Re: Non-hardware devices like loop: another idea

["Alexander E. Patrakov" <patrakov@ums.usu.ru>]

On Wednesday 17 March 2004 22:01, Mike Snitzer wrote:
> Alexander E. Patrakov wrote:
> > I don't propose to parse these files at all. I want to probe the modules
> > corresponding to the *-major-* aliases unconditionally.

> I wasn't suggesting anything; merely pointed out that your solution was 
> dependent on modules.  Ultimately udev will create /dev entries as it
> walks sysfs (so it takes care of /dev/loopX, etc); but there are aspects
> of the kernel that aren't sysfs-ified (e.g. tun).  Not to mention if the
> devices don't support hotplug udev will never get triggered.

We are talking about different problems here. I am talking about the fact that 
the FAQ says:

Q: But wait, I really want udev to automatically load drivers when they
   are not present but the device node is opened.  It's the only reason I
   like using devfs.  Please make udev do this.
A: No.  udev is for managing /dev, not loading kernel drivers.

Q: Oh come on, pretty please.  It can't be that hard to do.
A: Such a functionality isn't needed on a properly configured system. All
   devices present on the system should generate hotplug events, loading
   the appropriate driver, and udev will notice and create the
   appropriate device node.

I just propose a way of achieving the presence of some devices in /dev when 
the corresponding modules can't support PCI/USB/whatever hardware hotplug 
events at all (is loop a PCI device?). I _assume_ that sysfs is supported 
properly.

> So wouldn't a better option be to make the various devices that don't
> support hotplug and/or sysfs support them? Then udev just needs some new
> rules.  Infering information from the module load (via modules.alias) is
> fragile.

The loop module supports sysfs, and generated hotplug events when inserted or 
removed. The problem is that you cannot make the current hotplug scripts 
insert this module at hardware detection phase. If you know something 
different, please tell us how (based on what information) would you make 
devices such as loop, lp, ppdev (note that they properly support sysfs, but 
can't be detected as hardware) present in /dev? The only other solution 
mentioned here was to keep a big tarball of such undetectable devices and 
untar it every boot.

My approach is better because it also works without modification if I patch my 
kernel and add the pktcdvd module. I will not have to add the pktcdvd devices 
to that tarball.

-- 
Alexander E. Patrakov


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