bug#25146: grep unusable on mingw - SAME_INODE woes

[Paul Eggert]

On 12/09/2016 07:30 AM, Bruno Haible wrote:
> How can we go forward from here? I would propose a gnulib module that defines
> a data structure that combines a 'struct stat' with the FILE_ID_INFO for native
> Windows, and rebase the 'same-inode' module on it.
>
> The other approach, to override mingw's 'struct stat' and stat/fstat/lstat()
> functions, would imply a performance hit to all stat calls, even those that
> don't want to access the st_ino field.
For grep's purposes a simple workaround is to have SAME_INODE always 
return 0 on MinGW, so I installed the attached patch into Gnulib. This 
isn't perfect (it means MinGW grep won't detect that the input and 
output are the same file), but it should be good enough to fix the 
glaring bugs and to conform to POSIX.

Although it might be helpful to have a fancier module that does the work 
of SAME_INODE but does it more accurately on MinGW, I'm not sure it's 
worth the hassle. A lot of code assumes that 'struct stat' suffices to 
identify files, and it would be a pain to clutter it with another struct 
of our own design that contains a 'struct stat' as a component. Even if 
we had another module like that, we'd need to keep SAME_INODE for the 
benefit of programs that cannot easily adopt the new struct.

It seems more plausible to override MinGW's struct stat and stat/etc. 
functions. To my mind it's OK to take a performance hit in the interest 
of portability. The performance hit would occur only on programs that 
need to deduce the equivalent of SAME_INODE.

0001-same-inode-port-to-MinGW.txt
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