netdev - Re: [PATCH net V2] Exempt multicast addresses from five-second neighbor lifetime

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Date:   Tue, 10 Nov 2020 09:21:53 -0500
From:   Jeff Dike <jdike@...mai.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, David Ahern <dsahern@...il.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>
Subject: Re: [PATCH net V2] Exempt multicast addresses from five-second
 neighbor lifetime

Hi Jakub,

On 11/9/20 2:47 PM, Jakub Kicinski wrote:
> This makes sense because mcast L2 addr is calculated, not discovered,
> and therefore can be recreated at a very low cost, correct?

Yes.

> Perhaps it would make sense to widen the API to any "computed" address
> rather than implicitly depending on this behavior for mcast?

I'm happy to do that, but I don't know of any other types of addresses which are computed and end up in the neighbors table.

> I'm not an expert tho, maybe others disagree.
> 
>> +static int arp_is_multicast(const void *pkey)
>> +{
>> +	return IN_MULTICAST(htonl(*((u32 *)pkey)));
>> +}
> 
> net/ipv4/arp.c:935:16: warning: cast from restricted __be32
> 
> s/u32/__be32/
> s/htonl/ntohl/

Thanks, I ran sparse, but must have missed that somehow.

Jeff