Re: permission denied in cygwin

[Christian Franke]

Hi Antonio,

Antonio Diaz Diaz wrote:

> ...
> > This leads to the following suggestion for a ddrescue enhancement to
> > handle platform/controller/driver specific values of errno after read
> > errors:
>
> I think that mapping unknown Windows errors to EACCES, as Cygwin does, 
> is wrong. Some of those unknown errors may be fatal and should make 
> ddrescue quit. 

Source code control forensics reveals that the EACCES(S) decision was 
done in last millenium. This related comment was added in August 2000 
and persists until today: /* FIXME: what's so special about EACCESS? */:
https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/errno.cc;h=25dcf70#l113
https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/errno.cc#l184

The problem is that no errno is offered for "unspecified" errors and 
interestingly also not for "media changed". Here the current errno.h 
from the Cygwin CRT (aka "newlib", https://sourceware.org/newlib/):
https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=newlib/libc/include/sys/errno.h

A fallback is needed, see the windows error defines and Cygwin's mapping 
table:
https://sourceforge.net/p/mingw-w64/code/HEAD/tree/trunk/mingw-w64-headers/include/winerror.h
https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/local_includes/errmap.h

Any suggestion for a better fallback errno?


> For example, if Windows returns ERROR_MEDIA_CHANGED(1110) because the 
> medium really was changed, it is wrong for ddrescue to ignore the 
> error and continue reading the new device as if it were the old one.

Of course. But an actual media change situation should usually not occur 
in typical ddrescue use cases (experienced console user only, being very 
careful, exclusive access to physical machine, ...)


> Therefore I propose the following simpler change:
>
> - If ddrescue quits because of a fatal error, print also the value of 
> errno in the final message.
>
> - Add the option '--continue-on-errno=<n>[,<n>]' for systems like 
> Cygwin that map non-fatal errors to fatal errors. (Allow ignoring 
> multiple errno values).
>
> - Document that '-O, --reopen-on-error' may be needed when using 
> '--continue-on-errno'.

Great, this would help.

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.

Best regards,
Christian