Data flow through CUPS

[Michael Sweet]

Sebastian James wrote:
> ...
> Initially I thought I would change cups-lpd and some raw input
> programs to spool data in chunks. The filters in this device simple
> pass the data through to the backends (parallel and usb). This means
> that the backend is likely to be passed a portion of a printjob,
> which it'll spool to the printer. There shouldn't be and difficulties
> with this, should there, as long as the next portion of the job is
> spooled fairly soon after?

Ok, that sounds like you would be using cups-lpd to provide an
embedded implementation of LPD, not IPP, right?

In that case, I'd just hack up cups-lpd to read a printcap file
(or have one hardcoded in the program) which maps queues to UNIX
devices and does an exclusive open on the port when printing.
Then you can just write the data files to the port instead of to
disk...

> 2: The filenaming convention of cups data files is d00001-001 for the
> first print job and d00002-001 for the second job and so on. Under
> what circumstances does the -001 increment to -002? Initially I
> thought, "oh must be page number" but how are the filters to know or
> care what the page number of the print job is? I'd very much
> appreciate a short explanation of how this works.

cupsd (the IPP server) writes these files in response to requests
from clients.  They start out as temporary files (0000000, 00000001,
etc.) and are renamed as needed.  The -001 refers to the first file
in the job, -002 is the second, and so forth.

-- 
______________________________________________________________________
Michael Sweet, Easy Software Products           mike at easysw dot com
Internet Printing and Document Software          http://www.easysw.com