Re: [Bug-ddrescue] ddrescue bug with overwriting the mapfile

[Scott Dwyer]

On 1/8/2019 11:44 AM, Antonio Diaz Diaz wrote:
> Hi Joe,
>
> Joe Kickman wrote:
> > Sometimes while rescuing I see the situation of hanging PC. If the
> > hang happens at the moment of rewriting the log/map file - it gets
> > size of 0
> > [...]
> > I propose to first rename the log, adding .bak at the end, flush file
> > buffer to disk (sync) and then write the new log file from memory to
> > disk, thus always having a recent backup.
>
> Thank you for reporting this.
>
> I'll implement some backup scheme similar to what you propose as soon 
> as possible. Maybe it should be controlled by an option and disabled 
> by default, given that the current method is more efficient and seems 
> to be safe enough (no complaints in 14 years).
I will break down and say this. The reason I did my implementation is 
BECAUSE of some reports of issues where the ddrescue log was corrupt 
after something like a computer lockup or power loss. Maybe you did not 
receive direct complaints, but the issue has been there. The log backup 
option should be default with the option to disable it. My 
implementation may not be the ideal way (after reading Ketil's message I 
may even update my method), but it has been proven to work. A proven 
instance: after a user had an unexpected power loss during a recovery, 
the log file was incomplete and corrupt, but the backup log was good, 
verified by my examining of both files.

Regards,
Scott