Re: Get statistics from all network interfaces on a system, including those inside network namespaces

Jeremias Blendin [off-list ref] writes:

Thank you for the detailed answer!

See also my comments below:

2015-03-20 21:10 GMT+01:00 Eric W. Biederman [off-list ref]:

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Jeremias Blendin [off-list ref] writes:

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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.

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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

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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.

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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.

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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