Inexplicable disk activity trying to load modules on devfs

[Daniel Jacobowitz <drow@false.org>]

I just booted into 2.4.19-pre10-ac2 for the first time, and noticed
something very odd: my disk activity light was flashing at about
half-second intervals, very regularly, and I could hear the disk
moving.  I was only able to track it down to which disk controller, via
/proc/interrupts (are there any tools for monitoring VFS activity? 
They'd be really useful).  Eventually I hunted down the program causing
it: xmms.

The reason turned out to be that I hadn't remembered to build my sound
driver for this kernel version.  Every half-second xmms tried to open
/dev/mixer (and failed, ENOENT).  Every time it did that there was
actual disk activity.  Easily reproducible without xmms.  Reproducible
on any non-existant device in devfs, but not for nonexisting files on
other filesystems.  Is something bypassing the normal disk cache
mechanisms here?  That doesn't seem right at all.

-- 
Daniel Jacobowitz                           Debian GNU/Linux Developer
MontaVista Software                         Carnegie Mellon University