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

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Message-ID: <20140923214021.GA4206@salvia>
Date:	Tue, 23 Sep 2014 23:40:21 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Ben Hutchings <ben.hutchings@...ethink.co.uk>
Cc:	Rob Jones <rob.jones@...ethink.co.uk>, 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 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.

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