linux readahead bug is back

Andre Robatino andre at
Mon Nov 26 03:05:58 UTC 2007

D. Hugh Redelmeier wrote:
> | From andre at Fri Nov 23 00:33:13 2007
> |  My father just bought a F8 DVD, but it failed the mediacheck.  It 
> | turns out that the vendor failed to apply zero-padding to the ISO file
> | before burning, and that the failure occurs about 40 KB before the end of
> | the disc, presumably due to the readahead bug having returned.  This had
> | been fixed when F7 was released, but apparently is back now in both the
> | updated F7 and F8 kernels.  Anyone know when this regression happened, and
> | if there are plans to fix it?
> My theory, based on a few samples, is that the "readahead bug" was
> never fixed.  It only manifests itself on some drives.  Older drives,
> I think.

  I should have mentioned that both I and my father are using a Sony 
DRU-120C DVD RW drive (reported by dmesg as a model Sony DW-G120A), both 
purchased about 11 months ago.  So it's not just older drives.

> I've never had trouble actually installing from a disc+drive because
> of the readahead bug.  (But a mediacheck will fail.)
> The only time that I've experienced the problem is when trying to
> access the whole raw contents of the disk.  The only important reasons
> to do so are for integrity checking or duplicating.  Perhaps you can do
> those on another drive.

  Which raises the question - is there a way to find out which 
files/packages are physically located at the end of the ISO file, where 
the readahead bug prevents reading?  It's probably only when one of 
those packages are chosen during install that a problem occurs - and 
this is much less likely with the DVD install only using a single disc, 
but knowing the specific packages would make it much easier to reproduce.
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