Fedora Core 5 common issues and bugs

Peter Jones pjones at redhat.com
Wed Mar 29 17:37:40 UTC 2006


On Tue, 2006-03-28 at 17:13 -0500, Alan Cox wrote:
> On Tue, Mar 28, 2006 at 05:04:40PM -0500, Jeff Spaleta wrote:
> > Or to ask it another way... if you use ide=nodma  and mediacheck
> > succeeds when before it failed.. does that mean that you should then
> > use ide=nodma  when doing the actual install on that system?
> 
> Nope. The problem is a CD-R track looks something like this:
> 
> <track>
> [ISO fs]
> [0-150K or so of undefined]
> <end of track>
> 
> and the catalogue (track listing) contains various bits of magic, your drive
> serial number and start/end of each track. But that is imprecise.

mediacheck reads isofs, not just the table of contents.  At no time does
it perform a read(2), nor any other operation, which would result in an
access of any block after the end of the isofs.

> On the other hand the mounted isofs image has a known size so the isofs itself
> won't try and read or prefetch outside it.

I don't think that adequately explains what's going on here.  In
mediacheck, we never try to read the lead-out, much less the possibly
non-de-iced part of the disk.  At all.  Also, we see the same errors on
pressed CDs and DVDs, which IIRC do not have the less well defined
tracks that CD-Rs do.

The block layer (or below) does the bogus prefetch.  What inhibits this
behavior when you're accessing through a filesystem driver?

I think we have exactly the same problem there, and people have
witnessed accesses through the FS fail near the end of the disk with our
install media.  To me, it looks like the same behavior.

-- 
  Peter




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