Hi, Very interesting, thanks goes to SUSE for working for long time on scanner integration with udev and HAL.
The HAL callout goal would be simply to compute the SANE device name put it to HAL device property scanner.sane.device_name . This does not need any SANE call as long as all backends supports some well known naming scheme along their own specific naming scheme. Then, for scanner specific events (paper-in, adf-opened, "mailto" button pushed, etc.), a HAL addon would fit, but then linking to SANE and requiring 'scanner' privileges. That's how it see it for now. Please comments. Regards, ?tienne.