using libvirt 4.5 with upstream qemu

[Thanos Makatos]

> -----Original Message-----
> From: Daniel Henrique Barboza <danielhb413 at gmail.com>
> Sent: 01 March 2021 18:07
> To: Peter Krempa <pkrempa at redhat.com>; Thanos Makatos
> <thanos.makatos at nutanix.com>
> Cc: libvir-list at 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.

Thanks Daniel, removing --enable-trace-backend did fix the issue!