netdev - Re: Netfilter: New target: RLOG

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Message-ID: <20120119091248.GA32391@1984>
Date:	Thu, 19 Jan 2012 10:12:48 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Richard Weinberger <rw@...utronix.de>
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org
Subject: Re: Netfilter: New target: RLOG

Hi Richard,

On Wed, Jan 18, 2012 at 11:43:25PM +0100, Richard Weinberger wrote:
> RLOG is a new log target, it works like LOG with the exception that it writes to ring buffers.
> It makes use of Steven Rostedt's ring_buffer subsystem. 
> I've used Steve's ring buffer because it allows concurrent writes. IOW it's very fast.
> For more details see: Documentation/trace/ring-buffer-design.txt.
> 
> Each ring buffer is represented as a pipe-like file in /proc/net/netfilter/xt_RLOG/.
> You can read from it with and program you like (cat, syslog, etc...).
> The default size is 1MiB. With this size it can store approximately 5000 messages.
> 
> - Why not LOG?
> I like the LOG target a lot but I really hat it when it floods my kernel syslog.
> dmesg becomes useless.
> Writing all log messages to a file using syslogd also not always the best solution.
> Most of the time my firewall logs just waste disk space.
> 
> Compared with Steve's ring_buffer, the kernel syslog is rather slow.
> Especially when the firewall logs very much syslog becomes a bottleneck.
> As we all know printk() is not fast.
> 
> - Why not ULOG/NFLOG?
> Because it cannot replace LOG.
> Details like PHYSIN and PHYSOUT are not available form the packet headers.
> Also on many Linux systems ulogd is not available/supported.  

We only include physin and phyout if netfilter bridge is enabled. I
may be missing anything but, why can these be useful if bridging is not
enabled?

> - Why RLOG?
> Using RLOG you can have many ring buffers with all kind of logs.
> If your firewall goes nuts you don't have to mess you rule-set with adding
> new LOG rules to find out what's going on.
> Just install a few RLOG rules with small buffer sized and read them if you don't
> know what's going on.
> If you make you firewall rule-set per default verbose using LOG or NFLOG it will 
> generate lot's of useless messages which you'll never ever read.
> With RLOG you can bypass this problem.
> On my firewall I record only useful data to the disk. Everything else goes into RLOG.
> If your firewall is really busy and you want to log nearly everything, c
> reate a big ring buffer and read from is using your favorite userspace tool.
> In case the buffer fills faster than the userspace consumes it, RLOG will warn you.
> I'd also possible to resize the buffer.

I still think this can be useful.

But, why don't you add this to the LOG target as an extension instead
of yet another target?
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