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Re: CUPS driver/backend question

Dave Camp wrote:
...
I don't see any way for the driver to be able to get status
information back from the printer via the backend. Am I missing
something, or is that how it works? I've seen that the example
backends send status to CUPS via stderr, but not any way for the
driver to get anything back.

CUPS 1.1.x (which is what OSX 10.2 and 10.3 use) does not provide
backchannel support to filters, so you'll need to write an
intelligent backend (see the GIMP-print project for examples of
Epson and Canon specific backends) which sends status info to
CUPS or accesses a driver-specific IPC of your own (shared memory,
message queue, named pipe, etc.) to communicate with your printer
driver filter.

CUPS 1.2 (currently in development, alphas showing up in the not
so distant future) adds both backchannel support and "port monitor"
filters. Backchannel data flows backwards via a pipe on file
descriptor 3 from the backend to all filters, so your filter can
then talk with the device via fd 1 (stdout) and fd 3. The port
monitor filter provides an extra (optional) filter between the
"driver" filter(s) and the backend, allowing for some common
processing of print or backchannel data, insertion of job control
commands, accurate page accounting, etc. There will be a new
PPD attribute which lists the supported port monitors for a
device (including optional URI scheme name for different monitors
for different interfaces...)

The new filter/backend API is backwards-compatible with the current
one, e.g. existing CUPS 1.1.x drivers will still work with 1.2.x...

--
______________________________________________________________________
Michael Sweet, Easy Software Products mike at easysw dot com
Printing Software for UNIX http://www.easysw.com
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References: 
 >CUPS driver/backend question (From: Dave Camp <email@hidden>)



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