[libvirt] What is the robust/recommended way to retrieve the PID of a VM's init process ?

[Daniel P. Berrange]

On Mon, Jan 20, 2014 at 11:38:08AM +0100, Thierry Parmentelat wrote:
> Hello there
> 
> I am trying to locate the namespaces in place for a given lxc container (specifically /proc/<pid>/ns/*)
> 
> And to this end I was wondering what is the recommended way to probe for an lxc container's init pid
> (mostly I'm after the mnt and pid namespaces, and probably network ones, but the actual list probably should not matter) 
> 
> I've found about "virsh domid" but this gives me the pid for libvirt_lxc, which turns out to have unmodified namespaces (at least as far as the mnt ns)
> OTOH this process has exactly one child which is the container's init, which seems to have the right set of namespaces 
> 
> My angle right now is to look in /proc/<domid_pid>/task/children for a - hopefully single - pid and
> that seems to work for now, but I am concerned this code may be fragile so I would rather use a more
> robust approach; or maybe this is robust ? 

We don't really wish to expose the container PIDs to the host or namespace
details to client apps. Can you give more info about what you're trying to
achieve overall. I'd like to understand if there's some higher level API
we're missing that would more directly address your needs.


Daniel
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