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

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Date:	Wed, 03 Mar 2010 15:33:59 +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 Teras wrote:
>>> If device flag IFF_NOARP is changed, we should flush the ARP cache as
>>> all
>>> entries need to get refreshed.
>>>
>>> Signed-off-by: Timo Teras <timo.teras@....fi>
>>> ---
>>>  net/ipv4/arp.c |    3 +++
>>>  1 files changed, 3 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
>>> index c4dd135..036da92 100644
>>> --- a/net/ipv4/arp.c
>>> +++ b/net/ipv4/arp.c
>>> @@ -1245,6 +1245,9 @@ static int arp_netdev_event(struct
>>> notifier_block *this, unsigned long event, vo
>>>          neigh_changeaddr(&arp_tbl, dev);
>>>          rt_cache_flush(dev_net(dev), 0);
>>>          break;
>>> +    case NETDEV_CHANGE:
>>> +        neigh_changeaddr(&arp_tbl, dev);
>>> +        break;
>>
>> 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.
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