Re: [Bug-ddrescue] Perl script to modify ddrescue log files

[Antonio Diaz Diaz]

Burkart Lingner wrote:
> I can't think of a case where I would use that, but it's nice to have 
> such a feature as long as it's easy to also set <new_types> only, e.g. 
> by leaving <old_types> blank. Do you have a scenario in mind where one 
> would change only specific block types into a new type?

Yes. "Inverting" a logfile could be achieved with the following command:

  ddrescuelog --change-types=+-,-+ logfile > new_logfile

But as you say, I want a solution suited for both simple and obscure 
cases. Here is the current description of --change-types in the manual:

`-a OLD_TYPES,NEW_TYPES'
`--change-types=OLD_TYPES,NEW_TYPES'
     Change the status of every block in the given domain from one type
     in OLD_TYPES to the corresponding type in NEW_TYPES, much like the
     `tr' command does, and write the resulting logfile to standard
     output. OLD_TYPES and NEW_TYPES are strings of block status
     characters as defined in the chapter Logfile Structure (*note
     Logfile Structure::). Blocks whose status is not in OLD_TYPES are
     left unchanged. If NEW_TYPES is shorter than OLD_TYPES the last
     type of NEW_TYPES is repeated as many times as necessary.

Would you change anything in it?


> If I understand <new_types> correctly, "--change-types=/-+,\?/-" for 
> instance would change non-split blocks (/) into non-tried ones (?), bad 
> sectors (-) into non-split blocks (/) and finished blocks (+) into bad 
> sectors (-). That would be weird.

Yes, that would be weird. But perhaps other type combinations are 
useful. :-)


> I like the idea of changing several block types at the same time, but then 
> I would expect them all to change into the same new type.

That is exactly what --change-types does when <new_types> is shorter 
than <old_types>. See description above.


> Altogether while I can't come up with any scenario where one would do 
> that, your solution is suited for both simple and obscure cases. So the 
> worst that could happen is that this advanced feature might never get used.

This is the only type-changing feature of ddrescuelog, so I guess it 
will be used by anybody needing to change types. :-)


> First, block size for ddrescue is 512 byte by default whereas it's 4096 
> byte for ddrescuelog.

You are right that both block sizes refer to different concepts of 
"blocks" (device blocks vs filesystem blocks). AFAIK there is no value 
which is a good default for them both. Hence the two different values.


> Second, both man pages mention that "numbers may be followed by a 
> multiplier". I think it would be nice to add something like "Numbers 
> without multiplier are interpreted as bytes." On top of that you may 
> wanna add "See below for multiplier specification" to the parameters 
> "-i", "-o", etc. Oh, finally one more thing: some options have a <bytes> 
> parameter and some have a <pos> parameter according to the man pages. 
> But aren't they really all of the same type that can be multiplied by 
> "k", "Ki", etc.? If so, shouldn't they all be called the same?

Man pages are generated with the "help2man" program, so option 
descriptions are necessarily short. Also, not all numbers without 
multiplier are interpreted as bytes. You may very well write 
"--max-retries=1k", meaning 1000 retries, or even "--cluster-size=1Ki", 
meaning 1024 sectors.

But you are right that positions are interpreted as bytes, so I'll 
change their name to <bytes> to made this clearer.


> Thanks for your continued effort to improve ddrescue and ddrescuelog. 
> They're both great tools.

You are welcome.


Best regards,
Antonio.