Match device using udev

Kindly written by Chris Vogel (@chri2), explaining how can a specific device be matched with a udev rule, so you can differentiate between multiple devices on the same machine:

Make udev ask the hardware database using deskhops serial number

On my system the default udev rules do not include the information about the serial number when asking the hardware database for extra information about a device.

/etc/udev/rules.d/59-evdev.rules:

ACTION=="remove", GOTO="evdev_end"
KERNEL!="event*", GOTO="evdev_end"

# Device matching the input device name and the S/N (used for Deskhop)
KERNELS=="input*", \
  IMPORT{builtin}="hwdb 'evdev:sn:$attr{name}:$attr{uniq}'", \
  ENV{.HAVE_HWDB_PROPERTIES}="1"

LABEL="evdev_end"

The filename is chosen, so that this rule would run before my default rule for evdev named /lib/udev.d/rules/60-evdev.rules. You might need to change the filename for your system accordingly. /lib/udev.d/rules/60-evdev.rules contains IMPORT{builtin}="keyboard" which should run after the new rule.

Add extra information for the keyboard attached to deskhop

The device match above will lookup the hardware database for a section evdev:sn:<deskhop name>:<deskhop s/n>. I added it to the database:

/etc/udev/hwdb.d/59-keyboard.hwdb:

# deskhop with S/N
evdev:sn:Hrvoje Cavrak DeskHop Switch Keyboard:xxxxxxxxxxxxxxxxx
 KEYBOARD_KEY_7004a=insert
 KEYBOARD_KEY_70049=home

To get the xxxxxxxxxxxxxxxxx part (serial number) I used lsusb -d2e8a:107c -v | grep -i serial which outputs something like

# lsusb -d2e8a:107c -v | grep -i serial
  iSerial                 3 xxxxxxxxxxxxxxxxx

The first digit seperated by space from the S/N is not part of the number - in my example the 3.