Re: [PATCH] compat: convert modes to use portable file type values

[Junio C Hamano <gitster@pobox.com>]

David Michael <fedora.dm0@gmail.com> writes:

> This is my most recent attempt at solving the problem of z/OS using
> different file type values than every other OS.  I believe it should be
> safe as long as the file type bits don't ever need to be converted back
> to their native values (and I didn't see any instances of that).
>
> I've been testing it by making commits to the same repositories on
> different operating systems and pushing those changes around, and so far
> there have been no issues.
>
> Can anyone foresee any problems with this method?

I cannot offhand comment on the last question above, but the
reliance on exact S_IFxxx bit assignment was identified as a
potential problem from very early days of Git that we have known
about but didn't have need to address on any system that mattered.

This is a long overdue issue and I am happy to see it getting
tackled.  The patch seems to be a sensible implementation of your
design decision to use the one-way conversion.

> diff --git a/compat/stat.c b/compat/stat.c
> new file mode 100644
> index 0000000..0ff1f2f
> --- /dev/null
> +++ b/compat/stat.c
> @@ -0,0 +1,49 @@
> +#define _POSIX_SOURCE
> +#include <stddef.h>    /* NULL         */
> +#include <sys/stat.h>  /* *stat, S_IS* */
> +#include <sys/types.h> /* mode_t       */
> +
> +static inline mode_t mode_native_to_git(mode_t native_mode)
> +{
> +	if (S_ISREG(native_mode))
> +		return 0100000 | (native_mode & 07777);
> +	else if (S_ISDIR(native_mode))
> +		return 0040000 | (native_mode & 07777);
> +	else if (S_ISLNK(native_mode))
> +		return 0120000 | (native_mode & 07777);
> +	else if (S_ISBLK(native_mode))
> +		return 0060000 | (native_mode & 07777);
> +	else if (S_ISCHR(native_mode))
> +		return 0020000 | (native_mode & 07777);
> +	else if (S_ISFIFO(native_mode))
> +		return 0010000 | (native_mode & 07777);
> +	else /* Non-standard type bits were given. */
> +		return native_mode & 07777;
> +}