According to the changelog, beginning with version 1.5.3, cups requires libusb:1 instead of the old libusb:0.
CHANGES IN CUPS V1.5.3
- The USB backend now uses and requires LIBUSB 1.0 or later (STR #3477)
I can confirm this for cups 1.6.1:
$ readelf -d /usr/libexec/cups/backend/usb
Dynamic section at offset 0x7b48 contains 26 entries:
Tag Type Name/Value
0x0000000000000001 (NEEDED) Shared library: [libusb-1.0.so.0]
0x0000000000000001 (NEEDED) Shared library: [libcups.so.2]
0x0000000000000001 (NEEDED) Shared library: [libpthread.so.0]
0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
libusb-1.0.so.0 hereby belonging to dev-libs/libusbx-1.0.12.
Please change this accordingly.
Created attachment 323286 [details]
emerge --info cups
Using hwids-20130309-r1 and /udev-198-r1, cups-1.6.1, and cups-1.5.3 fails to work with my usb Samsung ML-1450 printer, while cups-1.5.2-r4 works just fine. I presume is has to do with hwids or udev from the other comments, but I'm not clear what to do with those.