sound: Move pcm_chnref() and pcm_chnrelease() to pcm/channel.c

[christos]

Summary

Improve code layering. These are channel functions, and so they do not
belong in pcm/sound.c.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week

[markj]

sys/dev/sound/pcm/channel.c

1338

Since ref can be negative, it would be nice to assert against underflow while you're here. i.e., if ref < 0, then we'd better have c->refcount >= -ref.

[christos]

sys/dev/sound/pcm/channel.c

1338

Wouldn't it be better to just assert than c->refcount >= 0?

[markj]

sys/dev/sound/pcm/channel.c

1338

It's generally better to assert before performing the operation, but yes that works too.

[christos]

sys/dev/sound/pcm/channel.c

1338

Actually I think what we need to do is check if c->refcount + ref >= 0, not c->refcount >= 0:

	KASSERT((c->refcount + ref) >= 0,
	    ("%s(): new refcount will be negative", __func__));

[markj]

sys/dev/sound/pcm/channel.c

1338

Seems ok to me.