netdev - Re: [PATCH] ip: find correct route for socket which is not bound (v2)

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Date:	Thu, 8 Oct 2015 11:31:05 +0800
From:	Wengang Wang <wen.gang.wang@...cle.com>
To:	Wengang Wang <wen.gang.wang@...cle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] ip: find correct route for socket which is not bound (v2)

Hi,

Any comment on this patch?

thanks,
wengang

在 2015年09月25日 09:52, Wengang Wang 写道:
> This is the v2, comparing the v1, the changes is:
>   * for loopback outbound device, it continue skipping cached route;
>     for others, it goes through the cached route.
>
> For multicast, we should find valid route(thus get the meaniful pmtu) for
> the packet on the socket which is not bound to a device(sk_bound_dev_if
> being 0) too.
>
>  From man page of socket(7)
>
>         SO_BINDTODEVICE
> 		Bind this socket to a particular device like “eth0”, as
> 		specified in the passed interface name.  If the name is an
> 		empty string or the option length is zero, the socket
> 		device binding is removed. The  passed  option is  a
> 		variable-length null-terminated interface name string with
> 		the maximum size of IFNAMSIZ.  If a socket is bound to an
> 		interface, only packets received from that particular
> 		interface are processed by the socket. Note that this works
> 		only for some socket types, particularly AF_INET sockets.
> 		It is not supported for packet sockets (use normal bind(2)
> 		there).
>
> The man page doesn't say when socket not bound packets won't be routed.
>
> A problem is hit that all multicast packets dropped by kernel(from sender
> host). The lower layer is IPoIB with MTU being 7000. And I was sending 4096
> length multicast  packets. Inside IPoIB the first send is dropped because
> is exeeding the internal packet size limitation mcast_mtu which is 2044.
> So IPoIB calls ip_rt_update_pmtu (indirectly) trying to set path mtu. A
> correct route is configured for the multicast, so the setting of pmtu
> cucceeded and the next multicast packet(to the same target) is expected
> to succeed(it would be well fragmented accroding to the pmtu I just set).
> But actually the second and later multicast packets got dropped too. And
> the reason is that the neighor looking up(fib_lookup) is skipped because of
> the socket is not bound to device(sk_bound_dev_if being 0). After applied
> the patch I proposed here, it works fine.
>
> Signed-off-by: Wengang Wang <wen.gang.wang@...cle.com>
> ---
>   net/ipv4/route.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index 5f4a556..c0534c2 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -2097,7 +2097,10 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
>   			 */
>   
>   			fl4->flowi4_oif = dev_out->ifindex;
> -			goto make_route;
> +			if (dev_out->flags & IFF_LOOPBACK)
> +				goto make_route;
> +			else
> +				goto lookup;
>   		}
>   
>   		if (!(fl4->flowi4_flags & FLOWI_FLAG_ANYSRC)) {
> @@ -2153,6 +2156,7 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
>   		goto make_route;
>   	}
>   
> +lookup:
>   	if (fib_lookup(net, fl4, &res, 0)) {
>   		res.fi = NULL;
>   		res.table = NULL;

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