[Qemu-devel] [Bug 1816052] Re: qemu system emulator fails to start if no sound card is present on host

[Kris M <krislema2@gmail.com>]

That was Ubuntu DD current on comment #1

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

Status in QEMU:
  New

Bug description:
  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 <kraxel@redhat.com>
    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 <kraxel@redhat.com>
      Message-id: 20190124112055.547-7-kraxel@redhat.com

  
  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.

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