netdev - Re: [PATCH net-next v3] net/ipv6: Introduce accept_unsolicited_na knob to implement router-side changes for RFC9131

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Date:   Wed, 13 Apr 2022 16:00:46 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Arun Ajith S <aajith@...sta.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, yoshfuji@...ux-ipv6.org,
        kuba@...nel.org, pabeni@...hat.com, corbet@....net,
        prestwoj@...il.com, gilligan@...sta.com, noureddine@...sta.com,
        gk@...sta.com
Subject: Re: [PATCH net-next v3] net/ipv6: Introduce accept_unsolicited_na
 knob to implement router-side changes for RFC9131

On 4/13/22 3:22 PM, Eric Dumazet wrote:
> 
> On 4/13/22 07:34, Arun Ajith S wrote:
>> Add a new neighbour cache entry in STALE state for routers on receiving
>> an unsolicited (gratuitous) neighbour advertisement with
>> target link-layer-address option specified.
>> This is similar to the arp_accept configuration for IPv4.
>> A new sysctl endpoint is created to turn on this behaviour:
>> /proc/sys/net/ipv6/conf/interface/accept_unsolicited_na.
> 
> 
> Do we really need to expose this to /proc/sys, for every interface added
> in the host ?
> 
> /proc files creations/deletion cost a lot in environments
> adding/deleting netns very often.

agree with the general intent (along with the increasing memory costs).
I do think this case should be done as a /proc/sys entry for consistency
with both ARP and existing related NA settings.

> 
> I would prefer using NETLINK attributes, a single recvmsg() syscall can
> fetch/set hundreds of them.

What do you have in mind here? A link attribute managed through `ip link
set`?