[9fans] usb audio

[rog@vitanuova.com]

i just got my new xitel hifi-link (on presotto's recommendation), and
hacked madplay so that it sets the speed and number of channels
appropriately to the mp3 file.

only problem is that doing this when the /dev/audio is already open
reliably crashes the kernel.
(first i get a write error from usbaudio:
	writing ep 4 1 w 4 44100 to #U/usb0/1/ctl: permission denied,
then the kernel panics with "fault: xxx")

i've now fixed it so it closes /dev/audio before writing to audioctl
and then reopens it, but it doesn't seem like this should be
necessary.

the other thing is i'd really like usbaudio to attach to the correct
usb port automatically: is there enough information provided by the
usb device to automatically identify an audio device (currently i look
at the output of usbd -v, or have a look in /dev/usb0)?

those issues aside, it works very nicely, thanks...  i can finally
play mp3 files. (mind you, i've only got two so far!)

i guess the next step is a little audio plumbing client that knows how
to stop one stream and start another when a new plumbing request comes
in; then the world is my jukebox.