[Printing-architecture] 'driverless' doesn't find CUPS shared print queues - expected or a bug?

Till Kamppeter till.kamppeter at gmail.com
Tue Jun 8 08:58:40 UTC 2021


What you have observed is correct.

The "driverless" utility filters out remote CUPS queues, as its 
intention is to retro-fit driverless printer support into classic 
printer setup tools which do not support driverless printing by themselves.

"driverless" here emulates the presence of a driver. When correctly 
installed it is linked into both the /usr/lib/cups/backend and 
/usr/lib/cups/driver directory. In the former it provides discovery of 
the supported driverless IPP printers with correct IPP URIs ("lpinfo -v" 
or equivalent API/IPP calls). This way the printer setup tool discovers 
the printers in question and shows them as network printers.

The link into /usr/lib/cups/driver makes the utility being run (with 
"list" argument) when CUPS is searching for PPD files/drivers ("lpinfo 
-m" or equivalent API/IPP calls). Here the tool runs ippfind again and 
shows for each printer a PPD URI. This makes the printer setup tool 
listing a "driver" for the discovered IPP printer, named "driverless".

Selection of this "driver" ("lpadmin ... -m PPD URI" or equivalent 
API/IPP calls) makes the tool being called with "cat PPD URI" command 
line argument and this way it does an get-printer-attributes IPP request 
on the printer and generates a PPD file based on the result.

As remote CUPS queues are auto-setup by cups-browsed you usually do not 
set them up with a printer setup tool. therefore I suppressed these 
queues in the result of "driverless", to avoid clutter in printer setup 
tools.

Note that https://github.com/OpenPrinting/cups-filters/issues/375 is 
actually a bug. ippfind actually exits with 1 if there is no suitable 
printer found, whereas a CUPS backend in discovery mode should exit with 
0 if no suitable printer got found.

    Till


On 07/06/2021 08:29, Zdenek Dohnal wrote:
> Hi Till,
> 
> I have an bug which I can reproduce in my LAN 
> (https://bugzilla.redhat.com/show_bug.cgi?id=1954469) and in that bug 
> Solomon reported a problem which he has with driverless in his setup.
> 

[...]



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