Shawn Anastasio
2019-Mar-09 17:26 UTC
Re: [libvirt-users] Obtaining the PID of a domain's QEMU process from C
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 >
Peter Crowther
2019-Mar-09 19:14 UTC
Re: [libvirt-users] Obtaining the PID of a domain's QEMU process from C
On Sat, 9 Mar 2019 at 17:27, Shawn Anastasio <shawn@anastas.io> wrote:> 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. >Use a tiny setuid C program that reads the relevant file and writes it to a known UNIX-domain socket that has more liberal permissions? On past experience, I wouldn't expect this to end up being supported in libvirt, though there's nothing to stop you creating your own patched version. Cheers, - Peter
Shawn Anastasio
2019-Mar-09 20:32 UTC
Re: [libvirt-users] Obtaining the PID of a domain's QEMU process from C
On 3/9/19 1:14 PM, Peter Crowther wrote:> Use a tiny setuid C program that reads the relevant file and writes it to a > known UNIX-domain socket that has more liberal permissions?Indeed this is a possibility, but I was hoping for a cleaner solution that fit in with libvirt's existing authentication mechanisms. > I wouldn't expect this to end up being supported in libvirt, > though there's nothing to stop you creating your own patched version. That's a shame, but it's certainly not the end of the world. I may end up running my daemon as root, forking before dropping privileges, and using the child to open the files and pass them to the parent using SCM_RIGHTS or something. Thanks, Shawn
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