Re: Inexplicable disk activity trying to load modules on devfs

[Richard Gooch]

Borsenkow Andrej writes:
> >> 
> >> 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. 
> >> 
> >
> >
> >syslog activity from a printk, perhaps? 
> 
> No. It is most probably devfsd trying to load sound modules.
> 
> This is exactly the reason Mandrake does not enable devfs in
> kernel-secure.  You can badly hit your system by doing in a loop ls
> /dev/foo for some device foo that is configured for module
> autoloading.
> 
> It is very fascist decision; the slightly more forgiving way is to
> disable devfsd module autoloading (or disable devfsd entirely, just
> run it once after all drivers are loaded to execute actions) but
> then you lose support for hot plugging and some people do use
> kernel-secure on desktops.

Or you can use the IGNORE action to selectively disable loading of
some modules (whether or not they exist).

Another option is to write a shared object extension to devfsd which
has rate-limiting. All the mechanisms you need are there or can be
built on top of the existing infrastructure.

				Regards,

					Richard....
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