linux-kernel - Re: [PATCH v2] net/netfilter/x_tables.c: use __seq_open

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Message-ID: <54227D7D.6020909@codethink.co.uk>
Date:	Wed, 24 Sep 2014 09:14:53 +0100
From:	Rob Jones <rob.jones@...ethink.co.uk>
To:	Pablo Neira Ayuso <pablo@...filter.org>,
	Ben Hutchings <ben.hutchings@...ethink.co.uk>
CC:	davem@...emloft.net, coreteam@...filter.org,
	netdev@...r.kernel.org, linux-kernel@...ethink.co.uk,
	linux-kernel@...r.kernel.org, netfilter@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH v2] net/netfilter/x_tables.c: use __seq_open_private()



On 23/09/14 22:40, Pablo Neira Ayuso wrote:
> On Tue, Sep 23, 2014 at 06:46:27PM +0100, Ben Hutchings wrote:
>> On Tue, 2014-09-23 at 18:05 +0100, Rob Jones wrote:
>>> Reduce boilerplate code by using __seq_open_private() instead of seq_open()
>>> in xt_match_open() and xt_target_open().
>>>
>>> Signed-off-by: Rob Jones <rob.jones@...ethink.co.uk>
>>> ---
>>>
>>> This patch uses an existing variant of seq_open() to reduce the kernel code
>>> size.
>>>
>>> The only significant variation from the pre-existing code is the fact that
>>> __seq_open_private() calls kzalloc() rather than kmalloc(), which could
>>> conceivably have an impact on timing.
>>>
>>> This version 2 incorporates a minor initialisation simplification (resulting
>>> from kzalloc() being used) requested by netfilter-devel@...r.kernel.org
>> [...]
>>> --- a/net/netfilter/x_tables.c
>>> +++ b/net/netfilter/x_tables.c
>>> @@ -1080,7 +1080,6 @@ static void *xt_mttg_seq_start(struct seq_file *seq, loff_t *pos,
>>>          struct nf_mttg_trav *trav = seq->private;
>>>          unsigned int j;
>>>
>>> -       trav->class = MTTG_TRAV_INIT;
>>>          for (j = 0; j < *pos; ++j)
>>>                  if (xt_mttg_seq_next(seq, NULL, NULL, is_target) == NULL)
>>>                          return NULL;
>> [...]
>>
>> I'm fairly sure this simplification is wrong, as xt_mttg_seq_start() is
>> potentially called multiple times on the same file handle.

Well spotted Ben.

>
> Right. I'm going to take v1 of this patch instead, sorry for the
> inconvenience Rob.

No problem at all. It gave me something to do on the train home last
night :-)

-- 
Rob Jones
Codethink Ltd
mailto:rob.jones@...ethink.co.uk
tel:+44 161 236 5575
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