Re: Assigning sound card to specific X display - the chroot+bind-mount way

[Helge H. <hel...@ai...>]

Aivils wrote:

>On Friday 03 June 2005 12:03, Helge Hafting wrote:
>  
>
>>Aivils wrote:
>>
>>    
>>
>>>On Thursday 02 June 2005 04:27, Ken McCord wrote:
>>> 
>>>
>>>      
>>>
>>>>I'm running a dual-head setup using Debian unstable + the x.org packages
>>>>        
>>>>
>>>>from Ubuntu.  I have two sound cards, and I'd like to assign each of
>>>      
>>>
>>>>them
>>>>to a specific X display.  How can I do this?
>>>>
>>>>The first sound card is /dev/dsp and the second is /dev/dsp1.  I want
>>>>display :0 to use /dev/dsp and display :1 to use /dev/dsp1.
>>>>
>>>>I've tried the instructions available at
>>>>http://howtos.linux.com/howtos/XFree-Local-multi-user-HOWTO/automation_multy_snd-cards.shtml
>>>>but I haven't been able to get them to work with gdm/Gnome.
>>>>   
>>>>
>>>>        
>>>>
>>>Under Linux access to sound subsystem  is little chaotic.
>>>Any application use hers own sound driver.
>>>
>>>Try out set up artsd under KDE or esd under GNOME . 
>>>
>>>Even if these software sound mixers like artsd or esd runs
>>>properly, then You cannot disable Java and Flash Player,
>>>which uses sound device directly.
>>>I open Java binary with hexedit and manulay replace
>>>/dev/dsp with fake non-existing device file for silence.
>>> 
>>>
>>>      
>>>
>>There is a way.
>>One xserver can run in its own chroot.  The two servers can have
>>distinct /dev directories that way, where the two "dsp" files in the
>>distinct directories have different device numbers and so
>>refer to different sound devices.
>>Make a copy of /dev in /chroot/dev.  In there, make sure
>>"dsp" refers to the second soundcard instead of the first.
>>
>>On a debian system "dsp" is a symlink to "dsp0".  Change it to
>>a link to "dsp1" instead.  On other systems you may have to
>>do something like "mv dsp1 dsp0".
>>
>>Whatever the solution is, do the same for all other sound-related
>>files, such as "mixer" and so on.
>>
>>
>>Now the chroot has a customized /dev.  But what about all the
>>other directories needed for normal operation, such as
>>/bin, /usr, /var, /home and so on?
>>
>>The answer is to bind-mount them.  Bind-mount every top-level
>>directory except /dev into the chroot, and you should be fine.
>>Then chroot into the /chroot directory, and start the second xserver.
>>(Details: man mount, search for "bind")
>>
>>Having all those bind-mounts means you don't have to duplicate
>>a single file (except for the contents of /dev).  Both xservers will
>>access the same files, so they should work and the users shouldn't
>>be able to notice the difference. Except that they get distinct soundcards.
>>
>>I use a different approach at home.  The machine happens to have
>>two soundcards, but I use only one of them currently.  It has a trident
>>chip, and that one support multiple users at the same time so no
>>problems there.  The two displays are side by side with the speakers
>>on each side of both of them, so both get correct stereo sound from the
>>same speaker set.
>>    
>>
>
>Masterpiece must be an intelligent script for each /dev/input/eventXX
>/dev/input/mouseXX /dev/sound/dspXX , where devices allways are links to 
>/chroot/XX/dev/input/mouse0 and so on. In case of input devices,
>device files changed on unplug/plug in.
>  
>
There should be no problems with input devices.  Each xserver
can trivially have a different config file, specifying the correct mouse.

It is only the sound devices that need to be different, and only because
it is "too hard" getting every sound-using program to use the correct
device.

If someone actually have a setup where the contents of /dev/input/
_change_ over time, well, just make bind-mount /dev/input over
/chroot/dev/input in order to see the same input devices everywhere.
Sound devices aren't in /dev/input and can still be different.

Helge Hafting