Re: Problem in udev with %e device numbering

[Michael Gutmann <gutmann@uni-duesseldorf.de>]

Hello Kay,
sorry for bothering you, but maybe you can help me out with 
understanding the underlying problem.

On Sat, 2005-01-29 at 20:53 You wrote:
> On Sat, 2005-01-29 at 18:53 +0100, Michael Gutmann wrote:
<...>
> > card is put into the card reader. Unfortunately they are only found if
> > something tries to use the card, f.e. fdisk.
>
> If you don't use anything that polls the device for a media change,
> which is what all major desktop installation do today, you don't get
> these nodes, yes.

Sorry, didn't want to blame udev for doing this. I was rather 
disappointed, that the card reader didn't announce changes itself ;-)

> > So I have to use NAME(all_partitions}. No problem so far, but I want to
> > use symbolic names instead of sd?. But if I use SYMLINK="cardreader%e"
> > f.e. there are only links to sd[abcd] and not to the partitions.
> > The only way I see is using NAME{all_partitions}="card%e".
>
> There is no sane way to use the %e key in cases you get concurrent
> events asking for enumeration of the same name. It's a too simple hack
> and there is no way with the current udev model to get this fixed inside
> of udev.

Oh shit. I get your point:

Jan 30 11:17:47 localhost kernel: usb-storage: device found at 2
Jan 30 11:17:48 localhost kernel: usb-storage: waiting for device to settle before scanning
Jan 30 11:17:48 localhost usb.agent[5358]:      usb-storage: loaded successfully
Jan 30 11:17:52 localhost kernel:   Vendor: Generic   Model: Flash R/W         Rev: 2002
Jan 30 11:17:52 localhost kernel:   Type:   Direct-Access                      ANSI SCSI revision: 02
Jan 30 11:17:52 localhost kernel: Attached scsi removable disk sda at scsi0, channel 0, id 0, lun 0
Jan 30 11:17:52 localhost kernel:   Vendor: Generic   Model: Flash R/W         Rev: 2002
Jan 30 11:17:52 localhost kernel:   Type:   Direct-Access                      ANSI SCSI revision: 02
Jan 30 11:17:52 localhost kernel: Attached scsi removable disk sdb at scsi0, channel 0, id 0, lun 1
Jan 30 11:17:53 localhost udev[5456]: configured rule in '/etc/udev/rules.d/10_micha.rules' at line 3 applied, 'sda' becomes 'card%e'
Jan 30 11:17:53 localhost udev[5481]: configured rule in '/etc/udev/rules.d/10_micha.rules' at line 3 applied, 'sdb' becomes 'card%e'
Jan 30 11:17:53 localhost kernel:   Vendor: Generic   Model: Flash R/W         Rev: 2002
Jan 30 11:17:53 localhost kernel:   Type:   Direct-Access                      ANSI SCSI revision: 02
Jan 30 11:17:53 localhost kernel: Attached scsi removable disk sdc at scsi0, channel 0, id 0, lun 2
Jan 30 11:17:53 localhost udev[5499]: configured rule in '/etc/udev/rules.d/10_micha.rules' at line 3 applied, 'sdc' becomes 'card%e'
Jan 30 11:17:53 localhost kernel:   Vendor: Generic   Model: Flash R/W         Rev: 2002
Jan 30 11:17:53 localhost kernel:   Type:   Direct-Access                      ANSI SCSI revision: 02
Jan 30 11:17:53 localhost udev[5499]: creating device node '/dev/card0'
Jan 30 11:17:53 localhost udev[5499]: creating device partition nodes '/dev/card0[1-15]'
Jan 30 11:17:53 localhost udev[5481]: creating device node '/dev/card0'
Jan 30 11:17:53 localhost udev[5481]: creating device partition nodes '/dev/card0[1-15]'
Jan 30 11:17:53 localhost udev[5456]: creating device node '/dev/card0'
Jan 30 11:17:53 localhost udev[5456]: creating device partition nodes '/dev/card0[1-15]'
Jan 30 11:17:53 localhost kernel: Attached scsi removable disk sdd at scsi0, channel 0, id 0, lun 3
Jan 30 11:17:53 localhost kernel: usb-storage: device scan complete
Jan 30 11:17:53 localhost udev[5522]: configured rule in '/etc/udev/rules.d/10_micha.rules' at line 3 applied, 'sdd' becomes 'card%e'
Jan 30 11:17:53 localhost udev[5522]: creating device node '/dev/card1'
Jan 30 11:17:53 localhost udev[5522]: creating device partition nodes '/dev/card1[1-15]'

But here I get into trouble: with kernel 2.6.10 device numbering is 
serialized dependent on the physical device (as I understood the 
discussion last december) As you can see, the different parts of the
card reader are identified as luns. Isn't it possible to identify the
physical device behind that luns and serialize the numbering for it?

> The only sane solution, I can imagine would be an external program, that
> does the enumeration and returns the value to udev. This external
> program would need to maintain its own database in a dotfile in /dev and
> must use a file lock to serialize concurrent processes asking for the
> value. This topic was already discussed on this list, you may look at
> the archives...

Argh, this misses the elegance I marvel at udev.

> Kay

Thanks,
Michael


-- Michael Gutmann
Multimediazentrum Heinrich-Heine-Universität Düsseldorf
D-40225 Düsseldorf, Moorenstr. 5, Geb. 14.77
Tel.: +49 211 81 19730, Fax:  +49 211 81 19741


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