netdev - Re: [net-next fragmentation icmp v4 3/4] bridge_netfilter: No ICMP packet on IPv4 defragmentation timeout

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Date:	Thu, 14 May 2015 17:42:49 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	azhou@...ira.com
Cc:	fw@...len.de, netdev@...r.kernel.org
Subject: Re: [net-next fragmentation icmp v4 3/4] bridge_netfilter: No ICMP
 packet on IPv4 defragmentation timeout

From: Andy Zhou <azhou@...ira.com>
Date: Thu, 14 May 2015 12:54:23 -0700

> On Thu, May 14, 2015 at 1:59 AM, Florian Westphal <fw@...len.de> wrote:
>> Andy Zhou <azhou@...ira.com> wrote:
>>> Currently, on defragmentation timeout error, ICMP error message
>>> will be generated. This is fine when they are used in a routing context,
>>> but does not make sense in the context of bridging netfilter.
>>>
>>> This patch adds a bit (IPSKB_NO_FRAG_ICMP) in IPCB to control
>>> whether ICMP error message should be generated. br_netfiler sets
>>> this bit.
>>
>> Could you please explain why we need this patch?
>> After the previous change (patch 2 in your series), we will already
>> bail out before hitting
>>
>> /* Send an ICMP "Fragment Reassembly Timeout" message. */
>> icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
>>
>> in ip_expire() based on qp->user value test?
> 
> Letting caller making the decision seems to be a better design choice
> rather than implicit
> logic embedded within the function.  It is also more flexible and
> robust when we need to extend 'user'
> range down the road.

You're doing useless testing for a hypothetical situation which may
never come to fruitation at all.

I don't think that ever qualifies as a legitimate objection.
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