qemu system emulator fails to start if no sound card is present on host

[Daniel Berrange]

A plain build from git master at 81dbcfa9e1d8bab3f7c4cc923c0b40cd666f374f on Fedora 29 x86_64 host, with no options passed to configure.

Trying to launch QEMU on a host with no audio card present:

# ls /dev/snd/
seq timer

It will fail to initialize alsa and abort startup:

# qemu-system-x86_64 -cdrom Fedora-Workstation-Live-x86_64-29-1.2.iso -m 4000 -vnc 0.0.0.0:1
ALSA lib confmisc.c:767:(parse_card) cannot find card '0'
ALSA lib conf.c:4555:(_snd_config_evaluate) function snd_func_card_driver returned error: No such file or directory
ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
ALSA lib conf.c:4555:(_snd_config_evaluate) function snd_func_concat returned error: No such file or directory
ALSA lib confmisc.c:1246:(snd_func_refer) error evaluating name
ALSA lib conf.c:4555:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5034:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2565:(snd_pcm_open_noupdate) Unknown PCM default
alsa: Could not initialize DAC
alsa: Failed to open `default':
alsa: Reason: No such file or directory
ALSA lib confmisc.c:767:(parse_card) cannot find card '0'
ALSA lib conf.c:4555:(_snd_config_evaluate) function snd_func_card_driver returned error: No such file or directory
ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
ALSA lib conf.c:4555:(_snd_config_evaluate) function snd_func_concat returned error: No such file or directory
ALSA lib confmisc.c:1246:(snd_func_refer) error evaluating name
ALSA lib conf.c:4555:(_snd_config_evaluate) function snd_func_refer returned error: No such file or directory
ALSA lib conf.c:5034:(snd_config_expand) Evaluate error: No such file or directory
ALSA lib pcm.c:2565:(snd_pcm_open_noupdate) Unknown PCM default
alsa: Could not initialize DAC
alsa: Failed to open `default':
alsa: Reason: No such file or directory
init fail
audio: Failed to create voice `pcspk'
qemu-system-x86_64: Initialization of device isa-pcspk failed: Initializing audio voice failed

git bisect blames this change:

  commit 6a48541873f14b597630283f8f5397674ad82ea9 (HEAD, refs/bisect/bad)
  Author: Gerd Hoffmann <email address hidden>
  Date: Thu Jan 24 12:20:55 2019 +0100

    audio: probe audio drivers by default

    Add the drivers listed in audio_possible_drivers to audio_drv_list,
    using the try-* variants. That way the probable drivers are compiled by
    default if possible.

    Additioal tweaks:
      linux: reorder to: pa alsa sdl oss.
      *bsd: drop pa.

    Signed-off-by: Gerd Hoffmann <email address hidden>
    Message-id: <email address hidden>

This changed our probe order:

   Linux)
  - audio_drv_list="oss"
  + audio_drv_list="try-pa try-alsa try-sdl oss"

After some debugging I can see that 'audio_init' successfully initializes the alsa driver.

When the pcspk devices goes to AUD_open_out though, the alsa driver fails spewing the above text to stderr and thus causes QEMU to fail.

This looks very much like the ALSA driver in QEMU is broken - audio_init() should not have succeeded unless the ALSA driver knew it could later succesfully honour AUD_open_out.

[Kris M (krislema2)]

Don't know if same but just noticed "no sound" unless I unplug and replug headphones. If I boot with no headphones plugged in I get no sound, but if I plug in headphones I get sound. Of course, then, if I unplug headphones I still get sound. Something about plugging/unplugging to the headphones jack wakes things up.

ThinkPad T530-2394-3J8, i5-3380M 2.9GHz, Dual boot (BIOS/MBR): Grub, Ubuntu 18.10 / Win7 Pro x64 . 8GB(15GB/s), Sammy 250GB SSD. Fast!

4.19.0-13 kern and previous. current: I take all updates.

[Kris M (krislema2)]

That was Ubuntu DD current on comment #1

[Jeremy Bícha (jbicha)]

Kris, your situation is completely different.

[Kris M (krislema2)]

I agree. Thanks. :)

[Gerd Hoffmann (kraxel-redhat)]

What happens if you remove "try-alsa" from the configure line?

[Like Xu (likexu)]

I would work around this issue
by applying "export QEMU_AUDIO_DRV=none" to shell before we run the qemu command.

[Peter Maydell (pmaydell)]

This bug was fixed by commit 7183834a29fbaf422a6 which will be in 4.0.