linux-kernel - Re: [PATCH net-next 2/3] ipv6: per netns fib6 walkers

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Date:	Tue, 8 Mar 2016 08:05:44 +0100
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH net-next 2/3] ipv6: per netns fib6 walkers

On Mon, Mar 07, 2016 at 04:28:26PM -0800, Cong Wang wrote:
> On Mon, Mar 7, 2016 at 4:26 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Fri, Mar 4, 2016 at 2:59 AM, Michal Kubecek <mkubecek@...e.cz> wrote:
> >>  static void ipv6_route_seq_setup_walk(struct ipv6_route_iter *iter)
> >>  {
> >> +#ifdef CONFIG_NET_NS
> >> +       struct net *net = iter->p.net;
> >> +#else
> >> +       struct net *net = &init_net;
> >> +#endif
> >> +
> >
> > You should pass the struct net pointer to ipv6_route_seq_setup_walk()
> > instead of reading it by yourself.

I considered this. While it probably wouldn't bring any extra overhead
as the function is going to be inlined anyway, it didn't look really
nice. I gues I'll use read_pnet() as David suggested; I just didn't
realize the reason it's a macro in !CONFIG_NET_NS case is to allow
passing a pointer to non-existent struct member.

> > I don't find anyone actually using iter->p, it probably can be just removed.
> 
> Er, seq_file_net() uses it... but callers already call it.

Not only seq_file_net(). The whole infrastructure assumes private data
start with an instance of struct seq_net_private and seq_open_net()
initializes it.

                                                        Michal Kubecek