netdev - Re: [PATCH 2/2] ipv4: fix mss comparison

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Date:	Tue, 28 Feb 2012 17:55:41 +0800
From:	RongQing Li <roy.qing.li@...il.com>
To:	Francois Romieu <romieu@...zoreil.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] ipv4: fix mss comparison

2012/2/28 Francois Romieu <romieu@...zoreil.com>:
> roy.qing.li@...il.com <roy.qing.li@...il.com> :
> [...]
>> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
>> index 0489ced..c72f765 100644
>> --- a/net/ipv4/route.c
>> +++ b/net/ipv4/route.c
>> @@ -1914,8 +1914,8 @@ static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
>>       if (advmss == 0) {
>>               advmss = max_t(unsigned int, dst->dev->mtu - 40,
>>                              ip_rt_min_advmss);
>> -             if (advmss > 65535 - 40)
>> -                     advmss = 65535 - 40;
>> +             if (advmss > 65535 - sizeof(struct tcphdr))
>> +                     advmss = 65535 - sizeof(struct tcphdr);
>
> What would prevent net/ipv4/tcp_output.c::tcp_advertise_mss returning
> a value beyond 65535 - 40 ?
>

You are right, Please ignore this patch.
The biggest MSS should be (Total Length of ipv4 header -
sizeof(iphdr)- sizeof(tcphdr))

I mix up the Total Length of ipv4 header and Payload Length of ipv6 header.

> --
> Ueimor
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