/dev/sequencer descriptions

/dev/sequencer descriptions

[Andrey Konovalov]

Hi Takashi,

We're working on syzkaller descriptions for /dev/sequencer [1], but
have some troubles understanding its functionality. The main question
is: is sound/synth/emux/ code reachable when tested in a VM (we're
using QEMU with -soundhw all), or does it require some specific
hardware to be present?

In our setup (with Debian Stretch userspace image) we have
/dev/sequencer with SNDRV_MINOR_OSS_SEQUENCER and /dev/sequencer2 with
SNDRV_MINOR_OSS_MUSIC. For the former, there are no synth devices as
reported by SNDCTL_SEQ_NRSYNTHS. For the latter, synth devices are
there, but the load_patch() callback is not reachable as this check
[2] fails.

Is that code impossible to test in a VM at all? Or are there some
specific kernel options/drivers that need to be enabled?

Thanks!

[1] https://github.com/google/syzkaller/pull/1952

[2] https://elixir.bootlin.com/linux/v5.7.8/source/sound/core/seq/oss/seq_oss_synth.c#L452

Re: /dev/sequencer descriptions

[Takashi Iwai]

On Mon, 27 Jul 2020 19:47:54 +0200,
Andrey Konovalov wrote:
> 
> Hi Takashi,
> 
> We're working on syzkaller descriptions for /dev/sequencer [1], but
> have some troubles understanding its functionality. The main question
> is: is sound/synth/emux/ code reachable when tested in a VM (we're
> using QEMU with -soundhw all), or does it require some specific
> hardware to be present?

It's for Creative SoundBlaster EMU chips, and it needs the specific
hardware that isn't emulated, so far.

> In our setup (with Debian Stretch userspace image) we have
> /dev/sequencer with SNDRV_MINOR_OSS_SEQUENCER and /dev/sequencer2 with
> SNDRV_MINOR_OSS_MUSIC. For the former, there are no synth devices as
> reported by SNDCTL_SEQ_NRSYNTHS. For the latter, synth devices are
> there, but the load_patch() callback is not reachable as this check
> [2] fails.
> 
> Is that code impossible to test in a VM at all? Or are there some
> specific kernel options/drivers that need to be enabled?

Another possible device supporting the OSS sequencer is the old FM
OPL3.  But it seems also not properly implemented in QEMU (I see only
OPL2), unfortunately.


thanks,

Takashi

Re: /dev/sequencer descriptions

[Andrey Konovalov]

On Mon, Jul 27, 2020 at 8:02 PM Takashi Iwai <tiwai@suse.de> wrote:
>
> On Mon, 27 Jul 2020 19:47:54 +0200,
> Andrey Konovalov wrote:
> >
> > Hi Takashi,
> >
> > We're working on syzkaller descriptions for /dev/sequencer [1], but
> > have some troubles understanding its functionality. The main question
> > is: is sound/synth/emux/ code reachable when tested in a VM (we're
> > using QEMU with -soundhw all), or does it require some specific
> > hardware to be present?
>
> It's for Creative SoundBlaster EMU chips, and it needs the specific
> hardware that isn't emulated, so far.
>
> > In our setup (with Debian Stretch userspace image) we have
> > /dev/sequencer with SNDRV_MINOR_OSS_SEQUENCER and /dev/sequencer2 with
> > SNDRV_MINOR_OSS_MUSIC. For the former, there are no synth devices as
> > reported by SNDCTL_SEQ_NRSYNTHS. For the latter, synth devices are
> > there, but the load_patch() callback is not reachable as this check
> > [2] fails.
> >
> > Is that code impossible to test in a VM at all? Or are there some
> > specific kernel options/drivers that need to be enabled?
>
> Another possible device supporting the OSS sequencer is the old FM
> OPL3.  But it seems also not properly implemented in QEMU (I see only
> OPL2), unfortunately.

OK, got it, thank you!