Date:	Mon, 23 Mar 2015 10:41:46 +0100
From:	Jeremias Blendin <jeremias@...ndin.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	containers@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: Get statistics from all network interfaces on a system, including
 those inside network namespaces

2015-03-21 22:32 GMT+01:00 Eric W. Biederman <ebiederm@...ssion.com>:
> Jeremias Blendin <jeremias@...ndin.org> writes:
>
>> Thank you for the detailed answer!
>>
>> See also my comments below:
>>
>> 2015-03-20 21:10 GMT+01:00 Eric W. Biederman <ebiederm@...ssion.com>:
>>> Jeremias Blendin <jeremias@...ndin.org> writes:
>>>
>>>> Hi,
>>>>
>>>> I hope this is the right list to post this question.
>>>
>>> This list and netdev are the right lists.  It is one of those
>>> overlapping topics.
>>>
>>> Right now I find applications dealing with multiple network namespaces
>>> interesting as the APIs are a little rough and it is time to knock off
>>> some of the rough edges.
>>>
>>>> Currently, we are using a patched version of bwm-ng to poll statistics
>>>> of network interfaces. Some of these interfaces are located inside
>>>> network namespaces, unfortunately we have found no way to poll all
>>>> interfaces from all netspaces at once, without making our client
>>>> application process traverse through all the available network
>>>> namespaces (one result is this patch for bwm-ng:
>>>> https://github.com/jgjl/bwm-ng/tree/lxns).
>>>> Is there a more efficient way (for example by using netlink directly)
>>>> to get a complete list of the statistics of all network interfaces
>>>> existing in the kernel e.g. tagged by their netns?
>>>
>>> Not at this point.  Although we have ids that are now possible of that
>>> tagging.  At this point you need to have a separate socket for each
>>> network namespace.
>> ok
>>>
>>> All network devices in all network namespaces is not going to ever
>>> happen as that makes nested containers and migration impossible.  All
>>> network devices in an interesting subset of network namespaces is a very
>>> reasonable request.
>> That would indeed be very helpful. I (and numerous other people) use
>> the Mininet network emulator (mininet.org) for research purposes. In
>> this context a centralized and efficient way to poll at least a subset
>> of namespaces would be very helpful.
>
> For reading network statistics I am not convinced that having just
> one socket instead of having several sockets provides any real world
> benefits.

We have not yet investigated the impact in detail. However, when
Mininet is used for emulating large networks, e.g. with several
thousand namespaces, I imagine that having a single socket over e.g.
1000 sockets when polling in sub second intervals could make a
difference.

>
>>>
>>>> Any pointers are appreciated :)
>>>
>>> I would look at iproute2.  Looking at the description of your code you
>> Yes, we are currently investigating the use of pyroute2, which is a
>> iproute implementation in Python.
>
> My point is specifically that in iproute2 there is ip/ipnetns.c that
> uses and in so using demonstrates how to use some of the more advanced
> features of network namespaces.

Ok, thanks for the pointer!

>
> So it is a good place to see how some of the network namespace features
> are being used.
>
>>> don't even pick up on the names that have been assigned to network
>>> namespaces.  So I don't think you are up to speed on everything that is
>>> going on there.
>> In this specific context of Mininet all required information is
>> already in the network interface name, so there is no need to get the
>> namespace name.
>
> My point was doing the equivalent of "ip netns show" could be much
> simpler and a more straighforward default than passing a sequence of
> pids.

This is a particularity of Mininet, it does not use the namespace naming at all.

>
>> Nonetheless I would like to get more up to speed, the
>> question is what is the best way to do so? There seems to be a lot of
>> information on network namespaces scattered in the man pages, the
>> Linux kernel documentation files and lwn. Is there a better place to
>> stay updated on this topic?
>
> It all depends on how much time you have to invest.  I try and keep the
> documentation up to date as I implement things but sometimes that does
> not work out.  The sources of iproute2 the kernel are always up to date
> but not necessarily the easiest to read through.

Thank you for the pointer!

Jeremias

>
> Eric
>
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