maybe race condition & alsa

[Francisco Lobo <lobo.f@blueyonder.co.uk>]

SALVE

After a couple of days... Success! I now have linux-2.6 + udev, and 
finally got rid of the devfs names. Thanks to everyone!

I just have ONE device node on the physical filesystem: /dev/console 
(i.e. mknod /dev/console c 5 1), because init must have it at boot. 
Then, rc.sysinit has this before any real work (fs checks):

/bin/mount -n /dev
/bin/mount -n /proc
/bin/mount -n /sys
mkdir /dev/pts
mkdir /dev/shm
/sbin/udevstart
ln -snf /proc/self/fd /dev/fd
ln -snf /proc/self/fd/0 /dev/stdin
ln -snf /proc/self/fd/1 /dev/stdout
ln -snf /proc/self/fd/2 /dev/stderr
ln -snf /proc/kcore /dev/core

PRONTO!

Maybe the documentation for udev should hint that /dev/console is the 
only device needed to boot (or maybe I didn't read it well).

Getting alsa to work was a very different story! Although this problem 
might just be alsa related (alsactl in particular), I though the 
following info should help people migrate to udev, so:

1. with udev the following modprobe.conf lines are not working for me

install snd-card-0 /sbin/modprobe --ignore-install snd-card-0 && \
	{ /usr/sbin/alsactl restore >/dev/null 2>&1 || :; }
remove snd-card-0 { /usr/sbin/alsactl store >/dev/null 2>&1 || :; } ; \
	/sbin/modprobe -r --ignore-remove snd-card-0

2. although there are no error messages, the fact is the alsactl cannot
find the sound card (/dev entries), so when one tries to play something 
the sound is mute

The solution I found is:

1. replace hotplug init script with:

echo "/sbin/udev" > /proc/sys/kernel/hotplug

2. immediately after that load the snd-card-0 and other module(s) in a 
modules init script

3. then in a later init script do the alsactl part, and by "later" I 
mean after a few other ones, or else same problem as above - you might 
use some adequate sleep value before alsactl command (but?)

What I mean by a possible race condition is that alsactl will not find 
the /dev entries if this procedure is not exactly followed. Also, this 
will ONLY work with udev as the hotplug program! The hotplug scripts are 
simply too slow to respond (I've tried sleep 2 before alsactl and 
nothing, at least with hotplug-2004_01_05 - NOTE: I don't have 
pcimodules, yet hotplug should use sysfs shouldn't it?)

Of course, alsactl could/should do more to find the sound card... I did 
not check its sources to see how this is done... But it seems plausible 
that it is only doing a stat on /dev entries, and maybe it could ask the 
kernel for sound devices, which might then make the modprobe / udev / 
hotplug processes to finish whatever they have to do. (I don't know much 
about this, it just feels that something like it could sort things out.)

The obvious problem with this solution is that one always has the sound 
modules, even if we're not going to jam!

Salu!

Francisco.


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