linux-kernel - snd/core, freeing the device driver when an USB audio device is unplugged

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Date:	Tue, 2 Jan 2007 21:53:23 -0500
From:	"Jon Smirl" <jonsmirl@...il.com>
To:	alsa-devel@...a-project.org, lkml <linux-kernel@...r.kernel.org>
Subject: snd/core, freeing the device driver when an USB audio device is unplugged

There is a basic problem in the way snd/core is handling the removal
of devices. If I unplug a USB audio device snd/core will end up in:
snd_card_free_when_closed. This isn't good because some desktop app
(don't know which one) keeps the sound device open until it exits.
This is not a good state to be in, the hardware is gone but the device
is still around.

Now if I plug the USB audio device back in, I get a sysfs error for
registering duplicate devices. Because snd_card_free_when_closed. is
waiting for the old device to be closed it is never freeing the sysfs
device. More looks to be messed up inside of snd/core when in this
state, but this is the obvious symptom.

Things do work properly if I restart gnome (killing whoever has the
card open) after I unplug the device and before I plug it back in
again.

I added a few printk to snd/core/init.c

-- I unplug my USB sound device
usb 2-1: USB disconnect, address 2
-- Inside sound core, I go into snd_card_free_when_closed
snd_card_free_when_closed

-- If I plug the snd device back in , the kernel will complain about a
device being registered twice. That because gnome (or something in the
desktop) is still holding the device open.

--- Now I restart gnome which closes whatever had the card open
snd_card_file_remove
snd_card_do_free
-- device finishes getting unregistered
unregistering device

using 2.6.20-rc3

-- 
Jon Smirl
jonsmirl@...il.com
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