Re: State of devfs in 2.6?

Greg KH
2003-12-08T23:42:00Z

On Tue, Dec 09, 2003 at 12:04:08AM +0100, Andreas Jellinghaus wrote:
> On Mon, 08 Dec 2003 15:50:45 +0000, William Lee Irwin III wrote:
> > I would say it's deprecated at the very least. sysfs and udev are
> > supposed to provide equivalent functionality, albeit by a somewhat
> > different mechanism.
>
> huh?
>
> aj@simulacron:/dev$ find -type c -mount |grep -v pty |wc -l
> 164
> aj@simulacron:/dev$ find -type b |wc -l
> 157
> aj@simulacron:/dev$ find /sys/ -name dev |wc -l
> 250
>
> After ignoring .devfsd we are left with 70 devices missing:
> - 15 floppy devices

You have 15 floppy devices connected to your box? All floppy devices
should show up in /sys/block.

> - 5 input/ devices

Patch for sysfs support for this has been posted by Hanna Linder. It
still needs work before being added to the kernel tree.

> - full, kmem, kmsg, mem, null, port, random, urandom, zero

Patch for this has been posted by me to lkml in the past. It will
probably go into 2.6.1

> - printers/0

Hanna Linder is working on a patch for these devices.

> - 5 misc/ devices

Patch for this has been posted by me to lkml in the past. It will
probably go into 2.6.1.

> - 12 snd/ devices
> - 5 sound/ devices

I have a patch here from Leann Ogasawara that adds sysfs support for
these devices. I've been lacking time to test it better, but again, it
will probably make it into 2.6.1.

> - 18 vcc/ devices

Hm, good catch. I wonder why these aren't getting picked up in
/sys/class/tty as they are tty devices. I thought they used to be
there...

> I wouldn't call udev deprecated, unless a newer kernel has the
> essential devices, too.

You mean s/udev/devfs/ right? :)

> And is there a udev version that can
> do devfs names? last time I checked only lanana names were supported.

There is a udev config file that was just posted to linux-hotplug-devel
that supports a lot of devfs names. If there are any missing that you
use, please post a config file for them.

Remember, I don't use devfs, so I really don't care about a udev mapping
for it :)

> Some distributions were quite happy to move from /dev and lanana to
> devfs with better names.

Hm, 2? And one of them (Mandrake) got smart and went back...

> I doubt everyone will rush to udev with lanana names,

Why not? It's the standard afterall. Remember, the devfs users are in
the tiny minority here.

> and
> re-introducing makedev for devices not represented
> in sysfs doesn't sound very nice either. So 2.8.* might be a nice time
> frame for dropping devfs, or at least give sysfs and udev a few months
> to catch up on the issues mentioned.

Regardless of the state of udev, devfs has insolvable problems and you
should not use it. End of story.

thanks,

greg k-h