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

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Date:	Tue, 23 Sep 2014 18:46:27 +0100
From:	Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:	Rob Jones <rob.jones@...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 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.

Ben.


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