netdev - Re: GRO/GSO hiding PMTU?

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Message-Id: <20110210.230712.183040908.davem@davemloft.net>
Date:	Thu, 10 Feb 2011 23:07:12 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: GRO/GSO hiding PMTU?

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Fri, 11 Feb 2011 17:37:53 +1100

> What I wanted to do if I ever get enough time to work on this is
> to record the transport header length in a gso_hlen field so we
> can fix this properly.
> 
> We currently have a useless gso_segs field that only has one or
> two users that don't even need it.  We could easily get rid of it
> and use that space for gso_hlen instead.
> 
> The gso_hlen field only needs to be filled in at the few spots
> that generate GSO packets, i.e.,
> 
> 1) TCP
> 2) Virt backends like tun.c
> 3) GRO

Yep, that's good idea.

And even if we needed to add one more u32 to skb_shared_info()
that's still sort-of "free" because of SLAB slack space.

I'll look into doing this.

Thanks!
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