netdev - Re: [PATCH net v3 0/2] ipv6: Fix listing and flushing of cached route exceptions

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Date:   Tue, 11 Jun 2019 00:47:58 +0200
From:   Stefano Brivio <sbrivio@...hat.com>
To:     David Ahern <dsahern@...il.com>, Martin KaFai Lau <kafai@...com>
Cc:     David Miller <davem@...emloft.net>, Jianlin Shi <jishi@...hat.com>,
        Wei Wang <weiwan@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net v3 0/2] ipv6: Fix listing and flushing of cached
 route exceptions

On Mon, 10 Jun 2019 23:53:15 +0200
Stefano Brivio <sbrivio@...hat.com> wrote:

> On Mon, 10 Jun 2019 15:38:06 -0600
> David Ahern <dsahern@...il.com> wrote:
> 
> > in dot releases of stable trees, I think it would be better to converge
> > on consistent behavior between v4 and v6. By that I mean without the
> > CLONED flag, no exceptions are returned (default FIB dump). With the
> > CLONED flag only exceptions are returned.  
> 
> Again, this needs a change in iproute2, because RTM_F_CLONED is *not*
> passed on 'flush'. And sure, let's *also* do that, but not everybody
> runs recent versions of iproute2.

One thing that sounds a bit more acceptable to me is:

- dump (in IPv4 and IPv6):
  - regular routes only, if !RTM_F_CLONED and NLM_F_MATCH
  - exceptions only, if RTM_F_CLONED and NLM_F_MATCH
  - everything if !NLM_F_MATCH

- fix iproute2 so that RTM_F_CLONED is passed on 'flush cache', or
  don't pass NLM_F_MATCH in that case

this way, the kernel respects the intended semantics of flags, and we
fix a bug in iproute2 (that was always present).

I think it's not ideal, because the kernel unexpectedly changed the
behaviour and we're not guaranteeing that older iproute2 works. The
fact it was broken for two years is probably a partial excuse for this,
though.

What do you think? I'll prepare a v4 for net-next if we all agree.

I'm not entirely sure which trees I should target. I guess this
introduces a feature in the kernel, so net-next, and fixes a bug in
iproute2, so iproute2.git?

-- 
Stefano