netdev - Re: [PATCH net] ipv6: fix src addr routing with the exception table

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Date:   Wed, 15 May 2019 10:45:34 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Wei Wang <tracywwnj@...il.com>, David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Mikael Magnusson <mikael.kernel@...ts.m7n.se>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] ipv6: fix src addr routing with the exception table

From: David Ahern <dsahern@...il.com>
Date: Wed, May 15, 2019 at 10:33 AM
To: Wei Wang
Cc: Wei Wang, David Miller, Linux Kernel Network Developers, Martin
KaFai Lau, Mikael Magnusson, Eric Dumazet

> On 5/15/19 11:28 AM, Wei Wang wrote:
> > From: Wei Wang <weiwan@...gle.com>
> > Date: Wed, May 15, 2019 at 10:25 AM
> > To: David Ahern
> > Cc: Wei Wang, David Miller, Linux Kernel Network Developers, Martin
> > KaFai Lau, Mikael Magnusson, Eric Dumazet
> >
> >>>
> >>> What about rt6_remove_exception_rt?
> >>>
> >>> You can add a 'cache' hook to ip/iproute.c to delete the cached routes
> >>> and verify that it works. I seem to have misplaced my patch to do it.
> >> I don't think rt6_remove_exception_rt() needs any change.
> >> It is because it gets the route cache rt6_info as the input parameter,
> >> not specific saddr or daddr from a flow or a packet.
> >> It is guaranteed that the hash used in the exception table is
> >> generated from rt6_info->rt6i_dst and rt6_info->rt6i_src.
> >>
> >> For the case where user tries to delete a cache route, ip6_route_del()
> >> calls rt6_find_cached_rt() to find the cached route first. And
> >> rt6_find_cached_rt() is taken care of to find the cached route
> >> according to both passed in src addr and f6i->fib6_src.
> >> So I think we are good here.
> >>
> >> From: David Ahern <dsahern@...il.com>
> >> Date: Wed, May 15, 2019 at 9:38 AM
> >> To: Wei Wang, David Miller, <netdev@...r.kernel.org>
> >> Cc: Martin KaFai Lau, Wei Wang, Mikael Magnusson, Eric Dumazet
> >>
> >>> On 5/15/19 9:56 AM, David Ahern wrote:
> >>>> You can add a 'cache' hook to ip/iproute.c to delete the cached routes
> >>>> and verify that it works. I seem to have misplaced my patch to do it.
> >>>
> >>> found it.
> >
> > Thanks. I patched it to iproute2 and tried it.
> > The route cache is removed by doing:
> > ip netns exec a ./ip -6 route del fd01::c from fd00::a cache
> >
>
> you have to pass in a device. The first line in ip6_del_cached_rt:
>
> if (cfg->fc_ifindex && rt->dst.dev->ifindex != cfg->fc_ifindex)
>                 goto out;
>
> 'ip route get' is one way to check if it has been deleted. We really
> need to add support for dumping exception routes.

Without passing in dev, fc_ifindex = 0. So it won't goto out. Isn't it?
The way I checked if the route cache is being removed is by doing:
ip netns exec a cat /proc/net/rt6_stats
The 5th counter is the number of cached routes right now in the system.

The output I get after I run the reproducer:
# ip netns exec a cat /proc/net/rt6_stats
000b 0006 000e 0006 0001 0005 0000
# ip netns exec a ./ip -6 route del fd01::c from fd00::/64 cache
# ip netns exec a cat /proc/net/rt6_stats
000b 0006 0012 0006 0000 0004 0000

The same behavior if I pass in dev:
# ip netns exec a cat /proc/net/rt6_stats
000b 0006 000c 0006 0001 0004 0000
# ip netns exec a ./ip -6 route del fd01::c from fd00::/64 dev vethab cache
# ip netns exec a cat /proc/net/rt6_stats
000b 0006 0013 0006 0000 0003 0000