Creating /dev links to dynamic devices

devfs.conf allows creating static device links:

link	acd0	cdrom

This only runs on devfs startup, so it's useless for creating a link to 
a dynamic device.

The specific example is for scanners.  My scanner is ugen2.3, but only 
as long as it is plugged into the same USB hub/port each time.  I can 
manually create a uscanner0 link in /dev with devd.conf:

attach 20 {
         device-name "ugen[0-9]+";
         match "vendor" "0x04b8";
         match "product" "0x010a";
         action "/bin/ln -sf /dev/$device-name /dev/uscanner0; /sbin/devfs rule applyset";
};

Using /dev/uscanner0 then works in place of ugen2.3.

Now the second part of the example: I want devd to recognize the attach 
or creation of uscanner0.  But it's not a true devfs device; devd 
doesn't see an attach event, or a notify CDEV/CREATE event.

Is there a method to create a true devfs link to a dynamic device?

-Warren Block * Rapid City, South Dakota USA