I am in the process of upgrading to Leap 42.1 from 13.2, getting everything
right on an old machine before wiping the disk on my regular machine. I am
unable to get the scanner to be recognized. It was not straightforward under
13.2 where I went through these steps:

1. Download hp3900-series tar file from
http://sourceforge.net/projects/hp3900-series/ and run INSTALL.sh

2. Add
# HP Scanjet G3110
usb 0x03f0 0x4305
to /etc/sane.d/hp3900.conf

3. Add
# Hewlett-Packard ScanJet G3110
ATTR{idVendor}=="03f0", ATTR{idProduct}=="4305", MODE="0664", GROUP="lp",
ENV{libsane_matched}="yes"
to /etc/udev/libsane.rules

4. Add
hp3900
to /etc/sane.d/dll.conf

5. Install hplip

6. Go to Yast -> Hardware -> Scanner
and attempt to configure the scanner.

Under Leap 42.1 the Scanner Configuration window contains these two items in
the list:
hp3900 No scanner recognized by this driver
Not Configured hewlett packard hp scanjet USB scanner (vendor=0x03f0 [hewlett
packard]) at libusb:001:003

When I select the last one and click on Edit, I get a list of types of scanner.
I select the G3110 and click Next, but it refuses to be configured.

Running sane-find-scanner gives
found USB scanner (vendor=0x03f0 [hewlett packard], product=0x4305 [hp
scanjet]) at libusb:001:003

When I turned on level 4 debugging, I got:
# export SANE_DEBUG_DLL=4
# scanimage -d  "hp3900:libusb:001:003" -v >/dev/null && echo OK || echo FAILED
[sanei_debug] Setting debug level of dll to 4.
[dll] sane_init: SANE dll backend version 1.0.13 from sane-backends 1.0.24
[dll] sane_init/read_dlld: attempting to open directory `./dll.d'
[dll] sane_init/read_dlld: attempting to open directory `/etc/sane.d/dll.d'
[dll] sane_init/read_dlld: opendir failed: No such file or directory
[dll] add_backend: adding backend `hp3900'
[dll] add_backend: adding backend `hpaio'
[dll] sane_open: trying to open `hp3900:libusb:001:003'
[dll] load: searching backend `hp3900' in `/usr/lib64/sane'
[dll] load: trying to load `/usr/lib64/sane/libsane-hp3900.so.1'
[dll] load: dlopen()ing `/usr/lib64/sane/libsane-hp3900.so.1'
[dll] load: dlopen() failed (/usr/lib64/sane/libsane-hp3900.so.1: wrong ELF
class: ELFCLASS32)
scanimage: open of device hp3900:libusb:001:003 failed: Invalid argument
[dll] sane_exit: exiting

The library /usr/lib64/sane/libsane-hp3900.so.1 that I was using under 13.2 is
different from what I had downloaded from Sourceforge. When I relinked
/usr/lib64/sane/libsane-hp3900.so to libsane-hp3900.so.1.0.24 (that works under
13.2) instead of libsane-hp3900.so.1.1.0 (which came from Sourceforge),
scanimage works if I specify the address of the scanner precisely:
scanimage -d  "hp3900:libusb:001:003" -v >/tmp/scan.jpg
However, XSane does not find the scanner and I am unable to configure it using
YaST.

I have removed hplip and it makes no difference. The fully specified scanimage
works but XSane cannot find the scanner.