Re: new version of udev has different cd/dvd devices

[Kay Sievers <kay.sievers@vrfy.org>]

On Thu, Dec 29, 2005 at 11:46:59PM -0800, Greg KH wrote:
> On Thu, Dec 29, 2005 at 12:29:36AM +0100, Kay Sievers wrote:
> > On Wed, Dec 28, 2005 at 11:50:00PM +0100, Marco d'Itri wrote:
> > > On Dec 28, Moshe Yudkowsky <msha5_17@bl.com> wrote:
> > > 
> > > > The latest udev (0.079) puts the second drive only for /dev/cdrom, cdrw, 
> > > >  dvd, and dvdrw.
> > > Do not use %e in rules.
> > 
> > Yes, %e will be removed in one of the next versions for that reason. It
> > never worked reliably outside of udevstart, which is no longer
> > recommended to use.
> 
> Yeah, but we still need a way to enumerate devices in some kind of
> order, like we do for the cdrom devices today.  So I don't think we can
> drop it entirely.

We don't have any "order", that's why we can't do it that way. The
persistent /dev/disk links are working without any "order", that's the
model to follow, or writing out "automatic rules" to provide stable names.
Everything else will just not work.

> > Yuu can match on ENV{ID_PATH} with custom rules for every device. On
> > SUSE, the system management creates rules on installation or update, to
> > have always the same names for optical drives, regardless of the order
> > of discovery:
> > 
> >   $ cat /etc/udev/rules.d/65-cdrom.rules
> >   # cdrom links generated by YaST2
> >   #
> >   SUBSYSTEM="block", ENV{ID_PATH}="pci-0000:00:1f.2-scsi-1:0:0:0", SYMLINK+="cdrecorder cdrom"
> > 
> > Distros could also have a "default" rule, which catches unconfigured
> > devices and automatically creates a rule for them to keep the name
> > stable across reboots.
> 
> Or we can just stick with the rules we have today that use %e just fine,
> as it emulates exactly what a static /dev would have done, and no one is
> complaining about it :)

No, %e doesn't work "fine" without udevstart. Device names switch with
every reboot, depending on random device response and process running
time, which is unacceptable and %e must be avoided for that reason. And
worse, %e does not use locking, so for parallel probing, it will return
the same names for different devices, if they are requested in parallel
in a short timeframe.

Kay


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