udevadm

You can use udevadm to see the variables set by udev for a device. This is helpful if you want to get information about the device, based on whether it has a DVD or a CD in there, for example.

udevadm info /dev/sr0

If you want to change any rules, such as in /lib/udev/rules.d or /etc/udev/rules.d, you can reload them with udevadm as well:

udevadm trigger

That's what I use when doing my onevent trayclose calls.