netdev - Re: [PATCH bpf-next 3/7] bpf: add netns cookie and enable it for bpf cgroup hooks

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Date:   Fri, 27 Mar 2020 19:56:39 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     m@...bda.lt, joe@...d.net.nz, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 3/7] bpf: add netns cookie and enable it for bpf
 cgroup hooks

On Sat, Mar 28, 2020 at 03:16:06AM +0100, Daniel Borkmann wrote:
> On 3/28/20 2:48 AM, Alexei Starovoitov wrote:
> > On Fri, Mar 27, 2020 at 04:58:52PM +0100, Daniel Borkmann wrote:
> > > + *
> > > + * u64 bpf_get_netns_cookie(void *ctx)
> > > + * 	Description
> > > + * 		Retrieve the cookie (generated by the kernel) of the network
> > > + * 		namespace the input *ctx* is associated with. The network
> > > + * 		namespace cookie remains stable for its lifetime and provides
> > > + * 		a global identifier that can be assumed unique. If *ctx* is
> > > + * 		NULL, then the helper returns the cookie for the initial
> > > + * 		network namespace. The cookie itself is very similar to that
> > > + * 		of bpf_get_socket_cookie() helper, but for network namespaces
> > > + * 		instead of sockets.
> > 
> > All new helpers in this patch and few others are missing 'flags' argument.
> > Yes. It's kinda hard right now to come up with a use case for the flags,
> > since all helpers look kinda trivial, simple, and single purpose.
> > But the same thing happened with bpf_send_signal(). It felt that there is no
> > way to extend it. Yet later we had to add bpf_send_signal_thread() which could
> > have been handled with flags if they were there. So please add flags to all new
> > helpers though it might seem redundant.
> 
> We have very similar helpers for almost 2yrs now, that is, bpf_get_socket_cookie()
> and bpf_skb_ancestor_cgroup_id(). Both no extra 'unused flags' arg and they are
> simple enough to do exactly what we expect them to do, I also haven't seen any
> reason to extend them further so far (otherwise we have have new ones by now). The
> two added here are very much analogue to this, so breaking this consistency is
> super ugly just to add empty flags now. :/ Given the timeframe we have these by now
> and given they do one simple thing, what is the harm to add a new helper in future
> iff really needed rather than uglifying with flags now (I would understand it for
> complex helpers though where we use this practice)? Just recently we added bpf_jiffies64()
> (5576b991e9c1 ("bpf: Add BPF_FUNC_jiffies64")); no flag either and it has similar
> simplicity.

Fair enough, but I reserve the right to say "I told you so" later ;)
The series applied. Thanks.