linux readahead bug is back

Andre Robatino andre at bwh.harvard.edu
Fri Nov 23 18:16:38 UTC 2007


Alan Cox wrote:
> On Fri, 23 Nov 2007 02:04:03 -0500 (EST)
> "D. Hugh Redelmeier" <hugh at mimosa.com> wrote:
>
>   
>> | From andre at bwh.harvard.edu 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.
>>     
>
> It was fixed at least for all the drives we could test. Fedora 7 and 8
> use libata which uses the SCSI layer for ATAPI. The SCSI layer correctly
> understands partially successful write returns.
>
> If you could file a bug and include the info on the drive and firmware
> that would be handy.
>
> The old IDE layer had problems when reading disks raw it would get near
> the end (which isn't precisely defined for CD-R/CD-RW etc). When it asked
> for 64K and got back 32K it couldn't cope. The SCSI layer based libata is
> quite happy in that situation and will only error if the user then tries
> to read beyond the 32K (or whatever) it actually got.
>
> Alan
>
>   
https://bugzilla.redhat.com/show_bug.cgi?id=397141
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