netdev - Re: [PATCH 1/2] netlink: netlink_dump_start may take data pointer for callbacks

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Date:	Sat, 25 Feb 2012 00:18:03 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 1/2] netlink: netlink_dump_start may take data pointer
 for callbacks

On Fri, Feb 24, 2012 at 05:47:26PM -0500, David Miller wrote:
> From: pablo@...filter.org
> Date: Fri, 24 Feb 2012 23:14:07 +0100
> 
> > From: Pablo Neira Ayuso <pablo@...filter.org>
> > 
> > This patch modifies the netlink_dump_start function to take one
> > generic pointer to data. This pointer can be used inside the
> > dump() and done() callbacks via cb->data.
> > 
> > Netfilter is going to use this patch to provide filtered dumps
> > to user-space. This is specifically interesting in ctnetlink that
> > may handle lots of conntrack entries. We can save precious
> > cycles by skipping the conversion to TLV format of conntrack
> > entries that are not interesting for user-space.
> > 
> > More specifically, ctnetlink will include one operation to allow
> > to filter the dumping of conntrack entries by ctmark values.
> > 
> > Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> 
> This isn't really your fault but netlink_dump_start() has an
> enormous number of arguments.
> 
> Several of them are zero or NULL in all except one special situation.
> 
> An entire argument is a lot of overhead for one situation to impose on
> all the others.
> 
> I have no objection to the data callback scheme, it's just that
> the argument list of this interface is getting out of control.
> 
> Usually, in situations like this, we have some control structure
> that holds all the control state and we pass that in instead.
> 
> 	struct netlink_dump_control c = { .dump = dump, .done = done, ... };
> 
> 	netlink_dump_start(..., &c);
> 
> It could be perhaps used here to get things back under control.

OK, I'll send a patch to make it like this.
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