sanitise results of stat()/lstat() on Solaris

[six809]

Solaris 11 (possibly only 11.4) can return negative values for st_atim.tv_nsec, st_mtim.tv_nsec and st_ctim.tv_nsec.

Gnulib already identifies this as an issue and works around it with stat_time_normalize(). I've adapted that function for this patch, omitting st_ctim (unused by rsync) and using only a very simple test for time_t overflow.

The feature test macros used mean this code path will be used on all Solaris builds, but this shouldn't be an issue; it would probably be safe on anything that provides tv_nsec.

[tridge]

@WayneD looks good, pending your OK

[charmitro]

Since this function is utilized solely in scenarios where #if defined __sun && defined HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC is true, it would be more straightforward to not define it when this condition is not met.

E.g.,

#if defined __sun && defined HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC
int stat_time_normalize(int result, STRUCT_STAT *st)
{
    if (result == 0) {
        long int timespec_hz = 1000000000;
        short int const ts_off[] = { offsetof (struct stat, st_atim),
                                     offsetof (struct stat, st_mtim) };
        unsigned i;
        for (i = 0; i < sizeof ts_off / sizeof *ts_off; i++) {
            struct timespec *ts = (struct timespec *)((char *) st + ts_off[i]);
            long int q = ts->tv_nsec / timespec_hz;
            long int r = ts->tv_nsec % timespec_hz;
            if (r < 0) {
                r += timespec_hz;
                q--;
            }
            ts->tv_nsec = r;
            /* Overflow is possible, as Solaris 11 stat can yield
               tv_sec == TYPE_MINIMUM (time_t) && tv_nsec == -1000000000.  */
            time_t sec = ts->tv_sec + q;
            if ((q > 0 && sec < ts->tv_sec) || (q < 0 && sec > ts->tv_sec)) {
                errno = EOVERFLOW;
                return -1;
            }
            ts->tv_sec = sec;
        }
    }
    return result;
}
#endif