Re: qemu:///embed and isolation from global components

On 3/6/20 6:49 PM, Daniel P. Berrangé wrote: >> On Fri, Mar 06, 2020 at 06:24:15PM +0100, Andrea Bolognani wrote: >> Recently I've been working on integrating qemu:///embed into an >> application. It's been reasonably smooth so far :) >> >> There's one thing, however, that has caused a bit of confusion, and >> I would like to clarify whether my expectations are incorrect, there >> are genuine bugs in the implementation that need to be addressed, or >> maybe the experimental nature of embedded driver support results in >> not all scenarios having yet been considered and catered for. >> >> Using virt-qemu-run as an example, when I run it as root I see that >> >> * the domain doesn't show up in the output of 'virsh list' for >> qemu:///system; > This is good. >> * it does, however, show up in the output of 'machinectl', with >> class=vm and service=libvirt-qemu; > This is bad. It is one of the gaps we need to deal with. > A long while back I proposed a domain XML option for this: > https://www.redhat.com/archives/libvir-list/2017-December/msg00729.html > <resource register="none|direct|machined|systemd"/> > The "none" case meant inherit the cgroups placement of the parent > libvirtd (or now the app using the embedded driver), and would be > a reasonable default for the embedded case. > For the other cases, we certainly need to do something to ensure > uniqueness. This is possibly as simple as including a fixed > prefix like "qemu-$PID" where $PID is the app embedding the > driver. That said, we support closing the app, and re-starting > using the same embedded driver directory, which would change > PID. Instead of PID we can derive the value from the root path, e.g. i-node of the root dir or some substring of the path hash, say first 6 letters of md5($root_path). This would guarantee the stability of the prefix across app restarts (if we assume all root dirs to be on one FS so we don't have clashing i-node numbers).

Michal