Re: [PATCH]: fix lro_gen

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Date:	Sat, 1 Dec 2007 09:34:57 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Andrew Gallatin <gallatin@...i.com>
Cc:	Roland Dreier <rdreier@...co.com>, davem@...emloft.net,
	ossthema@...ibm.com, netdev@...r.kernel.org
Subject: Re: [PATCH]: fix lro_gen_skb() alignment

On Fri, Nov 30, 2007 at 02:35:43PM -0500, Andrew Gallatin wrote:
>
> >Isn't the value of 2 ethernet-specific (to round the 14-byte header up
> >to 16)?  Given that the rest of the lro code is fairly careful to
> >calculate mac_hdr_len etc it seems as if it would be cleaner to make
> >this independent of the specific L2 being used.
> >
> >(And I plan on using the LRO module for IP-over-InfiniBand so this is
> >not completely theoretical)

Good point!

We really should rename NET_IP_ALIGN so that both Ethernet and DMA
occur in it somehow :)

> Good point.  I tend to think all the world is ethernet.
> Perhaps the better way would be to simply add an alignment pad
> field to lro_mgr?  When the driver initializes it, it specifies
> any padding needed.  Ethernet drivers would specify 2.

Just pass in the mac_hdr_len, and calculate the padding as

	ALIGN(mac_hdr_len, 4) - mac_hdr_len

or even simpler

	~(mac_hdr_len - 1) & 3

Bonus points for putting this in a macro alongside NET_IP_ALIGN :)

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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