[cups] Configuration of Client-Side Avahi browsing

[Johannes Meixner]

Hello,

I am really not an expert here but as far as I know it is
basically as follows:

Since CUPS 1.6 networking "printer" discovery does no longer
happen via CUPS' own traditional "CUPS Browsing" method
but instead via DNS-SD.

For DNS-SD under Linux CUPS is liked with Avahi.

Basically - as far as I understand it - it is primarily Avahi
that gets all incoming DNS-SD information in particular
information about "printers" in the network that advertise
themselves via DNS-SD.

I wrote "printer" because what actually such a "printer" is
depends on what actually submits DNS-SD information into
the network.

For example network printer devices can advertise themselves
via DNS-SD so that in this case a "printer" is a real piece
of hardware.

But also CUPS > 1.6 can advertise its print queues via DNS-SD
so that in this case a "printer" is not a real piece of hardware
but some kind of abstract representation (i.e. a print queue).

All kind of DNS-SD "printer" information is collected by Avahi
and applications can gets this information directly from Avahi.

For example - as far as I know - GTK printing dialog widgets
can do this and - as far as I know - GTK can do this also
without a locally running cupsd because GTK can ask
directly Avahi for the DNS-SD "printer" information.


On Nov 23 14:07 Alexander Hofmann wrote (excerpt):
> I'm currently trying to find the portion of code adding hundreds of
> printers to my "Print Document"-Dialog by querying Avahi. I first
> accused GTK of doing this, but it seems that cups now has this feature
> it self...

I guess it is GTK that gets it directly from Avahi
(but I do not know about GTK internals)
regardless that also CUPS has DNS-DS support in itself.


> I can disable "avahi-daemon" or disable it's DBus
> interface which will stop this,

This seems to prove that it is more related to Avahi
than to the DNS-DS support in CUPS.


> but I'd be more satisfied if I could
> configure this directly.

I am afraid - I do not know how to configure Avahi so that it
may ignore certain kind of DNS-SD "printer" information.


> It's also not related to "cups-browsed"

Because "cups-browsed" is not for DNS-SD
but for the traditional "CUPS Browsing" method.


> a) does cups (version 1.7.2 as in Linux Min 17.2), without the
> browsed-daemon, have the feature of searching and including Avahi-based
> printers and adding them dynamically to the list? I checked the source
> of "dnssd" and "mdns" backends, they utilize Avahi, but removing them
> doesn't change anything

CUPS backends are meant for sending print jobs (or printing data)
to a recipient.

CUPS backends for sending printing data via network are
also meant for discovery of network printer devices that
is useful to set up a print queue for a network printer device.

But CUPS backends are not meant for the daily-usage discovery
of available ready-to-use "printer" objects in the network
whereto an application can submit a print job.

For example a raw network printer device is ofter not 
a ready-to-use "printer" object whereto an application
can submit a print job because often for a raw network printer
device one must set up a print queue with a matching driver
and then that print queue is a ready-to-use "printer" object
whereto an application can submit a print job.


> b) Is there any possibility to ask cups who actually added the printer
> to the list? I.e., if some Mint-Specific daemon caused the problem -
> could I ask cups to tell me the process or script etc. that added the
> printer?

I am afraid - I cannot answer this question because
do not know the internals.


Kind Regards
Johannes Meixner
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