netdev - Re: [PATCH v2 net-next] arp: flush arp cache on IFF

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Message-ID: <1369153519.2615.3.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Tue, 21 May 2013 17:25:19 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Timo Teräs <timo.teras@....fi>
CC:	David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
	<kaber@...sh.net>
Subject: Re: [PATCH v2 net-next] arp: flush arp cache on IFF_NOARP change

On Tue, 2013-05-21 at 13:23 +0300, Timo Teräs wrote:
> IFF_NOARP affects what kind of neighbor entries are created
> (nud NOARP or nud INCOMPLETE). If the flag changes, flush the arp
> cache to refresh all entries.
> 
> Signed-off-by: Timo Teräs <timo.teras@....fi>
> ---
> > This patch makes no sense at all.
> > 
> > The state bit in ->priv_flags is a boolean stating whether the
> > notified should do something or not.
> > 
> > But you're setting it to match what IFF_NOARP is.
> >
> > You should set it any time IFF_NOARP _changes_, and then clear
> > the bit when the notifier clears the neighbour entries.
> 
> IFF_NOARP_CHANGED is set according to "changes = dev->flags ^ old_flags;"
> which reflect the change. But I agree that the clearing out bit was
> misplaced. This is especially true as it seems NETDEV_CHANGE can be
> notified from another place too.
[...]

None of the other persistent flags have a transient flag for changes;
why should IFF_NOARP?  Why not cache the IFF_NOARP state in the
in_device and then compare and update that in arp_netdev_event().

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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