Re: devfs vs. udev

[Greg KH <greg@kroah.com>]

On Tue, Oct 07, 2003 at 02:38:27PM +0200, Måns Rullgård wrote:
> 
> I noticed this in the help text for devfs in 2.6.0-test6:
> 
> 	  Note that devfs has been obsoleted by udev,
> 	  <http://www.kernel.org/pub/linux/utils/kernel/hotplug/>.
> 	  It has been stripped down to a bare minimum and is only provided for
> 	  legacy installations that use its naming scheme which is
> 	  unfortunately different from the names normal Linux installations
> 	  use.
> 
> Now, this puzzles me, for a few of reasons.  Firstly, not long ago,
> devfs was spoken of as the way to go, and all drivers were rewritten
> to support it.  Why this sudden change?

A few things happened:
	- the devfs maintainer/author disappeared and stoped maintaining
	  the code.
	- devfs was found to have unfixable bugs
	- it was determined that the same thing could be done in
	  userspace (like udev.)
	  
> Secondly, that link only leads me to a package describing itself as an
> experimental proof-of-concept thing, not to be used for anything
> serious.  How can something that incomplete obsolete a working system
> like devfs?

I didn't send that patch to the kernel to mark devfs as such.

Actually devfs is still very much "experimental" and "proof-of-concept"
if you have ever looked at it's code :)

> Thirdly, udev appears to respond to hotplug events only.  How is it
> supposed to handle device files not corresponding to any physical
> device?

Like what?  Anything that shows up in sysfs, udev will handle.  It's
only a matter of getting everything to show up in sysfs now...  It's
almost all there.

> Finally, I quite liked the idea of a virtual filesystem for /dev.  It
> reduced the clutter quite a bit.  As for the naming scheme, it could
> easily be changed.

devfs's naming scheme could easily be changed?  Hahaha...

udev will be a major factor of improvement for changable naming schemes.
Please read the OLS paper for more details.

thanks,

greg k-h