/*
 * helloworld_proc_module_symbol v1.1 9/10/06
 * www.embeddedlinuxinterfacing.com
 *
 * Copyright (C) 2003 by Craig Hollabaugh 
 * With prodding and assistance from Coleman Brumley 
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

/* v1.2 removed rv var and renamed MODULE_VERSION and MODULE_NAME to
 * remove compiler warnings.
 */

/* v1.1 changed the variable name buffer to page in proc_write function, 
 * use of term buffer was confusing to students.
 */ 

/*
 * helloworld_proc_module.c is based on procfs_example.c by Erik Mouw.
 * For more information, please see The Linux Kernel Procfs Guide,
 * http://kernelnewbies.org/documents/kdoc/procfs-guide/lkprocfsguide.html
 */

/* helloworld_proc_module
 * helloworld_proc_module demonstrates the use of a /proc directory entry.
 * The init function, init_helloworld, creates /proc/helloworld and
 * populates its data, read_proc, write_proc and owner fields. The exit
 * function, cleanup_helloworld, removes the /proc/helloworld entry.
 * The proc_read function, proc_read_helloworld, is called whenever
 * a file read operation occurs on /proc/helloworld. The
 * proc_write function, proc_write_helloworld, is called whenever a file
 * file write operation occurs on /proc/helloworld.
 *
 * To demonstrate read and write operations, this module uses data
 * structure called helloworld_data containing a char field called value.
 * Read and write operations on /proc/helloworld manipulate
 * helloworld_data->value. The init function sets value = 'Default'.
 */


/*
Here's the Makefile

ifneq ($(KERNELRELEASE),)
    obj-m       := helloworld_proc_module-v1.2.o
else
    KDIR        := /usr/src/linux
    PWD         := $(shell pwd)
default:
	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
endif
clean:
	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) clean

*/

/* This version of helloworld_proc_module exports a couple symbols
 * helloworld_data and helloworld_default. See helloworld_symbol_setter.c
 * for examples of how use these exported symbols.
 */

#define EXPORT_SYMTAB

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <asm/uaccess.h>

#define hwMODULE_VERSION "1.2"
#define hwMODULE_NAME "helloworld proc module"

/* this is how long our data->value char array can be */
#define HW_LEN 8

struct helloworld_data_t {
  char value[HW_LEN + 1];
};

static struct proc_dir_entry *helloworld_file;

struct helloworld_data_t helloworld_data;

void helloworld_default(void)
{
  strcpy(helloworld_data.value, "Default");
}


/* proc_read - proc_read_helloworld
 * proc_read_helloworld is the callback function that the kernel calls when
 * there's a read file operation on the /proc file (for example,
 * cat /proc/helloworld). The file's data pointer (&helloworld_data) is
 * passed in the data parameter. You first cast it to the helloworld_data_t
 * structure. This proc_read function then uses the sprintf function to
 * create a string that is pointed to by the page pointer. The function then
 * returns the length of page. Because helloworld_data->value is set to
 * "Default", the command cat /proc/helloworld should return
 * helloworld Default
 */
static int proc_read_helloworld(char *page, char **start, off_t off,
                                int count, int *eof, void *data)
{
  int len;

/* cast the void pointer of data to helloworld_data_t*/
  struct helloworld_data_t *helloworld_data=(struct helloworld_data_t *)data;

/* use sprintf to fill the page array with a string */
  len = sprintf(page, "helloworld %s\n", helloworld_data->value);

  return len;
}


/* proc_write - proc_write_helloworld
 * proc_write_helloworld is the callback function that the kernel calls 
 * when there's a write file operation on the /proc file, (for example,
 * echo test > /proc/helloworld). The file's data pointer
 * (&helloworld_data) is passed in the data parameter. You first cast it to
 * the helloworld_data_t structure. The page parameter points to the
 * incoming data. You use the copy_from_user function to copy the page 
 * contents to the data->value field. Before you do that, though, you check
 * the page length, which is stored in count to ensure that you don't
 * overrun the length of data->value. This function then returns the length
 * of the data copied.
 */
static int proc_write_helloworld(struct file *file, const char *page,
                                 unsigned long count, void *data)
{
  int len;

/* cast the void pointer of data to helloworld_data_t*/
  struct helloworld_data_t *helloworld_data=(struct helloworld_data_t *)data;

/* do a range checking, don't overflow buffers in kernel modules */
  if(count > HW_LEN)
    len = HW_LEN;
  else
    len = count;

/* use the copy_from_user function to copy page data to
 * to our helloworld_data->value */
  if(copy_from_user(helloworld_data->value, page, len)) {
    return -EFAULT;
  }

/* zero terminate helloworld_data->value */
  helloworld_data->value[len] = '\0';

  return len;
}

/* init - init_helloworld
 * init_helloworld creates the /proc/helloworld entry file and obtains its
 * pointer called helloworld_file. The helloworld_file fields, data,
 * read_proc, write_proc and owner, are filled.  init_helloworld completes
 * by writing an entry to the system log using printk.
 */
static int __init init_helloworld(void)
{
/* Create the proc entry and make it readable and writeable by all - 0666 */
  helloworld_file = create_proc_entry("helloworld", 0666, NULL);
  if(helloworld_file == NULL) {
    return -ENOMEM;
  }

/* set the default value of our data to Default. This way a read operation on
 * /proc/helloworld will return something. */
  strcpy(helloworld_data.value, "Default");

/* Set helloworld_file fields */
  helloworld_file->data = &helloworld_data;
  helloworld_file->read_proc = &proc_read_helloworld;
  helloworld_file->write_proc = &proc_write_helloworld;
  helloworld_file->owner = THIS_MODULE;

/* everything initialized */
  printk(KERN_INFO "%s %s initialized\n",hwMODULE_NAME, hwMODULE_VERSION);
  return 0;
}

/* exit - cleanup_helloworld
 * cleanup_helloworld removes the /proc file entry helloworld and
 * prints a message to the system log.
 */
static void __exit cleanup_helloworld(void)
{
  remove_proc_entry("helloworld", NULL);

  printk(KERN_INFO "%s %s removed\n", hwMODULE_NAME, hwMODULE_VERSION);
}


/* here are the compiler macros for module operation */
module_init(init_helloworld);
module_exit(cleanup_helloworld);

MODULE_AUTHOR("Craig Hollabaugh");
MODULE_DESCRIPTION("helloworld proc module");
MODULE_LICENSE("GPL");