netdev - Re: [PATCH 2/2] ipv4: flush ARP entries on device change

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Date:	Wed, 03 Mar 2010 15:44:49 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Timo Teräs <timo.teras@....fi>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] ipv4: flush ARP entries on device change

Timo Teräs wrote:
> Patrick McHardy wrote:
>> Timo Teräs wrote:
>>> Patrick McHardy wrote:
>>>> Timo Teras wrote:
>>>> It would be nice if we could restrict this to IFF_NOARP changes.
>>> Yes. But I did not see any easy way to figure out which flags have
>>> changed.
>>>
>>> Should we just keep a copy of the previous IFF_NOARP bit somewhere
>>> (where?).
>>> Or did I miss something obvious?
>>
>> We shouldn't have any arp entries for devices with IFF_NOARP set,
>> so perhaps we can flush only in that case. The transition IFF_NOARP
>> -> ~IFF_NOARP shouldn't need flushing.
> 
> IFF_NOARP devices do have neighbor entries with the nud NOARP.
> Exactly those entries I want to flush when IFF_NOARP flag is
> removed.
> 
> You can see those entries with "ip neigh show nud all". You have
> them e.g. for loopback stuff and broad-/multicast stuff in general.
> With IFF_NOARP you get them on all unicast addresses used.

I see. I don't have a better suggestion, except perhaps
to store the bit in dev->priv_flags.
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