By the way, there is a typo in the commit title ("vitual").

@ivy Makefile.inc defines:

PACKAGE?=	sound

Is it a problem if the inclusion is removed from here?

Neither lib/virtual_oss nor usr.sbin/virtual_oss build with this patch:

root@freebsd:/mnt/src/lib/virtual_oss # make
Building /usr/obj/mnt/src/amd64.amd64/lib/virtual_oss/null/null.pico
In file included from /mnt/src/lib/virtual_oss/null/null.c:39:
/mnt/src/usr.sbin/virtual_oss/virtual_oss/int.h:33:10: fatal error: 'samplerate.h' file not found
   33 | #include <samplerate.h>

In D54456#1248939, @zarychtam_plan-b.pwste.edu.pl wrote:

Congratulations and thanks for this great solution! It's now 100% compatible with the "WITHOUT_MODULES sound" kernel build and install knob and covers the entire sound toolkit.

@zarychtam_plan-b.pwste.edu.pl @rozhuk.im-gmail.com Opinions?

Should this be committed now?

In D54360#1244384, @meka_tilda.center wrote:

In D54360#1244383, @christos wrote:

The USB stack seems to have a default kqfilter method,so I suppose this is why it works. Does it work properly though?

Almost perfectly in my testing. Problem is that kevent.data is always 0 and as kqueue is advertised as "after the fact" eventing system, it would be nice to get the event after all 3 bytes are ready. I'm speaking strictly about notes and controllers, but similar is true for any MIDI message: I'd like to receive event once the whole message is ready. In this code you'll notice I read 2 more bytes after initial read. That feels like magic, so it would be nice to get event.data = 3 and read the whole MIDI message at once.

Replace MK_VOSS with MK_SOUND after discussion with Mark.

For testing you can use snd_dummy(4), I added some basic MIDI support, although you might need to make it more functional because it basically does more or less nothing currently.