netdev - Re: [PATCH v2 net-next] net: neigh: add netlink filtering based on LLADDR for dump

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Message-ID: <d8a28a59-79ca-e1fc-7768-a91f8033ce0e@kernel.org>
Date:   Wed, 25 May 2022 09:19:33 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Florent Fourcot <florent.fourcot@...irst.fr>,
        netdev@...r.kernel.org
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH v2 net-next] net: neigh: add netlink filtering based on
 LLADDR for dump

On 5/24/22 2:49 PM, Florent Fourcot wrote:
> Hello David,
> 
> This patch has been marked as rejected after your comment.
> Could you perhaps have a second look on it? And on my response above? I
> still think that my patch is relevant and add a currently not available
> feature.
> 
> I can work on alternative approach if necessary. Since neighbour tables
> are sometimes huge, performance overhead of userspace filtering for a
> simple MAC address lookup is currently high. And GET does not provide
> same feature.
> 

Kernel side filtering has always been kept to simple, coarse grained
checks - like a device index or upper device index. It's a fine line
managing kernel cycles holding the rtnl vs cycles shipping the data to
userspace. e.g., a memcmp has a higher cost than a dev->index
comparison. I see the point about GET only - potential for many matches
and a lookup of the ll address is basically a filtered dump. Mixed
thoughts on whether this should be merged.