test_tmpfile.c

#define _GNU_SOURCE 1

#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>

#define PATH_MAX	256

static int write_to_tmpfile(int fd)
{
	const char *buf = "My test for tmpfile method!";
	ssize_t ret;
	ssize_t len;

	len = strlen(buf);
	if (write(fd, buf, len) < 0) {
		perror("write");
		return -1;
	}

	return 0;
}

static int read_from_tmpfile(int fd)
{
	char buf[256];
	ssize_t ret;
	ssize_t len;

	len = sizeof(buf);
	while ((ret = read(fd, buf, len)) != 0) {
		printf("ret %d\n", ret);
		if (ret == -1) {
			if (errno == EINTR)
				continue;
			perror("read");
			return -1;
		}
		if (write(STDOUT_FILENO, buf, ret) < 0) {
			perror("write");
			return -1;
		}
	}

	return 0;
}

static int linkat_tmpfile(int fd)
{
	char path[PATH_MAX];
	pid_t pid;

	pid = getpid();
	snprintf(path, PATH_MAX, "/proc/%d/fd/%d", pid, fd);

	linkat(AT_FDCWD, path, AT_FDCWD, path, AT_SYMLINK_FOLLOW);

	return 0;
}

int main(int argc, char *argv[])
{
	int tmp_fd;
	int len;
	char buf[256];

	if (argc != 2) {
		fprintf(stderr, "usage: %s DirectoryPath\n", argv[0]);
	}

	if (tmp_fd = open(argv[1] , O_TMPFILE | O_WRONLY, 0660) < 0) {
		perror("error: open");
		fprintf(stderr, "make sure that whether %s is directory path\n", argv[1]);
		return tmp_fd;
	}

	printf("tmp_fd %d\n", tmp_fd );
	if (write_to_tmpfile(tmp_fd) < 0)
		goto out;

	if (read_from_tmpfile(tmp_fd) < 0)
		goto out;

	printf("A temporary file is created.\n");
	printf("Press enter key when killing this process.\n");

	//len = read(STDIN_FILENO, buf, sizeof(buf));
	//if (len < 0)
	//	perror("error: read ");

out:
	close(tmp_fd);
	return 0;
}