[cups.general] Appropriate permissions for printer device files?

[Stefan Fiedler]

Hi all!

CUPS 1.2.5 works with my USB printer (a Canon S400) only if permissions on the 
respective device file (/dev/usb/lp0) are changed from
    crw-rw---- 1 root root 180, 0 2006-11-04 23:13 /dev/usb/lp0
to
    crw-rw-rw- 1 root root 180, 0 2006-11-04 23:13 /dev/usb/lp0

Now I don't want the device to be read-/writeable by everyone; but running 
cupsd and the backends with setuid (root) permissions instead doesn't work.

CUPS 1.1.x worked "out of the box" without changing any permissions, although 
I can't see any obvious differences in file permissions between the two 
installations.

My question: which binaries access printer devices directly and hence have to 
run with setuid root, or is there another solution to this problem?
Please note that I'm interested in all CUPS binaries that access printer 
devices, not only USB devices, if there is more than one.

Thanks in advance,
    Stefan Fiedler