Hard Disk device IDs in Linux

Corey Edwards tensai at zmonkey.org
Tue Mar 12 13:31:08 MDT 2013


On 03/12/2013 11:54 AM, Nicholas Leippe wrote:
> On Tue, Mar 12, 2013 at 12:31 AM, Dan Egli <ddavidegli at gmail.com> wrote:
>>
>> *Well, that's interesting. I've seen udev before. I know Gentoo makes heavy
>> use of it (or at least it did last I looked). I still wonder about that. If
>> everyone likes the things that udev does, then why did they clobber devfs
>> out of the kernel all those years ago? devfs and udev were very similar.
>> The biggest difference that I can see (and I admit I haven't looked closely
>> at udev beyond making sure it was running back when I had a Gentoo box all
>> those years ago) was that udev had the option of creating customized device
>> filenames automatically where as devfs had the device filenames fixed in
>> the kernel. But then that was what devfsd was supposed to be for in the
>> first place. Not only did it create symlinks to the actual device files
>> that were present in the devfs, but I was under the impression that you
>> could also instruct it to create custom symlinks as well that would still
>> point to the correct device files. Maybe I'm wrong, but that's my memory at
>> least.*
> 
> I don't remember the exact details--it's been years. But devfs, while
> good for its day, was more of a stop-gap and was severely broken in
> many respects--the kernel devs were happy to see it go. Udev is the
> solution devfs was meant to be, and is far superior.

One major difference is that udev runs entirely in user space where
devfs ran in kernel space. History has born out that udev was the
correct way to go.

The flame wars over udev v sysfs are almost as interesting as those
between Linus and Tanenbaum. Somebody should make a play about them.

Some good reading:

http://lists.debian.org/debian-user/2004/11/msg02647.html
http://kerneltrap.org/node/1893

Corey



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