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

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Date:   Wed, 15 Feb 2017 20:35:15 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Tejun Heo <tj@...nel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 net] bpf: add bpf_sk_netns_id() helper

On 2/15/17 8:25 PM, Andy Lutomirski wrote:
> On Wed, Feb 15, 2017 at 7:18 PM, David Ahern <dsa@...ulusnetworks.com> wrote:
>> 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.
> 
> Why wouldn't an id relative to your logging program work?  Global ids
> are problematic because they are incompatible with tools like CRIU.
> 

How would that work?

To be specific with an example, I only want FIB lookups for network
namespace "foo". The name "foo" only has meaning for iproute2, so I need
something the kernel understands. Should that be a dev/inode match
meaning the tracepoints contain the netns dev and inode?

>From a perf perspective, the command line is like this:
   perf record -e fib:fib_table_lookup --filter="netns_dev == 3 &&
netns_ino == 4026531957" -a -g -- sleep 5

Cumbersome, but it would work if the tracepoints had netns_dev and
netns_ino as variables. A single id would be better.