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