problem with mpd and libvirt

[Jan Palus]

On 15.12.2020 12:48, Elan Ruusamäe wrote:
> On 15.12.2020 10:51, Jan Palus wrote:
> 
> > On 14.12.2020 23:19, Krzysztof Mrozowicz wrote:
> > > Hi,
> > > I upgraded my PLD installation with today's "ready" repo and just discovered
> > > that two services I use started to segfault.
> > > 
> > > libvirtd:
> > > gru 14 23:06:34 oko libvirtd[22095]: internal error: Failed to start QEMU
> > > binary /usr/bin/qemu-system-x86_64 for probing: qemu-system-x86_64:
> > > /tmp/B.HHaAz_/BUILD/qemu-5.0.0/util/fdmon-io_uring.c:292:
> > > fdmon_io_uring_wait: Assertion `ret >= 0' failed.
> > > gru 14 23:06:34 oko libvirtd[22095]: Failed to probe capabilities for
> > > /usr/bin/qemu-system-x86_64: internal error: Failed to start QEMU binary
> > > /usr/bin/qemu-system-x86_64 for probing: qemu-system-x86_64:
> > > /tmp/B.HHaAz_/BUILD/qemu-5.0.0/util/fdmon-io_uring.c:292:
> > > fdmon_io_uring_wait: Assertion `ret >= 0' failed.
> > > 
> > > mpd:
> > > gru 14 23:16:49 oko systemd[1]: Starting Music Player Daemon...
> > > gru 14 23:16:49 oko systemd-coredump[51998]: [🡕] Process 50078 (mpd) of user
> > > 204 dumped core.
> > > 
> > > If I can do anything to help to identify the problem, please let me know.
> > mpd works fine for me but can you try upgrading mpd/qemu* to
> > versions from th-test and see if it fixes your issues?
> 
> io_uring may be related to kernel, what is your kernel, glibc, liburing,
> qemu?

It looks like ABI breakage to me -- the reason why mpd worked for me
(qemu fails the same way) is most likely due to:

* on x86_64 I'm using mpd in user session which in default configuration
  does not use io_uring (mpd requires 64M `ulimit -l` while by
  default 64K is available)

* on ARM I'm using system instance but mpd was compiled with liburing
  0.7

After quick look at liburing commits between 0.6 and 0.7 I'd say it
would be this one:

https://github.com/axboe/liburing/commit/0f0517331307605e576b3492c93dc4988e06fdc0