I have a SCSI CDROM drive (NEC 466) that apparently had a dirty lens.
The result was that when I attempted to read from it, at some point my
system (SuSE Linux 6.2 with kernel 2.2.13) would freeze totally, with
both mouse and keyboard dead. I was able to get this behavior, among
other ways, by logging in as root (not within X) and typing
dd if=/dev/scd0 of=/dev/null
The drive light would flash for a little bit and then go out. The
machine was then fully hung; even CapsLock had no effect (that's my
usual test for a hung keyboard). Only a hard reboot would restart
it. Interestingly, if I mounted the drive and then attempted to read
from it, I would encounter the same problem -- but then I would be
able to eject the disk, which normally I can't do with a mounted
drive.
I was able to get the drive running again by using a cleaning CDROM in
it, in audio mode.
So what's the problem, you may ask?
The problem is that although a malfunctioning drive certainly can't be
expected to yield data it can't read, the malfunction should not
freeze the system entirely; it should just produce some kind of error
message. Fortunately I'm not running a system in a critical
environment; but if I was, this kind of misbehavior would be a serious
hazard. What's needed, I think, is some kind of time-out test; if the
test times out, then the operation is cleanly aborted.
Paul Abrahams
[EMAIL PROTECTED]
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