You can't do that. What you can do, however, is create a named pipe in the
/dev directory with the mknod program. Then write an optisafed which will
open the pipe for write, select(2) on it, then when woken, get the info from
the UPS, process it, and send output to the pipe.
In theory, you could also use the userfs and a userspace program that
created a filesystem based on data from the UPS. This would be overkill.
Evan