cups banners, scheduling and interoperability questions

[David Decotigny]

Hi,


1st question
------------

We have the following configuration : 1 cups server, 1 printer (HP 
Postscript over ethernet), *2 queues* for this printer (1 for duplex, 1 
for single-side printing, for historical reasons), multiple unix clients 
(cups client). And, for each job we want to print *a banner*.

The question is : if 2 clients send their printing requests to the 
server "at the same time" on the 2 queues, could the jobs' banner and 
document pages interleave ?

I mean: client A sends a job on queue Q1 with the banner "A_banner" and 
the document contents "A_contents", and at the same time client B sends 
"B_banner" and "B_contents" on the other queue Q2: could it happen that 
the server schedules the 2 jobs (banner + contents) in the following order :
   A_banner
   B_banner
   A_contents
   B_contents
.... so that the pages are interleaved on the printer ?

For what I understand, 1/ cups actually treats the banner and the 
document contents as 2 distinct tasks and 2/ cups sees 2 distinct queues 
and does not care whether these queues correspond to the same physical 
resource (the printer). So I think this can actually happen... please 
tell me I am wrong...

If I am unfortunately right, is there a way to change this behavior in 
the cups configuration ? Where to look at in the source code to make the 
change ?

Related question : and if there were only ONE queue for the printer, are 
we assured that the banner and document contents will never interleave ? 
ie that we'll allways have something like:
   A_banner
   A_contents
   B_banner
   B_contents
In that case, a dirty hack would be to define 3 queues: 1 "top-level 
queue" for the physical printer (not available to the clients), and the 
2 "client-level queues" available to the clients that simply redirect 
their jobs to the "top-level queue". But this raises another question: 
where should the banner be printed ?
   - By the "top-level queue" only ? But what about the 
"job-originating-user-name" and "job-originating-host-name" 
substitutions in the banner ? will they be set to "root" and "localhost" 
(because the client-level queues sending the jobs to it are run by 
cupsd, ie by by root on localhost) ?
   - By the "client-level queues" ? but in that case, is it sure that 
the banner and documents contents will NOT interleave ? Because it seems 
that it is equivalent to printing 2 distinct pairs of job 
(A_banner+A_contents and B_banner+B_contents), so that in the end we 
could still get the wrong schedule:
   A_banner
   B_banner
   A_contents
   B_contents
(depending on the way the OS schedules the connections from the 
"client-level queues" to the "top-level queue" server socket) Am I wrong ?

I'd be happy if cups effectively schedules two queues targetting the 
same physical printer as one single physical resource ! I'd be equally 
happy if cups can send both the banner and the job contents over the 
same TCP connection !


2nd question
------------

Now imagine we have windows machines. If the windows machines don't 
print through the cups server, obviously they can interleave their jobs 
between a cups banner and the associated document. Ie we can have (and 
we DO have) :
   Unix_banner
   Windows_job
   Unix_contents
Which is a bit annoying. The problem comes from the fact that the banner 
and the document's content are 2 distinct jobs from the printer's point 
of view. The 1st question was related to internal cups scheduling, this 
one is more independent on cups. Am I wrong ?

So, what is the best solution to make the windows machines print through 
the cups server, which would centralize the scheduling of the jobs ?
   - setup a samba server on the cups server ? I tried it, with the cups 
server printing the banner. But the "job-originating-user-name" and 
"job-originating-host-name" always say "nobody"/"localhost" (which is 
normal since the smb stuff is run as nobody on the cups server). I also 
tried to make the windows client include the banner at the beginning of 
its job (windows printer "properties" wizard), but for a strange reason, 
the printer does not print it...
   - Is there another way to do this ? IPP (how on windows clients ?) ? 
Will the "job-originating-user-name" and "job-originating-host-name" 
substitutions reflect the correct user/host name ?

(re) I'd be happy if cups can send both the banner and the job contents 
over the same TCP connection !

Thanks a lot in advance for your answers !

-- 
David Decotigny -- LLR -- http://polywww.in2p3.fr