Re: [Bug-ddrescue] an issue with reading cd-rom discs on linux

[Cezary Sliwa]

On Fri, Jun 15, 2012 at 09:00:26PM +0200, Antonio Diaz Diaz wrote:
> Hello Cezary,
> 
> Cezary Sliwa wrote:
> >A CD-R disc written in Track-At-Once mode has two unreadable run-out
> >blocks at the end of the track. Linux seems to shrink the reported
> >length of the track when reading the last sectors of a track fails. If
> >this happens, ddrescue cannot be restarted (it reports that the input
> >file is shorter than the log data). Actually, one may reinsert the
> >disc before a restart, but imagine the disc is hardly recognizable...
> 
> Thanks for reporting this.
> 
> Is this the message ddrescue shows?:
>   "Bad logfile; last block begins past end of input file."

Yes.

> 
> 
> >It might be a good idea to allow rescuing data from a file which is
> >shorter than the log, even independently of the above issue.
> 
> Ddrescue already allows this, but only when the rest of the logfile is 
> marked as non-tried. Maybe this requirement can be loosened to "there 
> are no blocks marked as done in the rest of the logfile".


What is the purpose of such checks? One may have a partial (short)
copy of the file to rescue he wants to merge in. Done blocks are OK in
such a case. Just take care not to truncate the rescued file or the
log.

Cezary Sliwa


> 
> 
> Regards,
> Antonio.