add some userful demo

demo/tioccons.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <fcntl.h>
+
+int main(int argc, char *argv[]) {
+	int fd;
+	if (argc < 2) {
+		fprintf(stderr, "usage: %s /dev/ttyX\n", argv[0]);
+		exit(EXIT_FAILURE);
+	}
+	fd = open(argv[1], O_RDWR);
+	if (fd < 0) {
+		perror("open");
+		exit(EXIT_FAILURE);
+	}
+	ioctl(fd, TIOCCONS);
+	close(fd);
+	exit(EXIT_SUCCESS);
+}