[Bug-ddrescue] Re: Reverse mode - yeah, it really is important

[Antonio Diaz Diaz]

Jay R. Ashworth wrote:
> I've looked at that section, and while I can see how it probably supports
> your assertion, believe me when I tell you that *extracting* that assertion 
> from the writing of that section requires that one be carrying around the
> amount of Theory Of Operation knowledge about the code that you have,
> not the amount that I have.  :-)

Well, as you can read in the tutorial included in the manual:

"Ddrescue is like any other power tool. You need to understand what it 
does, and you need to understand some things about the machines it does 
those things to, in order to use it safely".


> And a quick persual of the manual doesn't suggest how one might "mark the rest
> of the drive as 'non-trimmed'" in whatever fashion will trigger the usage you
> suggest.  Could you expand?

I think this is sufficiently explained in the chapter "Logfile 
Structure" given how many people has written their own scripts to 
manipulate logfiles. But perhaps adding the following example to the 
tutorial could be useful.

First run:
  $ ddrescue -v -e0 /dev/fd0 rescued_image logfile

Which gives a logfile like the following:

# Rescue Logfile. Created by GNU ddrescue version 1.13-rc1
# current_pos  current_status
0x00000200     +
#      pos        size  status
0x00000000  0x00005000  +
0x00005000  0x00000200  -
0x00005200  0x0001B000  *
0x00020200  0x00147E00  ?


Then edit the last line in the logfile replacing the "?" with a "*" and run:
  $ ddrescue -v -n /dev/fd0 rescued_image logfile

Which gives a logfile like the following:

# Rescue Logfile. Created by GNU ddrescue version 1.13-rc1
# current_pos  current_status
0x00005E00     +
#      pos        size  status
0x00000000  0x00005000  +
0x00005000  0x00000200  -
0x00005200  0x00000C00  /
0x00005E00  0x00000200  -
0x00006000  0x00162000  +


I doubt adding an option to automate this procedure is worth the hassle 
given how slow is reading backwards and how rare is a drive with a 
single, centered, and drive-blocking error.


Regards,
Antonio.