On Mon, Mar 01, 2021 at 15:30:58 +0000, Thanos Makatos wrote: > I'm trying to use QEMU master with libvirt 4.5 and QEMU seems to be hanging > when I try to start a guest. > > My environment is a modified CentOS 7.9 installation using libvirt 4.5.0. When > I use a modified version of QEMU 2.12 (reasonably close to the stock CentOS > version) everything works fine. When I try to use a fairly recent version of > QEMU (e.g. v5.2.0-729-g89ff714f4b). > > qemu 118657 1.6 0.0 0 0 ? Z 14:50 0:00 [qemu-kvm] <defunct> > qemu 118664 0.0 0.0 207340 3560 ? Ssl 14:50 0:00 /usr/libexec/qemu-kvm -S -no-user-config -nodefaults -nographic -machine none,accel=kvm:tcg -qmp unix:/var/lib/libvirt/qemu/capabilities.monitor.sock,server,nowait -pidfile /var/lib/libvirt/qemu/capabilities.pidfile -daemonize > qemu 118666 0.0 0.0 275008 13916 ? Sl 14:50 0:00 /usr/libexec/qemu-kvm -S -no-user-config -nodefaults -nographic -machine none,accel=kvm:tcg -qmp unix:/var/lib/libvirt/qemu/capabilities.monitor.sock,server,nowait -pidfile /var/lib/libvirt/qemu/capabilities.pidfile -daemonize These are possibly a leftover from libvirt's capability probing. I recall that we had some issue with capability detection qemu instances getting stuck but I don't remember the details any more. > /var/lib/libvirt/qemu/capabilities.pidfile contains the PID of the 2nd QEMU > process and by experimenting I found that by killing the QEMU process NOT in > the PID file the same thing happens again (maybe once more or twice) and then > the guest boots fine. > > Does libvirt have some specific QEMU dependency? Is there some compatibility > matrix I might have missed? I understand this may not be a supported > configuration given that I'm not using vanilla libvirt/QEMU, however I'd > appreciate some pointers so I can further debug this. I've trying debugging > this in case there's some obvious error but didn't find anything interesting. > > Any ideas? In general, libvirt can't guarantee support of future qemu versions as qemu evolving and recently also deprecating and removing superseded configuration approaches, so you must cross-check with qemu's support policy. For debugging, debug logs may be helpful. In case a real VM getting stuck also the VM log file, but in your case the capability processes don't have that.
