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

From: Andy Lutomirski
Date: Thu Aug 01 2013 - 21:51:58 EST

This test program:

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

#define __O_TMPFILE 020000000
#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.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/