Le 9 mars 2020 à 14:03, Michal Privoznik <mprivozn@redhat.com> a écrit :
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).
Root path hash is more robust also in other cases, like file copy/rename often used for atomic updates.
Michal