[libvirt-users] Obtaining the PID of a domain's QEMU process from C

[Michal Privoznik]

On 3/11/19 9:02 AM, Erik Skultety wrote:
> On Sat, Mar 09, 2019 at 04:32:00PM +0100, Michal Prívozník wrote:
>> On 3/1/19 2:31 AM, Shawn Anastasio wrote:
>>> Hello all,
>>>
>>> I'm currently writing a C program that uses the libvirt API and I need a
>>> way to obtain the pid of a given domain's QEMU process.
>>>
>>> Specifically, I'm writing an ivshmem server that uses SO_PEERCRED to get
>>> the pid of clients that connect to it, and I would like to use that pid
>>> to look up the domain in libvirt to determine the proper domain ID to
>>> return to the client.
>>>
>>> As far as I can tell, libvirt doesn't expose this information in an easy
>>> to access manner. Of course it is possible to call `ps` and grep for the
>>> information I'm looking for, but I was hoping for a cleaner solution.
>>>
>>> If anybody knows how to do this, advice would be greatly appreciated.
>>
>> There isn't an API for that as we don't want users to fiddle with qemu
> 
> That's right, and it should stay that way. On the other hand, the same way we
> can't prevent anyone from editing /etc/libvirt/qemu/<domain>.xml or
> /var/run/libvirt/qemu/<domain>.xml or run the 'ps' command or whatever we might
> as well report the PID as part of virConnectListAllDomains data. I don't have
> a problem with reporting PIDs in principle, provided it's used for informatory
> purposes.
> Having said that, there's the question of why libvirt should report something
> that it doesn't need to consume, IOW we report machine ID which we can use to
> control the machine, we also report UUID which we can consume, but we'd do
> absolutely nothing with the PID besides reporting it.
> Another thing is that reporting PIDs of machines running on a remote host is
> quite useless for locally running clients.

Alternatively, we may do what LXC driver already does -> domain ID is 
PID of init running within the container. In QEMU driver, the domain ID 
can be PID of qemu then.

Michal