[gentoo-amd64] USB Scanner Problems with Newer Kernels/Libusb

[Frank Peters]

I do not make scans very often, but when I do my scanners work very well
with Linux and Sane -- or at least they used to.

Checking the file dates on my last scans I discover that I last used my
scanner during January of 2012.  This was about the time of the release
of kernel 3.5.  The significance of this is that with kernel 3.5 the usbfs
file system was eliminated.

Previously, libusb was used to read/write to the scanner from user space.
Libusb is still used by Sane but since usbfs has been eliminated it no longer
detects my scanner.

When I plug in the scanner the kernel log shows this message:

Kernel: usb 2-1.4: new full-speed USB device number 4 using ehci-pci

The kernel can detect the device, but the user-space libusb, and hence Sane,
cannot access the scanner.

In fact, sane-find-scanner, which should detect the scanner, fails with this
output:

# Could not initialize libusb-1.0, error -99
# Skipping libusb devices

From what I've manged to find through searches I believe that udev is used
to create devices "on the fly" when a scanner is detected.  However, I've
never used udev before and never had problems with libusb detecting the scanner.
But since usbfs is gone I am now unable to scan due to a failure to detect
the scanner.

The utility usb-devices, which uses libusb, can produce data on the
scanner, but lsusb, which also uses libusb but depends on usbfs, fails.

Does anyone know to resolve such a problem?  How can I get my scanner
to be utilized by libusb and sane?

Frank Peters