[lug] Help w/udev rules

[Orion Poplawski]

On 09/24/2013 12:20 AM, Maxwell Spangler wrote:
> On a backup server I have two external USB docks.  I'm writing scripts so a
> user can install new offsite backup drives and tell the computer to make them
> available to receive backups.  Another script will copy the appropriate backup
> files to the drives.  For the backup script to work consistently, I want to
> present the removable storage in a predictable manner.
>
> Because these are USB, I've seen their actual drive devices in /dev change
> letters based on a variety of factors.
>
> So I'm trying to use udev rules to make this predictable:
>
> 1) User installs drive and powers on the dock
> .. works
>
> 2) udev uses standard rules to identify a storage device and create /dev/sdf
> (for example)
> .. works
>
> 3) I have installed a user rule which is specific to this USB3 dock and
> piggybacks a little more onto step 2:  It will create a symlink from /dev/sdf
> to /dev/usb3dock so that my scripts can use /dev/usb3dock as a predictable
> location.
> .. works
>
> At least while developing this remotely (without actually power cycling the
> dock), it appears as though udev will correctly identify /dev/sdf as the USB3
> dock and correctly make a symlink to /dev/usb3dock, but it fails to load the
> partitions on the drive and create /dev entries for them.
>
> If you've worked with udev can you tell me if that should be happening?
>
> My work-around tonight was to insert a small bash script into the custom udev
> rule, call it, and run partprobe.
>
> With a little more work involving two udev rules and a custom script, I can
> see udev wake up six times* and everything is working.  I'd like to know if
> I'm followng best practices or whether this is a hack that works.
>
> * six times: one for /dev/sdf, one for the symlink'd /dev/usb3dock, two for
> /dev/sdf1 and /dev/sdf2, and two for /dev/usb3dock1 and /dev/usb3dock2.
>
> It's been a long night of fighting with udev but I'm happy it seems I've won.

I'm no udev expert, and it's hard to tell without seeing your udev entries. 
But disks and partitions are often handled differently


-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA, Boulder/CoRA Office             FAX: 303-415-9702
3380 Mitchell Lane                       orion at nwra.com
Boulder, CO 80301                   http://www.nwra.com