netdev - Re: [PATCH bpf-next v3 1/4] bpf: sock ops: add netns ino and dev in bpf context

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Date:   Mon, 29 Apr 2019 17:42:27 +0200
From:   Alban Crequy <alban@...volk.io>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Alban Crequy <alban.crequy@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Iago López Galeiras <iago@...volk.io>
Subject: Re: [PATCH bpf-next v3 1/4] bpf: sock ops: add netns ino and dev in
 bpf context

On Sat, Apr 27, 2019 at 8:39 PM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Sat, 27 Apr 2019 12:48:25 +0200, Alban Crequy wrote:
> > On Fri, Apr 26, 2019 at 11:03 PM Jakub Kicinski
> > <jakub.kicinski@...ronome.com> wrote:
> > >
> > > On Fri, 26 Apr 2019 17:48:45 +0200, Alban Crequy wrote:
> > > > In the unlikely case where network namespaces are not compiled in
> > > > (CONFIG_NET_NS=n), the verifier will not allow access to ->netns_*.
> > >
> > > Naive question - why return an error?  init_net should always be there,
> > > no?
> >
> > True for netns_dev. However, without CONFIG_NET_NS, we cannot access netns_ino:
> >
> > (struct sock_common).possible_net_t.(struct net *):
> >
> > typedef struct {
> > #ifdef CONFIG_NET_NS
> >         struct net *net;
> > #endif
> > } possible_net_t;
> >
> > And I don't think it would make much sense to allow access to
> > netns_dev but not netns_ino.
>
> Right, if CONFIG_NET_NS=n we could just take the pointer to init_net
> directly, and not worry about the field.  IMHO it'd be preferable to
> changing the UAPI based on kernel config, but I don't feel super
> strongly.

I see the point about not changing the UAPI. So I will update the patch to:
- return netns_dev unconditionally, regardless of CONFIG_NET_NS
- return netns_ino with either the correct value or zero depending on
CONFIG_NET_NS.