netdev - Re: [PATCH v4 net] bpf: add bpf_sk_netns

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Date:   Wed, 15 Feb 2017 20:18:41 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Tejun Heo <tj@...nel.org>,
        Andy Lutomirski <luto@...capital.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v4 net] bpf: add bpf_sk_netns_id() helper

On 2/15/17 8:08 PM, Eric W. Biederman wrote:
> David Ahern <dsa@...ulusnetworks.com> writes:
> 
>> On 2/14/17 12:21 AM, Eric W. Biederman wrote:
>>>> in cases where bpf programs are looking at sockets and packets
>>>> that belong to different netns, it could be useful to get an id
>>>> that uniquely identify a netns within the whole system.
>>> It could be useful but there is no unique namespace id.
>>>
>>
>> Have you given thought to a unique namespace id? Networking tracepoints
>> for example could really benefit from a unique id.
> 
> An id from the perspective of a process in the initial instance of every
> namespace is certainly possible.
> 
> A truly unique id is just not maintainable.  Think of the question how
> do you assign every device in the world a rguaranteed unique ip address
> without coordination, that is routable.  It is essentially the same
> problem.
> 
> AKA it is theoretically possible and very expensive.  It is much easier
> and much more maintainable for identifiers to have scope and only be
> unique within that scope.


I don't mean unique in the entire world, I mean unique within a single
system.

Tracepoints are code based and have global scope. I would like to be
able to correlate, for example, FIB lookups within a single network
namespace. Having an id that I could filter on when collecting or match
when dumping them goes a long way.