On 04/09/2015 06:32 PM, Troy Engel wrote:
On Thu, Apr 9, 2015 at 7:28 PM, Steven Grace <sgrace@xxxxxxxxx> wrote:
All I'm trying to find out is how to diagnose this module problem further. I
know that module snd_seq_midi is part of the "linux" package but I don't
know what process used to add the module automatically; was it the Linux
kernel, or ALSA, or something else? I think the change is a regression and
I'd like it to be fixed but I don't know what package is responsible and
would like to know how to find out. Thanks.
In general - when the hardware scan is triggered on boot (second
phase, not initramfs) it probes your hardware and looks for modules
that deal with the device. The udev subsytem is basically a fancy
ruleset on the messagebus - it listens for events and performs actions
in /dev. (this is grossly oversimplified, just work with me here :) )
It's the 2.6+ successor to hotplug and devfs.
Your system should be booting and finding a sound card; this triggers
the subsystem "sound" to load, which in turn triggers udev; take a
look in /usr/lib/udev/rules.d/50-udev-default.rules and you'll find
this stanza:
SUBSYSTEM=="sound", GROUP="audio", \
OPTIONS+="static_node=snd/seq", OPTIONS+="static_node=snd/timer"
A double-equals means compare, a single means assign (so it's not all
loose like bash, there is a strict interpretation) and as expected +=
means add to. So when sound is detected, the udev tree should create
two device nodes -- /dev/snd/seq and /dev/snd/timer with group
'audio'. Does this happen on your machine, are you getting
/dev/snd/seq created from a fresh boot?
If you are, then that means the problem feels like it's in the seq
subsystem[1] -- when that node is created the core module (snd-seq)
should load as it's hooked into it and "see" your midi sequencer out
of this new device node and do the needful; but if you're not getting
this device node created, then it feels like the sound system isn't
triggering in udev correctly. You could of course correct the failure
with a simple .conf file over in /etc/modprobe.d/ but you're clearly
interested in determining the actual root cause.
Hope this helps! I know little about the sound subsystem (I push play,
I get music :) ), but deal with udev for storage and network devices
quite a bit. You may find it valuable to read this article, IMHO it's
quite a good writeup:
http://www.linux.com/news/hardware/peripherals/180950-udev
-te
[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/sound/core/seq
Thank you very much for this information. I confirmed that my
50-udev-default.rules file contains the stanza you listed and that the
two device nodes are being created.
If I'm understanding you correctly the Linux kernel is responsible for
loading module snd_seq_midi and is apparently no longer doing that.
I didn't mention this previously but I'm not the only one experiencing
this issue. I first posted at the LinuxMusicians forum and a user there
who uses Arch had the same issue and used the same workaround of
manually loading snd_seq_midi.
