Re: [hpoj-devel] Re: ptal-printd init script for RedHat (David Paschal)

[<pa...@rc...>]

Timothy Lee wrote:
> There's one problem I've found with ptal-printd using the initscript.
> There is another problem related to the loadable modules. The situation
> goes likes this:
> ptal-printd will start with the printer off, but if I try to
> print, it quits. After reading through the source code, it appears
> that any manner of error will cause ptal-printd to exit.
> In my opinion, error conditions should be logged, but the daemon should
> just continue to run. Otherwise the machine will be left in a broken
> state, thinking the ptal-printd subsystem is running, when in fact the
> daemon is long gone.
My fault -- sorry about that.  I'll clean up my sloppiness later.  :-)

Part of the problem was that it wasn't immediately obvious what the most
appropriate recovery was for each of the possible errors.  I suppose it's
OK to exit if an error occurs during startup, for example, failure to create
the pipe.  But there are several causes of error at runtime:
- Failure to open the pipe (possibly because somebody deleted it).
- select() fails on the open pipe (I don't know why).
- Failure to open a connection to the peripheral (such as you described above).
- Failure to write data to the peripheral.

In all four cases there is data that needs to be sent to the peripheral, so
if I fix ptal-printd so it doesn't abort, what do you think I should do with
the data?  I could just discard the data (after logging a message, of course),
or in the case where I can't open the peripheral, I could periodically retry.

Speaking of logging, I probably should use syslog, not just printf.

> My question: is the device list fixed for ieee12844.o during
> loading, or is it updated dynamically? If not, there'll definitely
> be a problem with OfficeJets that were not turned on during boot up (must
> remove modules by hand, or wait for cron to clean up autoload modules).
The device list for ieee12844pp (not ieee12844) comes from whatever was
connected and powered on when parport_probe was loaded.  So if you forgot
to turn on your peripheral before booting, then you need to unload both
ieee12844pp.o and parport_probe, then reload parport_probe and ieee12844p.o.

David