sound: Get rid of pnum and max variables in chn_init()

[christos]

Summary

The VCHAN count is checked in vchan_setnew(), and there is no reason to
cap the hardware channels in the first place.

This is part of a series of follow-up patches.

Sponsored by: The FreeBSD Foundation
MFC after: 2 days

[dev_submerge.ch]

sys/dev/sound/pcm/channel.c

1205

Not related to this patch, but to the overall topic of vchan_setnew(): I suppose the unit number should be unique, right? Are we sure this is the case when somebody lowers the vchan sysctls and vchan_setnew() garbage collects some of the intermediate vchans?

[christos]

sys/dev/sound/pcm/channel.c

1205

If I understand correctly, what you are asking is the following. Suppose we have the following state:

vp0 -> unused
vp1 -> unused
vp2 -> someapp

If we lower the VCHAN amount to 1, we'll get the following:

vp2 -> someapp

Then, we set them to 4, and spawn 3 VCHANs:

vp0 -> foo
vp1 -> bar
vp2 -> someapp?
vp3 -> baz?

Apparently, after some testing now, I found out that in this scenario we'll override vp2 and essentially break things. Currently chn_init() does not make sure the unit doesn't already exist and instead just picks the length of the channel list (for a given direction) as the new unit number, which, as demonstrated in this example, can result in picking a unit number that already exists, when creating the 3rd channel.

What we should be doing in this loop is checking that c->unit != unit.

[dev_submerge.ch]

sys/dev/sound/pcm/channel.c

1205

Bingo! ;-)
Didn't have time to test it yesterday before I had to leave.

[christos]

Any comment related to the patch?

sys/dev/sound/pcm/channel.c

1205

I will fix this ASAP, as it currently hangs sound(4). I think we end up in some infinite loop in either vchan_setnew() or something. Will have to investigate...

[christos]

sys/dev/sound/pcm/channel.c

1205

@dev_submerge.ch D46548 fixes the actual hang (although, as mentioned in the commit message) I am not completely sure which part exactly caused it, and D46550 fixes the unique unit problem. D46549 is needed in order to simplify the unit assignment (easier to work with a sorted list).