netdev - Re: [PATCH] ipv6: ip6_append_data_mtu do not handle the mtu of the second fragment properly

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Date:	Wed, 12 Mar 2014 11:26:46 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	lucien xin <lucien.xin@...il.com>
Cc:	network dev <netdev@...r.kernel.org>,
	Gao feng <gaofeng@...fujitsu.com>
Subject: Re: [PATCH] ipv6: ip6_append_data_mtu do not handle the mtu of the second fragment properly

On Wed, Mar 12, 2014 at 10:40:50AM +0800, lucien xin wrote:
> but I cannot understand the top half of ip6_append_data() has the code
> to get mtu,
>                 if (rt->dst.flags & DST_XFRM_TUNNEL)
>                         mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
>                               rt->dst.dev->mtu : dst_mtu(&rt->dst);
>                 else
>                         mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
>                               rt->dst.dev->mtu : dst_mtu(rt->dst.path);
> 
>  why it need to calculate mtu again?  just "mtu=*mtu +
> rt->dst.header_len", isn't it sufficient?

It would be possible if we are absolutely sure if we don't call
ip6_append_data_mtu a second time, which I have not yet reviewed.

The line I proposed above may also suffer from this problem.

Maybe you already checked that?

Greetings,

  Hannes

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