USB backend never ends if the printer is not connected

[Alejandro Claro]

USB backend never ends if the printer is not connected. We have been able to identify a infinity loop in print_device function in usb-libusb.c file:

```
  fprintf(stderr, "DEBUG: Printing on printer with URI: %s\n", uri);
  while ((g.printer = find_device(print_cb, uri)) == NULL)
  {
    _cupsLangPrintFilter(stderr, "INFO",
    _("Waiting for printer to become available."));
    sleep(5);
  }
```

It's also easy to test by invoking the backend by hand:

```
# export DEVICE_URI='usb://Printer/Model?serial=?'
# /usr/lib/cups/backend/usb 0 root title 1 '' data.file

DEBUG: Loading USB quirks from "/usr/share/cups/usb".
DEBUG: Loaded 159 quirks.
DEBUG: Printing on printer with URI: usb://Printer/Model?serial=?
DEBUG: libusb_get_device_list=6
INFO: Waiting for printer to become available.
DEBUG: libusb_get_device_list=6
INFO: Waiting for printer to become available.
DEBUG: libusb_get_device_list=6
INFO: Waiting for printer to become available.
DEBUG: libusb_get_device_list=6
INFO: Waiting for printer to become available.
DEBUG: libusb_get_device_list=6
INFO: Waiting for printer to become available.
...

```

Setting a job timeout policy or manually stopping work are not options for us. We may have jobs that take hours to complete.

[Alejandro Claro (aclaro)]

We have prepared a patch for the package in Ubuntu 18.04 (CUPS 2.2.7). We would like to request to include a solution like this for at least Ubuntu 18.04.

We also made a pull request in the official CUPS repository:

https://github.com/apple/cups/issues/5817
https://github.com/apple/cups/pull/5818

However, we don't have plans to upgrade or change the distribution we use (Ubuntu 18.04), and this issue is affecting us considerably.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "usb-libusb.c.patch" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Sebastien Bacher (seb128)]

What's the status of the patch upstream? The cups reports mentioned earlier got close asking to report to openprinting instead, did you do that?

[Alejandro (alejandro-claro)]

Hi Sebastian,

the patch set the job state to backend error.

I don't think openprinting is the right error here. The problem is in the backend (the USB backend) when it's not possible to communicate with a USB printer. This usually means that the printer is not connected.

[Till Kamppeter (till-kamppeter)]

Please report on the new GitHub of CUPS on OpenPrinting:

https://github.com/OpenPrinting/cups/issues

On Apple the CUPS project is dead and bug reports probably not read any more.

[Brian Murray (brian-murray)]

Looking at the version of cups in Impish it seems that this change has made it into cups, subsequently I'm setting the bug to fix released.

[Alejandro (alejandro-claro)]

Hi Till,

the issue was reported in the Apple repository:

https://github.com/apple/cups/issues/5817

I will check whether this was already fixed in OpenPrinting or not.