netdev - Re: [PATCH net-next 2/6] tunnels: PMTU discovery support for directly bridged IP packets

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Date:   Tue, 4 Aug 2020 07:53:14 +0200
From:   Stefano Brivio <sbrivio@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        Aaron Conole <aconole@...hat.com>,
        Numan Siddique <nusiddiq@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Pravin B Shelar <pshelar@....org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Lourdes Pedrajas <lu@...o.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/6] tunnels: PMTU discovery support for
 directly bridged IP packets

On Mon, 3 Aug 2020 17:44:16 -0600
David Ahern <dsahern@...il.com> wrote:

> On 8/3/20 2:52 PM, Stefano Brivio wrote:
> > @@ -461,6 +464,91 @@ static inline void iptunnel_xmit_stats(struct net_device *dev, int pkt_len)
> > [...]
> >
> > +static inline int skb_tunnel_check_pmtu(struct sk_buff *skb,
> > +					struct dst_entry *encap_dst,
> > +					int headroom, bool reply)  
> 
> Given its size, this is probably better as a function. I believe it can
> go into net/ipv4/ip_tunnel_core.c like you have iptunnel_pmtud_build_icmp.

Right, moved in v2.

> > [...]
> > +	if (skb->protocol == htons(ETH_P_IP) && mtu > 576) {  
> 
> I am surprised the 576 does not have an existing macro.

I guess that comes from how RFC 791 picks this "512 plus something
reasonable" value. I'll think of a name and propose as a later patch,
it's used in a number of places.

> > [...]
> > +		return iptunnel_pmtud_build_icmp(skb, mtu);
> > +	}
> > +#endif  
> 
> separate v4 and v6 code into helpers based on skb->protocol; the mtu
> check then becomes part of the version specific helpers.

Done.

> > +EXPORT_SYMBOL(iptunnel_pmtud_build_icmp);  
> 
> I think separate v4 and v6 versions would be more readable; the
> duplication is mostly skb manipulation.

Yes, way more readable, changed in v2.

-- 
Stefano