list of all network namespaces

list of all network namespaces

[Ani Sinha]

Hi guys

just a stupid question. Is it possible to get a list of all active
network namespaces in the kernel through /proc or some other
interface?

thanks
ani

Re: list of all network namespaces

[Rick Jones]

On 09/16/2015 05:46 PM, Ani Sinha wrote:
> Hi guys
>
> just a stupid question. Is it possible to get a list of all active
> network namespaces in the kernel through /proc or some other
> interface?

Presumably you could copy what "ip netns" does, which appears to be to 
look in /var/run/netns .  At least that is what an strace of that 
command suggests.

rick jones

Re: list of all network namespaces

[Jiri Benc]

On Wed, 16 Sep 2015 17:54:34 -0700, Rick Jones wrote:
> On 09/16/2015 05:46 PM, Ani Sinha wrote:
> > just a stupid question. Is it possible to get a list of all active
> > network namespaces in the kernel through /proc or some other
> > interface?

Not reliably and not efficiently. You can look at what plotnetcfg does:
https://github.com/jbenc/plotnetcfg/blob/master/netns.c

> Presumably you could copy what "ip netns" does, which appears to be to 
> look in /var/run/netns .  At least that is what an strace of that 
> command suggests.

That only works for namespaces added by the ip tool (and presumably a
few other tools which leave a symlink in /var/run/netns as a courtesy).
Depending on what you need, it may be enough. Be aware that you won't
find all net namespaces in the system this way, though.

 Jiri

-- 
Jiri Benc

Re: list of all network namespaces

[Nicolas Dichtel]

Le 17/09/2015 02:54, Rick Jones a écrit :
> On 09/16/2015 05:46 PM, Ani Sinha wrote:
>> Hi guys
>>
>> just a stupid question. Is it possible to get a list of all active
>> network namespaces in the kernel through /proc or some other
>> interface?
>
> Presumably you could copy what "ip netns" does, which appears to be to look in
> /var/run/netns .  At least that is what an strace of that command suggests.
This will only list netns referenced in '/var/run/netns', which is not 'all'
existing netns (most probably only netns created by iproute2).

Regards,
Nicolas

RE: list of all network namespaces

[Rosen, Rami]

Hi,

>Presumably you could copy what "ip netns" does, which appears to be to look in /var/run/netns .  At least that is what an strace of that >command suggests.

This is true, but keep in mind that the output of "ip netns", as well as listing the contents of /var/run/netns, reflects only network namespaces
which were created with the "ip netns" command. The "ip netns" userspace implementation consists of code which enables this,
by creating /var/run/netns, bind mounting it, etc.

Network namespaces which were created by other ways (like userspace applications
using the clone() system call) will *not* be reflected by neither of them.

Regards,
Rami Rosen
Intel Corporation

Re: list of all network namespaces

[Ani Sinha]

On Thu, Sep 17, 2015 at 2:51 AM, Rosen, Rami <rami.rosen@intel.com> wrote:

> Network namespaces which were created by other ways (like userspace applications
> using the clone() system call) will *not* be reflected by neither of them.

Will there be any interest if I cook up a kernel patch that lists all
network namespaces through /proc?

Re: list of all network namespaces

[Cong Wang]

On Thu, Sep 17, 2015 at 10:39 AM, Ani Sinha <ani@arista.com> wrote:
> On Thu, Sep 17, 2015 at 2:51 AM, Rosen, Rami <rami.rosen@intel.com> wrote:
>
>> Network namespaces which were created by other ways (like userspace applications
>> using the clone() system call) will *not* be reflected by neither of them.
>
> Will there be any interest if I cook up a kernel patch that lists all
> network namespaces through /proc?

How do you list them since they don't have names in kernel, names
are given in user-space.

Re: list of all network namespaces

[Jiri Benc]

On Thu, 17 Sep 2015 10:39:57 -0700, Ani Sinha wrote:
> Will there be any interest if I cook up a kernel patch that lists all
> network namespaces through /proc?

/proc is a wrong interface for this, enumerating all net namespaces has
nothing to do with processes. Each process has its corresponding
namespaces in /proc already listed, which is as much as belongs
to /proc.

Dumping all net namespaces should be probably netlink based but
obviously, you'll have hard time sending file descriptors over netlink.
You can dump their netnsids but that won't help you much accessing the
namespace contents.

This is not as easy as it seems. But I'd love to have such feature.

 Jiri

-- 
Jiri Benc