netdev - Re: [PATCH v3 net] net, ip6_tunnel: enhance tunnel locate with link check

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Message-ID: <ce1f9fbe-a28a-d5c3-c792-ded028df52e5@6wind.com>
Date:   Wed, 12 Feb 2020 16:54:19 +0100
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     William Dauchy <w.dauchy@...teo.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v3 net] net, ip6_tunnel: enhance tunnel locate with link
 check

Le 12/02/2020 à 09:30, William Dauchy a écrit :
[snip]
> @@ -1848,6 +1870,11 @@ ip6_tnl_dev_init_gen(struct net_device *dev)
>  	dev->type = ARPHRD_TUNNEL6;
>  	dev->hard_header_len = LL_MAX_HEADER + t_hlen;
>  	dev->mtu = ETH_DATA_LEN - t_hlen;
> +	if (t->parms.link) {
> +		tdev = __dev_get_by_index(t->net, t->parms.link);
> +		if (tdev && tdev->mtu < dev->mtu)
> +			dev->mtu = tdev->mtu;
Hmm, I was expecting 'tdev->mtu - t_hlen'. Am I wrong?

In fact, something like this:
dev->mtu = ETH_DATA_LEN - t_hlen;
if (t->parms.link) {
	tdev = __dev_get_by_index(t->net, t->parms.link);
	if (tdev)
		dev->mtu = tdev->mtu - t_hlen;
}

With ipip:
$ ip l s eth1 mtu 2000
$ ip link add ipip1 type ipip remote 10.16.0.121 local 10.16.0.249 dev eth1
$ ip l
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 2000 qdisc pfifo_fast state UP
mode DEFAULT group default qlen 1000
...
10: ipip1@...1: <POINTOPOINT,NOARP> mtu 1980 qdisc noop state DOWN mode DEFAULT
group default qlen 1000