[cups] new print driver best practices

[Jacob Marble]

On Fri, Oct 9, 2015 at 2:07 PM, Jacob Marble <jacobmarble at google.com> wrote:

> I would like to make some things clear before finishing the design for a
> new printer driver, which requires a custom backend.
>
> cups-driverd and anything that lives in /usr/libexec/cups/driver has been
> deprecated completely.
> - Does the PPD keyword APAutoSetupTool replace [cups-driverd cat ppd-name]?
>
> - Should APAutoSetupTool be a command-line tool with zero user
> interaction, or could it gather information from the user via a GUI before
> exiting?
>
> - Is APAutoSetupTool invoked on all platforms? I ask because it's not
> under "OS X Attributes" in PPD Extensions
> <https://www.cups.org/documentation.php/doc-2.1/spec-ppd.html>.
>
> A backend filter is executed to (1) discover printers and (2) print. It
> sends interesting information through stderr, "back channels" and "side
> channels".
> - Is a backend also used for port monitoring, or should that be a separate
> binary placed in /usr/libexec/cups/monitor?
>
> - Is a port monitor how printer state is indicated when a backend isn't
> running?
>
> - How is a port monitor invoked? (how often, what triggers it, what are
> the args[], etc). The backend(7) manpage is really great; can't find
> anything for port monitoring.
>
> The PPD compiler is a nice way to generate a PPD or many PPDs with
> model-specific changes.
> - If the backend discovers a printer with device-id
> "MFG:Foo;MDL:Bar;CMD:Baz;CLS:PRINTER", is this used to find a .drv file in
> /usr/share/cups/drv/ with matching Manufacturer and Model? Are other device
> ID keys (CMD, CLS) considered at all?
>

My tests show that MFG and MDL are sufficient to select the appropriate
.drv file, and generate a PPD.

- Could a complete driver look like this (assume OS X and no extra
> filters)? Could the files all reside in /Library/Printers/Foo?
> /usr/libexec/cups/backend/foo
> /usr/libexec/cups/monitor/bar
> /usr/share/cups/drv/qux.drv
> /Library/Printers/Foo/.../bar
>
> Thanks,
>
> Jacob
>