netdev - Re: [PATCH net-next 03/14] gtp: Call common functions to get tunnel routes and add dst

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Date:   Tue, 19 Sep 2017 09:05:18 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     David Miller <davem@...emloft.net>
Cc:     Tom Herbert <tom@...ntonium.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Harald Welte <laforge@...monks.org>,
        Rohit Seth <rohit@...ntonium.net>
Subject: Re: [PATCH net-next 03/14] gtp: Call common functions to get tunnel
 routes and add dst_cache

On Mon, Sep 18, 2017 at 9:17 PM, David Miller <davem@...emloft.net> wrote:
> From: Tom Herbert <tom@...ntonium.net>
> Date: Mon, 18 Sep 2017 17:38:53 -0700
>
>> Call ip_tunnel_get_route and dst_cache to pdp context which should
>> improve performance by obviating the need to perform a route lookup
>> on every packet.
>>
>> Signed-off-by: Tom Herbert <tom@...ntonium.net>
>
> Not caused by your changes, but something to think about:
>
>> -static struct rtable *ip4_route_output_gtp(struct flowi4 *fl4,
>> -                                        const struct sock *sk,
>> -                                        __be32 daddr)
>> -{
>> -     memset(fl4, 0, sizeof(*fl4));
>> -     fl4->flowi4_oif         = sk->sk_bound_dev_if;
>> -     fl4->daddr              = daddr;
>> -     fl4->saddr              = inet_sk(sk)->inet_saddr;
>> -     fl4->flowi4_tos         = RT_CONN_FLAGS(sk);
>> -     fl4->flowi4_proto       = sk->sk_protocol;
>> -
>> -     return ip_route_output_key(sock_net(sk), fl4);
>> -}
>
> This and the new dst caching code ignores any source address selection
> done by ip_route_output_key() or the new tunnel route lookup helpers.
>
> Either source address selection should be respected, or if saddr will
> never be modified by a route lookup for some specific reason here,
> that should be documented.

Yes, I noticed that. In this case the source address is intended to be
taken bound on the socket which would imply we aren't interested in
source address selection.

Tom