[cups.general] Opening /dev/usb/lp0 fails while printing

[Michael R Sweet]

Justin Huang wrote:
> I can access my USB printer via /dev/usb/lp0. The printer is a bidi printer, which receives print data from this usb interface (bulk out) and also send status data to the host via the same interface (bulk in).
> I'm planning to create a program which opens /dev/usb/lp0, reads status data and then display some human-readable information. It sounds good, right?
> My problem is... when I launch the program and then make a print, the printer seems to be locked and the print job cannot be sent out from the backend. I'm using open() with O_RDONLY flag. What can I do to allow my program and the backend filter access the printer at the same time? I'm not planning to modify the backend program. Thanks a lot!

You can't, it's a single device and doesn't support multiplexing.

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Michael R Sweet                        Senior Printing System Engineer