USB (libusb) backend needs to print an error message when the open fails

[salfter]

I picked up a Zebra LP2844 cheap off of eBay today...tested it at work under Windows 10, and now I want to get it running at home under Gentoo Linux. CUPS is built with libusb support and /usr/libexec/cups/backend/usb finds the printer and returns usb://Zebra/LP2844?serial=42A062401950 as the printer URL. lpinfo -v shows no indication of the printer, though, and "Find New Printers" in the CUPS web interface returns nothing.

If I enable CONFIG_USB_PRINTING in the kernel source and recompile, plugging in the printer now causes it to show up at /dev/usb/lp0. I can manually configure the printer in CUPS, telling it to print to file:///dev/usb/lp0 (after tweaking /etc/cups/cups-files.conf appropriately), and the test page and a label I knocked together in LibreOffice will priint successfully. If I unload the usblp kernel module and change the printer configuration from the file: URL to the usb: URL, print jobs get stuck. If I reload usblp and change the configuration back to the file: URL, jobs in the queue will finally print.

[michaelrsweet]

What version of CUPS?

What does the /var/log/cups/error_log file show when you run "lpinfo -v"?

[salfter]

I'm running CUPS 2.2.12 on Gentoo Linux. It's built with the following configuration:

[ebuild   R    ] net-print/cups-2.2.12::gentoo  USE="X acl dbus pam python ssl threads usb -debug -java -kerberos -lprng-compat (-selinux) -static-libs -systemd -xinetd -zeroconf" ABI_X86="32 (64) (-x32)" PYTHON_TARGETS="python2_7" 0 KiB

The usb USE flag tells it to build against libusb (and libusb 1.0.21 is installed).

lpinfo -v returns the following:

network https
network ipps
network http
network lpd
network ipp
network socket
network beh
direct hp
network smb

lsusb returns the following...notice that the printer shows up here:

Bus 002 Device 002: ID 8087:8001 Intel Corp.
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 8087:8009 Intel Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 003: ID 045e:00cb Microsoft Corp. Basic Optical Mouse v2.0
Bus 003 Device 002: ID f617:0905
Bus 003 Device 010: ID 0a5f:0009 Zebra LP2844 Printer
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

/usr/libexec/cups/backend/usb returns this:

DEBUG: Loading USB quirks from "/usr/share/cups/usb".
DEBUG: Loaded 95 quirks.
DEBUG: list_devices
DEBUG: libusb_get_device_list=9
DEBUG2: Printer found with device ID: MFG:Zebra ;CMD:None;MDL:LP2844 ; Device URI: usb://Zebra/LP2844?serial=42A062401950
direct usb://Zebra/LP2844?serial=42A062401950 "Zebra LP2844" "Zebra LP2844" "MFG:Zebra ;CMD:None;MDL:LP2844 ;" ""

[salfter]

I'm going to try upgrading to CUPS 2.3.0 to see if that makes a difference.

[salfter]

CUPS 2.3.0 doesn't behave any differently than the older version.

[michaelrsweet]

@salfter I need to see whatever errors are being reported in the CUPS error_log - I suspect you have a permissions issue with the USB device files.

[salfter]

error_log.txt

[michaelrsweet]

OK, I'm not seeing any errors from the USB backend in the error_log; can you try:

sudo -u lp /usr/libexec/cups/backend/usb

to see what the USB backend does when run as the "lp" user?

[salfter]

That returned this:

DEBUG: Loading USB quirks from "/usr/share/cups/usb".
DEBUG: Loaded 95 quirks.
DEBUG: list_devices
DEBUG: libusb_get_device_list=9
DEBUG: Failed to open device, code: -3

Adding the lp user to the usb and lpadmin groups (possible Gentoo packaging issue?) fixed that:

DEBUG: Loading USB quirks from "/usr/share/cups/usb".
DEBUG: Loaded 95 quirks.
DEBUG: list_devices
DEBUG: libusb_get_device_list=9
DEBUG2: Printer found with device ID: MFG:Zebra ;CMD:None;MDL:LP2844 ; Device URI: usb://Zebra/LP2844
direct usb://Zebra/LP2844 "Zebra LP2844" "Zebra LP2844" "MFG:Zebra ;CMD:None;MDL:LP2844 ;" ""

lpinfo -v is unchanged, though:

network https
network ipps
network http
network beh
network lpd
network socket
network ipp
direct hp
network smb

[salfter]

I've also opened an issue over here for the permissions problem found so far, and to pick their brains a bit:

https://bugs.gentoo.org/696898

[michaelrsweet]

I should probably update the backend to send any libusb errors as ERROR: messages as well...

[salfter]

OK, I'm not seeing any errors from the USB backend in the error_log; can you try:

sudo -u lp /usr/libexec/cups/backend/usb
to see what the USB backend does when run as the "lp" user?

I should probably update the backend to send any libusb errors as ERROR: messages as well...

Yes, as no error messages are showing in the log.

If there's a patchset or a git commit I can pull from that'll provide extra logging, I can get it integrated with the build system for testing.

[michaelrsweet]

[master 99c3e9f] Change DEBUG message to ERROR for libusb_init (Issue #5658)

[branch-2.2 f5e0747] Change DEBUG message to ERROR for libusb_init issues (Issue #5658)