[systemd-devel] Counting mechanism in udev rules

[Robert Milasan]

On Fri, 14 Dec 2012 11:30:05 +0100
"Kay Sievers" <kay at vrfy.org> wrote:

> On Fri, Dec 14, 2012 at 9:11 AM, Robert Milasan <rmilasan at suse.com>
> wrote:
> > Is there some kind of a counting mechanism which can be used in a
> > udev rule?
> >
> > I got this rule:
> >
> > ACTION=="add", SUBSYSTEM=="3270", KERNEL=="tty0.0.[0-9]*",
> > SYMLINK+="3270/ttycons-%n"
> >
> > and the result of this rule looks like this:
> >
> > lrwxrwxrwx 1 root root 14 Dec 13 15:28 ttycons-0500
> > -> ../tty0.0.0500 lrwxrwxrwx 1 root root 14 Dec 13 15:28
> > ttycons-0501 -> ../tty0.0.0501 lrwxrwxrwx 1 root root 14 Dec 13
> > 15:28 ttycons-0502 -> ../tty0.0.0502 lrwxrwxrwx 1 root root 14 Dec
> > 13 15:28 ttycons-0503 -> ../tty0.0.0503
> >
> > But I would like instead of '%n' to use a counting variable that
> > would make the result look something like this:
> >
> > lrwxrwxrwx 1 root root 14 Dec 13 15:28 ttycons0 -> ../tty0.0.0500
> > lrwxrwxrwx 1 root root 14 Dec 13 15:28 ttycons1 -> ../tty0.0.0501
> > lrwxrwxrwx 1 root root 14 Dec 13 15:28 ttycons2 -> ../tty0.0.0502
> > lrwxrwxrwx 1 root root 14 Dec 13 15:28 ttycons3 -> ../tty0.0.0503
> >
> > Would this be possible in udev, if so what '%' option can I use?
> 
> There is intentionally no enumeration facility in udev. Udev-provided
> enumeration would not be much better than the kernel-provided
> enumeration.
> 
> In general, all sorts of device inter-dependencies in device names
> should be avoided, and names should be provided by properties derived
> from the device itself, the bus location it is connected to, or be
> supported by the firmware, and not by unreliable enumeration.
> 
> "Inventing" new numbers in a device hotplug path cannot really work,
> and udev does not want to give the impression it could.
> 
> Kay
> 

OK, I understand, but if I would like to achieve what I wrote, how would
I go and do that?

-- 
Robert Milasan

L3 Support Engineer
SUSE Linux (http://www.suse.com)
email: rmilasan at suse.com
GPG fingerprint: B6FE F4A8 0FA3 3040 3402  6FE7 2F64 167C 1909 6D1A