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

[Shawn Anastasio]

Thanks for the response. /var/run/libvirt/qemu/ seems to be exactly what 
I'm looking for. It would, however, be nice to be able to access this 
file without root privileges. Is there any way to access the file using 
the credentials from a connected virConnectPtr?

If not, I can stick to my current workaround of walking /proc and 
scanning each PID's cmdline for the VM's UUID string.

Thanks,
Shawn

On 3/9/19 9:32 AM, 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
> behid its back. Anyway, apart from ps there might be a solution. Libvirt
> of course know the PID and stores it - in the status XML. This is a file
> that libvirt uses to store runtime information for the domain in case
> the daemon restarts. It's located under
> /var/run/libvirt/qemu/$domain.xml. But you'll need root priviledges to
> read it.
> 
> Also, it is very wise to follow the comment at the beginning of the file
> and not modify it ;-) And just like with any libvirt internals, we make
> no guarantees they won't change in the long run.
> 
> Michal
>