netdev - Re: [PATCH] net: neighbour table ABI problem

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Message-Id: <20080521.133510.145260976.davem@davemloft.net>
Date:	Wed, 21 May 2008 13:35:10 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	kaber@...sh.net, tgraf@...g.ch, Stephane_Chazelas@...oo.fr,
	netdev@...r.kernel.org
Subject: Re: [PATCH] net: neighbour table ABI problem

From: Stephen Hemminger <shemminger@...tta.com>
Date: Wed, 21 May 2008 10:40:19 -0700

> The neighbor table time of last use information is returned in the incorrect
> unit. Kernel to user space ABI's need to use USER_HZ (or milliseconds), otherwise
> the application has to try and discover the real system HZ value which is problematic.
> Linux has standardized on keeping USER_HZ consistent (100hz) even when kernel is
> running internally at some other value.
> 
> This change is small, but it breaks the ABI for older version of iproute2 utilities.
> But these utilities are already broken since they are looking at the psched_hz values
> which are completely different. So let's just go ahead and fix both kernel and user
> space. Older utilities will just print wrong values.
> 
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>

In at least one sense the kernel has been providing a consistent
value :-)

I don't know what to do here, it's different from the other patch
you posted today in that I can't see any easy way to not change
behavior for old stuff.

Can we add a new attribute or something like that?
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