netdev - Re: [PATCH bpf] bpf: Support sk lookup in netns with id 0

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Message-ID: <20181127211155.63gigvcnyohzae6e@ast-mbp.dhcp.thefacebook.com>
Date:   Tue, 27 Nov 2018 13:11:57 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Joe Stringer <joe@...d.net.nz>
Cc:     Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        David Ahern <dsahern@...il.com>, daniel@...earbox.net,
        ast@...nel.org, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf] bpf: Support sk lookup in netns with id 0

On Tue, Nov 27, 2018 at 10:01:40AM -0800, Joe Stringer wrote:
> On Tue, 27 Nov 2018 at 06:49, Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
> >
> > Le 26/11/2018 à 23:08, David Ahern a écrit :
> > > On 11/26/18 2:27 PM, Joe Stringer wrote:
> > >> @@ -2405,6 +2407,9 @@ enum bpf_func_id {
> > >>  /* BPF_FUNC_perf_event_output for sk_buff input context. */
> > >>  #define BPF_F_CTXLEN_MASK           (0xfffffULL << 32)
> > >>
> > >> +/* BPF_FUNC_sk_lookup_tcp and BPF_FUNC_sk_lookup_udp flags. */
> > >> +#define BPF_F_SK_CURRENT_NS         0x80000000 /* For netns field */
> > >> +
> > >
> > > I went down the nsid road because it will be needed for other use cases
> > > (e.g., device lookups), and we should have a general API for network
> > > namespaces. Given that, I think the _SK should be dropped from the name.
> 
> Fair point, I'll drop _SK from the name
> 
> > >
> > Would it not be possible to have a s32 instead of an u32 for the coming APIs?
> > It would be better to match the current netlink and kernel APIs.
> 
> Sure, I'll look into this.
> 
> I had earlier considered whether it's worth attempting to leave the
> upper 32 bits of this parameter open for potential future expansion,
> but at this point I'm not taking that into consideration. If anyone
> has preferences or thoughts on that I'd be interested to hear them.

Can we keep u64 as an argument type and do
if ((s32)netns_id < 0) {
  net = caller_net;
} else {
  if (netns_id > S32_MAX)
    goto err;
  net = get_net_ns_by_id(caller_net, netns_id);
}

No need for extra macro in such case and passing -1 would match the rest of the kernel.
Upper 32-bit would still be open for future expansion.