I have a library that uses fstatat to open a directory, and then stat a path relative to that directory using code resembling the following:

int fd = open("/some/directory", O_DIRECTORY);
if (-1 == fd) {
   // handle error
   return;
}

struct stat st = {0};
if (-1 == fstatat(fd, "./file_in_dir", &st, AT_SYMLINK_NOFOLLOW)) {
    // handle error
}

close(fd);

I am able to enumerate the contents of the directory using fdopendir / readdir, so I know I have a valid directory file descriptor. Regardless, no matter what I try, I always get a -1 return value from fstatat (and openat) with errno == EINVAL (22).

According to the IBM documentation, fstatat can result in EINVAL when the flags are invalid. Having discovered this, I grepped the system headers for AT_SYMLINK_NOFOLLOW and found the following:

#if (_XOPEN_SOURCE >= 700) || defined(_KERNEL)
#define AT_FDCWD                (-2)    /* Use the current working
                                         * directory to determine the
                                         * beginning of relative file
                                         * paths.                       */
#define AT_EACCESS              1       /* Check access using effective
                                         * user and group ID.           */
#define AT_SYMLINK_NOFOLLOW     1       /* Do not follow symbolic links */
#define AT_SYMLINK_FOLLOW       2       /* Follow symbolic links        */
#define AT_REMOVEDIR            1       /* Remove the directory entry
                                         * specified by fd and path as
                                         * a directory, not a normal
                                         * file.                        */
#endif

Now, I may be off-base, but doesn't this seem like no matter what value you pass for flags, it is invalid because AT_REMOVEDIR is the same value as AT_EACCESS and AT_SYMLINK_NOFOLLOW? Even if that isn't the case, I still haven't made it work.

I have tried every permutation of flags, trailing slashes, no trailing slashes, dot-slash prefix, no dot-slash prefix, etc. This code works correctly on every single platform we've encountered to date, and that is not an insignificant number.

I have been trying to figure this out for many hours now, so I am resorting to asking here. Anyone out there have a clue?

------------------------------
Jeff Johnson
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