#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#define bail(msg) \
	do { printf("mount_to_symlink: %s: %m\n", msg); exit(1); } while (0)

int main(int argc, char **argv)
{
	struct stat stat = {};
	char *mnt, *mnt_fdpath;
	int mnt_fd;

	if (argc != 2)
		bail("need <mount> argument");

	mnt = argv[1];

	// open mountpoint fd
	mnt_fd = open(mnt, O_PATH | O_CLOEXEC | O_NOFOLLOW);
	if (mnt_fd < 0)
		bail("open(<dst>, O_PATH|O_NOFOLLOW)");

	// get fdpaths
	asprintf(&mnt_fdpath, "/proc/self/fd/%d", mnt_fd);

	// try to mount
	umount2(mnt_fdpath, MNT_DETACH);
	printf("umount2(%s, MNT_DETACH) = %m (%d)\n", mnt, -errno);
	return 0;
}