Читать «Энциклопедия разработчика модулей ядра Linux» онлайн - страница 8

 * (assuming 32 bit integers - up to 10 digits
 * with the minus sign) is less than BUF_LEN, which
 * 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 ***************************** */