Re: lseek() on an iso9660 file

["H. Peter Anvin" <hpa _at_ zytor.com>]

Followup to:  <Pine.LNX.3.95.1020107091316.18091A-100000 _at_ chaos.analogic.com>
By author:    "Richard B. Johnson" <root _at_ chaos.analogic.com>
In newsgroup: linux.dev.kernel
> 
> Using Linux 2.4.1 I discovered a problem with lseek on CDROM files
> (iso9660). I just installed 2.4.17 and found the same problem.
> 
> The problem:
> 
> (1) A portion of the file, existing on a CDROM,  is read and its the
>     contents are written to an output file on writable media.
> 
> (2) The current input file-position is obtained using
>     pos = lseek(fd, 0, SEEK_CUR); The value returned is exactly
>     the expected value.
> 
> (3) The rest of the CDROM file is read and written to the output file.
> 
> (4) The file-position of the CDROM file is then set back to the saved
>     position using lseek(fd, pos, SEEK_SET); The value returned is
>     exactly the expected value.
> 
> (5) The CDROM file is then read and its contents are observed to be
>     scrambled in some strange manner in which word-length groups of
>     bytes from near the end of the file are interleaved with the
>     correct bytes. Basically, the file ends up being about twice
>     as long as the original, with every-other two-byte interval
>     being filled with bytes from near the end of the file.
> 

a) How long is the file?
b) What is the offset?
c) What particular iso9660 options (RockRidge, Joliet, zisofs...)
   does your disk use?
d) Mount options?

This seems to be a rather serious bug, so I'd like to get to the
bottom with it.

	-hpa

-- 
<hpa _at_ transmeta.com> at work, <hpa _at_ zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp _at_ zytor.com>
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