In /etc/udev/rules.d/sane.rules, the script /lib/udev/libusbscanner.sh is called to set the permissions and ownership of the scanner device in /proc/bus/usb/BBB/DDD, such that users in group "scanner" can use the scanner. Unfortunately, this does not work if the scanner is plugged in when the system is rebooted. You have to unplug the scanner and plug it back in again to get the right permissions. This appears to be because module autoloading loads the usb modules before /proc/bus/usb is mounted. I fixed this by blacklisting the usbcore module in /etc/rc.conf. It is then loaded towards the end of /etc/rc.sysinit, where /proc/bus/usb is mounted. I have not altered rc.sysinit.

Is blacklisting usbcore the right thing to do?