Classes and Priorities

[Helge Blischke]

Timetrinus wrote:

>> Timetrinus wrote:
>>
>> > Hello!
>> >
>> > We are creating postscript files that are transferred to 3g / gprs
>> > connected laptops in the field via lpd. For doing this every laptop has
>> > a so called "Mobile" printqueue. This Printqueue defaults to a cups-pdf
>> > backend. But in case the user connects a usb printer the printjob has
>> > to be printed out there instead of creating a PDF.
>> >
>> > I thought about cups classes for automatically handling this behaviour.
>> > So I would create a class Mobile and put in a PDF-Printer and if user
>> > connects a USB Printer add it to this class. But: is it possible to
>> > configure the class to use PDF-Printer only if no other printer is
>> > configured in the queue? Disabeling the PDF-Printer in case the User
>> > connects a USB Printer is not a good Idea because from local
>> > Applications (for example openoffice, or browser) the user should be
>> > able to create PDF output every time.
>> >
>> > Thanks in advance!
>>
>> As for current CUPS, you need to set up sort of a "store and forward"
>> printer which uses a backend script that forwards the job to the real
>> printer if it is connected but otherwise to the pdf-printer.
>> The details of such a configuration depend on the properties of the
>> possible real printers.
>>
>> Helge
>>
> 
> Helge, thank you for reply.
> 
> Can you please point me to the documentation for such a solution? What do
> you mean with "... the properties of the possible real printers." ?
> 
> Thank you!

I'm not aware of any written documentation on this topic, so let me sketch 
out how I think it could work.

As for different properties if connected printers:
if you must account for different make and models to be plugged in on the 
laptops, these printers usually have different set of properties (e. g. 
color or b/w, duplex or not, etc. etc.)

If the printers to be considered have sufficient common properties, you 
could create a PPD describing the common propoerties subset for the "virtual 
printer". Otherwise you need to configure the "virtual printer" as a raw 
printer (possibly with a SYSV interface script for serving special 
requirements).

The Backend for the virtual printer should probably be a script which tests 
if there is a real USB printer online (perhaps by calling the original usb 
backend without parameters) and then either calling the backend for the real 
printer (either the usb or cups-pdf backend) in case of the virtual printer 
having a PPD or printing the data to rhe teal printer, preserving the 
options.

For a more detailed discussion, tell me more about your configuration, cups 
version etc. and contact me off the ng (h dot blischke at acm dot org).

Helge