netdev - rp_filter backward compatibility

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Date:	Mon, 30 Aug 2010 17:25:22 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	netdev <netdev@...r.kernel.org>
CC:	David Miller <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...tta.com>
Subject: rp_filter backward compatibility

I'm surprised by the commit 27fed4175acf81ddd91d9a4ee2fd298981f60295 (ip: fix 
logic of reverse path filter sysctl). This commit breaks backward compatibility.
I know that logic was wrong, but for years it was mandatory to set both 
all.rp_filter and <device>.rp_filter to enable it, ie setting only all.rp_filter 
had no consequences. Now, when all.rp_filter is enabled, RPF is enabled for all 
interfaces.
Help of Kconfig explains:

                                                                 "To turn
           rp_filter on use:

           echo 1 > /proc/sys/net/ipv4/conf/<device>/rp_filter
            *and*
           echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter"

At least, one of this action should be done:
  - fixing help (Documentation/networking/ip-sysctl.txt is up to date)
  - reverting the patch (this will force to set all.rp_filter to 3 if some 
interfaces use loose mode and some others strict mode)

What is your opinion?

Regards,
Nicolas
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