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_sy...