Re: Non-hardware devices like loop: another idea

[Mike Snitzer <msnitzer@lnxi.com>]

On Tue, Mar 16 2004 at 23:39,
Alexander E. Patrakov <patrakov@ums.usu.ru> wrote:

> Now I see where the confusion comes from. You misunderstood my proposal. 
> Sorry for not making it clear enough.
> 
> I don't propose to parse these files at all. I want to probe the modules 
> corresponding to the *-major-* aliases unconditionally. Let's review the 
> scenarios for the loop module.
> 
> 1) It is in the kernel. Then the /sys/block/loop0/dev file will be 
> present upon boot, the udev initscript as supplied with the current 
> version of udev will notice it while walking the /sys/block hierarchy, 
> and /dev/loop0 will be created from the initscript.

Cool, I didn't realize this.

> 2) It is a module. Then the modified initscript will notice that there 
> is a block-major line in /lib/modules/<version>/modules.alias with the 
> "loop" as its third field. You suggest to create /dev/loop0 based on 
> this information. I suggest to just call "modprobe loop" instead. The 
> kernel will send the hotplug event and the udev program as supplied in 
> the current udev package will react upon that event by creating /dev/loop0.

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.

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.  

Are there devices that can't and/or shouldn't be hotplug/sysfs-ified?

Mike



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