Subject: Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG_DONE into same read() as families

From: Ido Schimmel <[email-masked]>
Date: Thu, 21 Mar 2024 19:41:28 +0200

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 <[email-masked]>

Sorry Eric, already sent the patch without your tag:

https://lore.kernel.org/netdev/[email-masked]/