RE: using libvirt 4.5 with upstream qemu

-----Original Message----- From: Daniel Henrique Barboza <danielhb413(a)gmail.com&gt; Sent: 01 March 2021 18:07 To: Peter Krempa <pkrempa(a)redhat.com>; Thanos Makatos <thanos.makatos(a)nutanix.com&gt; Cc: libvir-list(a)redhat.com Subject: Re: using libvirt 4.5 with upstream qemu On 3/1/21 12:47 PM, Peter Krempa wrote: > 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. Not sure if related to this reported problem, but upstream QEMU when compiled with the trace backend was having problems daemonizing. I experienced a similar issue in the start of the year when running upstream Libvirt with upstream QEMU. I posted a patch fixing it in QEMU [1] but it wasn't pushed as of today. I am not sure if the problem was fixed in another way or if the patch I posted ended up left behind. Thanos, if you're compiling QEMU with a trace backend (e.g. with --enable- trace-backend= in ../configure) it might be worth compiling it without this option. There is a chance you're hitting same problem I mentioned above.