[PARPORT] Re: Bug in ppa?

David Campbell (campbell@torque.net)
Tue, 19 Jan 1999 10:16:58 +0800


Does this request warant any attention?

Date sent: Mon, 18 Jan 1999 15:38:19 +0100 (MET)
From: Huba Gaspar <huba@unixoft.hu>
Subject: Bug in ppa?

> Hi David!
> I installed linux-2.2.0-pre6 on my linux box and i found a serious bug
> what caused a total hang of my machine. The procedure is reproduceable.
> I'm using a parallel cable zip drive and an atapi cd writer with scsi on
> parallel emulation?
> I unpugged the zipdrive and then with the cd writer program I did a scsi
> bus scan. It resulted a lot of
> ppa: Parallel port cable is unplugged!!
> message in syslog.

The problem is the ppa driver registers itself against the SCSI mid-level
driver at load time. The driver expects that until the driver is unloaded that
the hardware will be available. The message in syslog is trying to say "things
are not good, plug in the ZIP drive before the SCSI mid-level driver panics".

Huba admittedly dug through the code and queried whether this valid given the
fact that the drive was not mounted and hence "not in use". I believe that 99%
of the SCSI drivers under linux would suffer a similar fate if you were to
remove the controller card from the machine before unloading the driver
(theoretically it is possible to whip a PCI card out without shorting

To actually fix this problem would result in turning the ppa driver into a TSR
program that would periodically (say every 5 seconds) probe the parallel port
for ppa devices and automatically register/deregister the SCSI hosts. This
"would be nice" but the problems that this could cause would be enormous, hence
I am opening this up to debate.

David Campbell
Check http://www.torque.net/parport for all Linux parallel port solutions.

Current project list:
a) Get ZIP Plus drive back from waranty claim
b) Maintain Linux ZIP drivers (need to update docs)

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This archive was generated by hypermail 2.0b3 on Mon 18 Jan 1999 - 21:22:15 EST