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Re: linux kernel error reading end of cd/dvd

Wow! Someone who knows what he's talking about - I'm impressed.

> - CD lead-out position is documented to be inaccurate [with 75 blocks
> inaccuracy?]

Silly question - where/how? How do you arrive at 75?

I have observed the same problem with DVD+R burnt by Nero (different
box), reading on the box as previously stated, so I don't think it's
limited to CDs - it affects DVDs in the same manner.

> > There
> > are more blocks in a filesystem than just the files' data.
> If we're talking about ISO9660 layout prepared by mkisofs, then those
> "more blocks" are known to be insignificant and you can as well checksum
> every file instead of the whole filesystem image, can't you?

No. Checksumming only files does not checksum (all of) the filesystem's
metadata. From an efficiency viewpoint, checksumming files is out of
the question. Checksumming the disk is very fast, and independent of
the filesystem used. In the case of iso9660, checksumming files may be
slower by only a factor of two (sorry can't remember right now), for
udf and ext2 you can plain forget about it from a practical
perspective. The only fast way of doing it would be to read the whole
CD/DVD image to disk, loopmount, check files - might check the disk
itself in the first place.

> Does it
> really have to be whole image?

Yes. And it *ought* to work ;)

I ran a number of readcd -c2scan on the CD in question, and found a
varying number of errors (and that readcd kills the CPU). No errors at
12x speed, always some at 24x, it also seems to vary with system load.
None of the errors are close to the end - all are at < 347143 with a
filesystem size of 349552. None of the errors are "hard read errors".

> If you really have to
> checksum the whole image, then make sure to bypass the block buffer
> *and* provide sane block count value. A.

Obvious question ;): is there an easy way to bypass the block buffer?
What value do you call "sane" - count=N with N <= isoinfo -d? No point
in an N larger than that.

Thanks much,


Volker Kuhlmann			is possibly list0570 with the domain in header
http://volker.dnsalias.net/		Please do not CC list postings to me.

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