Date:	Sat, 21 Mar 2015 16:32:10 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jeremias Blendin <jeremias@...ndin.org>
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

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.

>>
>>> 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.

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.

> 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.

Eric

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