Add LaTeX script and sample code

examples/chardev.h

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+/*
+ *  chardev2.h - the header file with the ioctl definitions.
+ *
+ *  The declarations here have to be in a header file, because
+ *  they need to be known both to the kernel module
+ *  (in chardev.c) and the process calling ioctl (ioctl.c)
+ */
+
+#ifndef CHARDEV_H
+#define CHARDEV_H
+
+#include <linux/ioctl.h>
+
+/*
+ * The major device number. We can't rely on dynamic
+ * registration any more, because ioctls need to know
+ * it.
+ */
+#define MAJOR_NUM 100
+
+/*
+ * Set the message of the device driver
+ */
+#define IOCTL_SET_MSG _IOW(MAJOR_NUM, 0, char *)
+/*
+ * _IOW means that we're creating an ioctl command
+ * number for passing information from a user process
+ * to the kernel module.
+ *
+ * The first arguments, MAJOR_NUM, is the major device
+ * number we're using.
+ *
+ * The second argument is the number of the command
+ * (there could be several with different meanings).
+ *
+ * The third argument is the type we want to get from
+ * the process to the kernel.
+ */
+
+/*
+ * Get the message of the device driver
+ */
+#define IOCTL_GET_MSG _IOR(MAJOR_NUM, 1, char *)
+/*
+ * This IOCTL is used for output, to get the message
+ * of the device driver. However, we still need the
+ * buffer to place the message in to be input,
+ * as it is allocated by the process.
+ */
+
+/*
+ * Get the n'th byte of the message
+ */
+#define IOCTL_GET_NTH_BYTE _IOWR(MAJOR_NUM, 2, int)
+/*
+ * The IOCTL is used for both input and output. It
+ * receives from the user a number, n, and returns
+ * Message[n].
+ */
+
+/*
+ * The name of the device file
+ */
+#define DEVICE_FILE_NAME "char_dev"
+
+#endif