O_TMPFILE and linkat(/proc/self/fd/...) on tmpfs creates a weird file

[Andy Lutomirski]

This test program:

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

#define __O_TMPFILE 020000000
#define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
#define AT_EMPTY_PATH 0x1000

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

  if (argc != 3)
    errx(1, "Usage: flinktest PATH linkat|proc");

  int fd = open(".", O_TMPFILE | O_RDWR);
  if (fd == -1)
    err(1, "O_TMPFILE");
  write(fd, "test", 4);

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


run on tmpfs results in a "weird file".   stat thinks it has "Access:
(0000/?--------) and cat says "Invalid argument".

This is on -linus from a couple minutes ago.

--Andy
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