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

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Date:	Thu, 04 Mar 2010 13:15:11 +0200
From:	Timo Teräs <timo.teras@....fi>
To:	Patrick McHardy <kaber@...sh.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] ipv4: flush ARP entries on device change

Patrick McHardy wrote:
> 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.

Ok.

Should I make a patch that uses dev->priv_flags and repost?

Or would make sense to have more generic way, e.g. keep copy
of the previous flags in struct net_device so notifiers can
check which ones changed (or would this have locking issues?).

- Timo
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