[PATCH 1/4] Sync getcwd with gnulib

[Florian Weimer]

* Adhemerval Zanella via Libc-alpha:

> +#if HAVE_MINIMALLY_WORKING_GETCWD
> +  /* If AT_FDCWD is not defined, the algorithm below is O(N**2) and
> +     this is much slower than the system getcwd (at least on
> +     GNU/Linux).  So trust the system getcwd's results unless they
> +     look suspicious.
> +
> +     Use the system getcwd even if we have openat support, since the
> +     system getcwd works even when a parent is unreadable, while the
> +     openat-based approach does not.
> +
> +     But on AIX 5.1..7.1, the system getcwd is not even minimally
> +     working: If the current directory name is slightly longer than
> +     PATH_MAX, it omits the first directory component and returns
> +     this wrong result with errno = 0.  */
> +
> +# undef getcwd
> +  dir = getcwd_system (buf, size);
> +  if (dir || (size && errno == ERANGE))
> +    return dir;

This conflicts with the getcwd_system implementation does not set errno.

> +  /* Solaris getcwd (NULL, 0) fails with errno == EINVAL, but it has
> +     internal magic that lets it work even if an ancestor directory is
> +     inaccessible, which is better in many cases.  So in this case try
> +     again with a buffer that's almost always big enough.  */
> +  if (errno == EINVAL && buf == NULL && size == 0)
> +    {
> +      char big_buffer[BIG_FILE_NAME_LENGTH + 1];
> +      dir = getcwd_system (big_buffer, sizeof big_buffer);
> +      if (dir)
> +        return strdup (dir);
> +    }

> +          /* When we've iterated through all directory entries without finding
> +             one with a matching d_ino, rewind the stream and consider each
> +             name again, but this time, using lstat.  This is necessary in a
> +             chroot on at least one system (glibc-2.3.6 + linux 2.6.12), where
> +             .., ../.., ../../.., etc. all had the same device number, yet the
> +             d_ino values for entries in / did not match those obtained
> +             via lstat.  */
> +          if (d == NULL && errno == 0 && use_d_ino)
> +            {
> +              use_d_ino = false;
> +              __rewinddir (dirstream);
> +              d = __readdir (dirstream);
> +            }

I'm not sure if it's worthwhile to have such code in glibc.

The generic getcwd isn't used by Hurd, right?  Would it make sense to
have a trimmed-down Linux implementation as well?

Thanks,
Florian