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

[Aivils <ai...@un...>]

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.

Aivils