[lug] DVD drive hanging system

[Jed S. Baer]

On Sat, 13 Aug 2016 22:26:10 +0000 (UTC)
stimits at comcast.net wrote:

> One possibility to recover slightly more gracefully is via the magic
> sysrq keys. See: https://en.wikipedia.org/wiki/Magic_SysRq_key

I have a printout of those ... someplace. It's in this room, I'm sure.

Years ago, I tried to use them once, as an experiment, and got no
results. And that was back when I was building custom kernels, and I did
enable sysrq. Possibly, I should repeat the experiment some time.

> If enabled, you may be able to "alt-sysrq-s" to call sync, then
> "alt-sysrq-r" to force read-only remount.

I'm pretty sure the sync and unmount features won't do anything, because
the controller is hung.

> If you can log an OOPS someone might be
> able to debug it without the particular scratched DVD.

Don't have an OOPS condition, at least not one that presents itself. It's
just hung. I did fire up the kerneloops program. Maybe it'll find
something.

> It sounds like
> you have hit a bug in the driver. I can imagine that testing for this
> kind of corrupt data might be difficult...imagine if someone had to
> have the same DVD scratched in the same way to reproduce the problem.
> Although probably not too useful to you, you may be able to recover
> what is seen on the DVD via "dd". dd does not care about some of the
> drivers which would otherwise matter if you were reading it as a file
> system. 

Not trying to copy anything, just watching movies.

I don't think it'd require an exact duplicate DVD. But maybe the same
model DVD drive.