5.html

Linux内核编程.zip

   * is 80. BE CAREFUL NOT TO OVERFLOW BUFFERS, 
   * ESPECIALLY IN THE KERNEL!!! 
   */ 

  Message_Ptr = Message;

  /* Make sure that the module isn\'t removed while 
   * the file is open by incrementing the usage count 
   * (the number of opened references to the module, if 
   * it\'s not zero rmmod will fail)
   */
  MOD_INC_USE_COUNT;

  return SUCCESS;
}


/* This function is called when a process closes the 
 * device file. It doesn\'t have a return value in 
 * version 2.0.x because it can\'t fail (you must ALWAYS
 * be able to close a device). In version 2.2.x it is 
 * allowed to fail - but we won\'t let it. 
 */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
static int device_release(struct inode *inode, 
			  struct file *file)
#else 
static void device_release(struct inode *inode, 
			   struct file *file)
#endif
{
#ifdef DEBUG
  printk (\"device_release(%p,%p)\\n\", inode, file);
#endif
 
  /* We\'re now ready for our next caller */
  Device_Open --;

  /* Decrement the usage count, otherwise once you 
   * opened the file you\'ll never get rid of the module.
   */
  MOD_DEC_USE_COUNT;

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
  return 0;
#endif
}


/* This function is called whenever a process which 
 * have already opened the device file attempts to 
 * read from it. */


#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
static ssize_t device_read(struct file *file,
    char *buffer,    /* The buffer to fill with data */
    size_t length,   /* The length of the buffer */
    loff_t *offset)  /* Our offset in the file */
#else
static int device_read(struct inode *inode,
                       struct file *file,
    char *buffer,   /* The buffer to fill with 
		     * the data */ 
    int length)     /* The length of the buffer 
                     * (mustn\'t write beyond that!) */
#endif
{
  /* Number of bytes actually written to the buffer */
  int bytes_read = 0;

  /* If we\'re at the end of the message, return 0 
   * (which signifies end of file) */
  if (*Message_Ptr == 0)
    return 0;

  /* Actually put the data into the buffer */
  while (length && *Message_Ptr)  {

    /* Because the buffer is in the user data segment, 
     * not the kernel data segment, assignment wouldn\'t 
     * work. Instead, we have to use put_user which 
     * copies data from the kernel data segment to the 
     * user data segment. */
    put_user(*(Message_Ptr++), buffer++);


    length --;
    bytes_read ++;
  }

#ifdef DEBUG
   printk (\"Read %d bytes, %d left\\n\",
     bytes_read, length);
#endif

   /* Read functions are supposed to return the number 
    * of bytes actually inserted into the buffer */
  return bytes_read;
}




/* This function is called when somebody tries to write 
 * into our device file - unsupported in this example. */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
static ssize_t device_write(struct file *file,
    const char *buffer,    /* The buffer */
    size_t length,   /* The length of the buffer */
    loff_t *offset)  /* Our offset in the file */
#else
static int device_write(struct inode *inode,
                        struct file *file,
                        const char *buffer,
                        int length)
#endif
{
  return -EINVAL;
}




/* Module Declarations ***************************** */

/* The major device number for the device. This is 
 * global (well, static, which in this context is global
 * within this file) because it has to be accessible 
 * both for registration and for release. */
static int Major;

/* This structure will hold the functions to be 
 * called when a process does something to the device 
 * we created. Since a pointer to this structure is 
 * kept in the devices table, it can\'t be local to
 * init_module. NULL is for unimplemented functions. */


struct file_operations Fops = {
  NULL,   /* seek */
  device_read, 
  device_write,
  NULL,   /* readdir */
  NULL,   /* select */
  NULL,   /* ioctl */
  NULL,   /* mmap */
  device_open,
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
  NULL,   /* flush */
#endif
  device_release  /* a.k.a. close */
};


/* Initialize the module - Register the character device */
int init_module()
{
  /* Register the character device (atleast try) */
  Major = module_register_chrdev(0, 
                                 DEVICE_NAME,
                                 &Fops);

  /* Negative values signify an error */
  if (Major < 0) {
    printk (\"%s device failed with %d\\n\",
	    \"Sorry, registering the character\",
	    Major);
    return Major;
  }

  printk (\"%s The major device number is %d.\\n\",
          \"Registeration is a success.\",
          Major);
  printk (\"If you want to talk to the device driver,\\n\");
  printk (\"you\'ll have to create a device file. \\n\");
  printk (\"We suggest you use:\\n\");
  printk (\"mknod <name> c %d <minor>\\n\", Major);
  printk (\"You can try different minor numbers %s\",
          \"and see what happens.\\n\");

  return 0;
}


/* Cleanup - unregister the appropriate file from /proc */
void cleanup_module()
{
  int ret;

  /* Unregister the device */
  ret = module_unregister_chrdev(Major, DEVICE_NAME);
 
  /* If there\'s an error, report it */ 
  if (ret < 0)
    printk(\"Error in unregister_chrdev: %d\\n\", ret);
}</pre><hr><br><center><a href='4.html'>上一页 </a>||<a href='6.html'>下一页</a></center></div> </td>
                  </tr>
                </table>
                <p>&nbsp; </p>
                </div>
            </td>
          </tr>
        </table>
          <br>
          <table border="0" width="75%"><tr><td align="right"><a href="/"><img src="/image2/logo_bottom.gif" border="0"></a></td></tr></table>
          <hr size="1" align="center" color="#eecccc">
          <br>
        </div>
      </div>
      </td>
  </tr>
</table>
  <center><a href="http://ad.myrice.com/RealMedia/ads/click_nx.ads/goldnets.myrice.com/banner1@Bottom" target=_blanck >
<script language=JavaScript>
<!---
todayd = new Date();
var seconds = todayd.getTime();
document.write("<img src=\"http://ad.myrice.com/RealMedia/ads/adstream_nx.ads/goldnets.myrice.com/banner1@Bottom?dd=seconds\" border=0 width=468 height=60>");//-->
</script>
</a></center>
</body>
</html>