[alsa-devel] my udev rules are breaking my dmixer setup why?

[Jelle de Jong]

Jaroslav Kysela wrote:
> On Tue, 11 Nov 2008, Takashi Iwai wrote:
> 
>>> Almost all devices can be managed with udev rules, that is where the
>>> system is designed for, there are also alsa rules in there, if they
>>> don't work what is wrong then? is it an alsa issue, or udev, what are
>>> the dependencies when alsa uses hardware. How are the /dev/snd/* devices
>>> used and what is the /proc/asound/* for ?
>> The card index mechanism in ALSA was introduced much before udev
>> was born.  It's just a legacy mechanism, but it's hard to kill without
>> breaking the running system, unfortunately.
> 
> Note that you can identify your card via the text identification (check 
> /proc/asound/cards to get it in []). You can set this identification in 
> the module insert time and use for example 'hw:Intel' in your apps without 
> bothering with indexes.
> 
> The missing part is the modification of this text identification using
> sysfs at runtime for udev. Some time ago, I was trying to add this setup 
> to /sys/class/sound, but the sysfs core code was not prepared for this 
> change. I'll try to check the situation again.
> 

As response to:
http://mailman.alsa-project.org/pipermail/alsa-devel/2008-November/012366.html

I am not sure if it is good practice to repose to an RFC if so please
tell me then we will continue the discussion in the RFC thread.

Thank you Jaroslav for creating the patch this is really appreciated, if
all things work I will send you some dutch stroopwafels :-D

I am just curious how you patch can be used with udev? What did you have
in mind?

Would something like this be possible:

SUBSYSTEM=="sound", ACTION="add" KERNELS=="3-1",
NAME="snd/by-id/audiodevice0"
SUBSYSTEM=="sound", ACTION="add" KERNELS=="3-2",
NAME="snd/by-id/audiodevice1"

pcm.!default {
   type plug
   slave.pcm dmixer
}
pcm.dmixer {
   type dmix
   ipc_key 1024
   slave.pcm hw:audiodevice0
}
ctl.dmixer {
   type hw
   card audiodevice0
}
pcm.dsp {
    type plug
    slave.pcm dmixer
}
ctl.mixer {
    type hw
    card audiodevice0
}

Thanks in advance,

Jelle