Re: permission denied in cygwin

[Antonio Diaz Diaz]

Christian Franke wrote:
> The problem is that no errno is offered for "unspecified" errors

IMHO the problem is the existence of "unspecified" errors. Ddrescue needs 
that the system returns 2 different kinds of errors: non-fatal (temporary or 
affecting just a sector, for example) and fatal (permanent, like EACCES 
"Permission denied").

If the system returns a fatal error code for a non-fatal error, ddrescue 
quits prematurely.

If the system returns a non-fatal error code for a fatal error, ddrescue 
marks the rest of the drive as "bad-sector" and rescues nothing.

> and interestingly also not for "media changed".

Maybe ESTALE could be used for "media changed".

> Any suggestion for a better fallback errno?

Once the system mixes fatal and non-fatal errors (for example by returning 
ERROR_MEDIA_CHANGED instead of EIO) any mapping will make ddrescue behave 
incorrectly one way or the other.

In addition to all this, option '-O, --reopen-on-error' only has effect 
during the copying phase, when data are copied in large blocks. Therefore 
the proposed '--continue-on-errno' would make ddrescue behave incorrectly 
during trimming, scraping, and retrying.

> > Therefore I propose the following simpler change:
> > [...]
> Great, this would help.

OK. I'll release a test version as soon as I have it implemented.

> For diagnostics of possible other "interesting" behavior, it would also
> be helpful to see an errno if interpreted as non-fatal but with
> unexpected value, e.g. different from EIO.

The problem is to find a way for ddrescue to show such errno values, as 
there may be thousands of failed reads per second. (Maybe adding an errno 
field to the output of '--log-reads').

Best regards,
Antonio.