netdev - Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG

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Date: Thu, 21 Mar 2024 19:41:28 +0200
From: Ido Schimmel <idosch@...sch.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Gal Pressman <gal.pressman@...ux.dev>, Jakub Kicinski <kuba@...nel.org>,
	Stefano Brivio <sbrivio@...hat.com>, davem@...emloft.net,
	netdev@...r.kernel.org, pabeni@...hat.com, jiri@...nulli.us,
	johannes@...solutions.net, fw@...len.de, pablo@...filter.org,
	Martin Pitt <mpitt@...hat.com>,
	Paul Holzinger <pholzing@...hat.com>,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG_DONE into same
 read() as families

On Thu, Mar 21, 2024 at 06:26:31PM +0100, Eric Dumazet wrote:
> The following seems to react quite differently :
> 
> # ip addr  show lo
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
> group default qlen 1000
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>     inet 127.0.0.1/8 scope host lo
>        valid_lft forever preferred_lft forever
>     inet6 ::1/128 scope host proto kernel_lo
>        valid_lft forever preferred_lft forever
> # ip link set dev lo mtu 1000
> # ip addr  show lo
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 1000 qdisc noqueue state UNKNOWN
> group default qlen 1000
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>     inet 127.0.0.1/8 scope host lo
>        valid_lft forever preferred_lft forever

Yes, for loopback the NETDEV_CHANGEMTU event is treated as NETDEV_DOWN
rather than NETDEV_UNREGISTER:

if (dev->mtu < IPV6_MIN_MTU) {
	addrconf_ifdown(dev, dev != net->loopback_dev);
	break;
}

vim net/ipv6/addrconf.c +3656

> Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Sorry Eric, already sent the patch without your tag:

https://lore.kernel.org/netdev/20240321173042.2151756-1-idosch@nvidia.com/