#include <stdio.h>
#include <err.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

#define AT_EMPTY_PATH 0x1000
#ifndef O_PATH
#define O_PATH          010000000
#endif

int main(int argc, char **argv)
{
  char buf[128];

  if (argc != 5)
    errx(1, "Usage: flinktest OLDPATH NEWPATH <normal|O_PATH> AT_EMPTY_PATH|proc");

  int flag;
  if (!strcmp(argv[3], "normal"))
    flag = O_RDONLY;
  else if (!strcmp(argv[3], "O_PATH"))
    flag = O_PATH;
  else
    errx(1, "bad open mode");

  int fd = open(argv[1], flag);
  if (fd == -1)
    err(1, "open");

  if (!strcmp(argv[4], "AT_EMPTY_PATH")) {
    if (linkat(fd, "", AT_FDCWD, argv[2], AT_EMPTY_PATH) != 0)
      err(1, "linkat");
  } else if (!strcmp(argv[4], "proc")) {
    sprintf(buf, "/proc/self/fd/%d", fd);
    if (linkat(AT_FDCWD, buf, AT_FDCWD, argv[2], AT_SYMLINK_FOLLOW) != 0)
      err(1, "linkat");
  } else {
    errx(1, "invalid mode");
  }
  return 0;
}