[Bug-ddrescue] ddrescue bug with overwriting the mapfile

[Joe Kickman]

Hello. 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 :(. 
Luckily, the times that happened I had an almost recent backup copy. 40 minutes 
of work was lost. As for a 3Tb drive - it is almost nothing, that drive is 
being copied already for 3 days, now it is 90% done.
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. A similar mechanism is used by hddsuperclone, and it 
was able to recover the log some times I have seen.
And 2 people wrote to me reporting the same problem. So I've got myself to 
inform the whole community.

What do you think?