[sane-devel] udev updates /dev/..., sane accesses /proc/...

[Felix E. Klee]

I've installed sane-backends-1.0.18 on a Slackware 10.2 system with
kernel 2.6.14.4 and libusb 0.1.12.  Also, I've installed the udev rules
that are part of the sane backends, just as explained in README.linux:

  cp sane-backends-1.0.18/tools/udev/libsane.rules \
  /etc/udev/rules.d/50-libsane.rules

Now, when run as root, "scanimage -L" outputs:

  device `snapscan:libusb:001:002' is a EPSON EPSON Scanner flatbed
  scanner

When run as an ordinary user, however, "scanimage -L" outputs:

  No scanners were identified. If you were expecting something
  different, check that the scanner is plugged in, turned on and
  detected by the sane-find-scanner tool (if appropriate). Please read
  the documentation which came with this software (README, FAQ,
  manpages).

The reason seems to be quite simple:

- The sane udev rules update the permissions of the file
  "/dev/usbdev1.3".

- Sane accesses "/proc/bus/usb/001/002".  When I update the permissions
  of "/proc/bus/usb/001/002" manually, then "scanimage -L" also works
  for the ordinary user.

It seems that something is missing from README.linux.  But what?  How do
I make the scanner accessible to ordinary users?  Why does sane access a
device node in /proc/ - isn't that pervert?

I forgot: The scanner is an Epson Perfection 3490 Photo.

-- 
Felix E. Klee