netdev - Re: [PATCH] route:ip_rt_frag_needed always return unzero

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Date:	Wed, 19 Oct 2011 09:34:33 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] route:ip_rt_frag_needed always return unzero

2011.10.18 17:23, Eric Dumazet wrote:
> Le mardi 18 octobre 2011 à 15:04 +0800, Gao feng a écrit :
>> int function ip_rt_frag_need,if peer is null,
>> there is no need to do ipprot->err_handler.
>> I am right?
>>
>> Signed-off-by: Gao feng <gaofeng@...fujitsu.com>
>> ---
>>  net/ipv4/route.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
>> index 075212e..6cde0fa 100644
>> --- a/net/ipv4/route.c
>> +++ b/net/ipv4/route.c
>> @@ -1574,7 +1574,7 @@ unsigned short ip_rt_frag_needed(struct net *net, const struct iphdr *iph,
>>  
>>  		atomic_inc(&__rt_peer_genid);
>>  	}
>> -	return est_mtu ? : new_mtu;
>> +	return est_mtu;
>>  }
>>  
>>  static void check_peer_pmtu(struct dst_entry *dst, struct inet_peer *peer)
> 
> No idea why you want this, your changelog is a bit cryptic :)
> 
> Wont this bypass the raw_icmp_error(skb, protocol, info);
> call in icmp_unreach() as well ?
> 
> 

thanks Eric!

I mean that the pmtu is update by inet_peer->pmtu_learned as I know.
so in function ip_rt_frag_needed,
if inet_peer is null or someting else make the setting of inet_peer->pmtu_learned failed.
there is no need to call function tcp_v4_err.

the call stack is
icmp_unreach
  |
  |--->ip_rt_frag_needed(fill inet_peer)
  |
  |--->raw_icmp_error()
  |
  |--->ipprot->err_handler(tcp_v4_err or something else)
	|
	|--->tcp_v4_err(frag need icmp is triggered by tcp packet)
		|
		|--->do_pmtu_discovery
		(in this function both __sk_dst_check or dst->ops->update_pmtu
		need struct inet_peer to update pmtu)

so,I think when set inet_peer->pmtu_learned failed,
in func icmp_unreach we should goto out immediately.

And it's confuse me that why func ping_err and udp_err not update the pmtu?
What I miss?
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