* 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. */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
static ssize_t device_write(struct file *file, const char *buffer, size_t length, loff_t *offset)
#else
static int device_write(struct inode *inode, struct file *file, const char *buffer, int length)
#endif
{
int i;
#ifdef DEBUG
printk("device_write(%p,%s,%d)", file, buffer, length);
#endif
for(i=0; i<length && i<BUF_LEN; i++)
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
get_user(Message[i], buffer+i);
#else
Message[i] = get_user(buffer+i);
#endif
Message_Ptr = Message;
/* Again, return the number of input characters used */
return i;
}
/* This function is called whenever a process tries to
* do an ioctl on our device file. We get two extra
* parameters (additional to the inode and file
* structures, which all device functions get): the number
* of the ioctl called and the parameter given to the ioctl function.
*
* If the ioctl is write or read/write (meaning output
* is returned to the calling process), the ioctl call
* returns the output of this function. */
int device_ioctl(struct inode *inode, struct file *file,
unsigned int ioctl_num, /* The number of the ioctl */
unsigned long ioctl_param) /* The parameter to it */
{
int i;
char *temp;
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
char ch;
#endif
/* Switch according to the ioctl called */
switch (ioctl_num) {
case IOCTL_SET_MSG:
/* Receive a pointer to a message (in user space)
* and set that to be the device's message. */
/* Get the parameter given to ioctl by the process */
temp = (char*)ioctl_param;
/* Find the length of the message */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
get_user(ch, temp);
for (i=0; ch && i<BUF_LEN; i++, temp++) get_user(ch, temp);
#else
for (i=0; get_user(temp) && i<BUF_LEN; i++, temp++) ;
#endif
/* Don't reinvent the wheel - call device_write */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
device_write(file, (char*)ioctl_param, i, 0);
#else
device_write(inode, file, (char*)ioctl_param, i);
#endif
break;
case IOCTL_GET_MSG:
/* Give the current message to the calling
* process - the parameter we got is a pointer, fill it. */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
i = device_read(file, (char*)ioctl_param, 99, 0);
#else
i = device_read(inode, file, (char*)ioctl_param, 99);
#endif
/* Warning - we assume here the buffer length is
* 100. If it's less than that we might overflow
* the buffer, causing the process to core dump.
*
* The reason we only allow up to 99 characters is
* that the NULL which terminates the string also needs room. */
/* Put a zero at the end of the buffer, so it will be properly terminated */
put_user('\0', (char*)ioctl_param+i);
break;
case IOCTL_GET_NTH_BYTE:
/* This ioctl is both input (ioctl_param) and
* output (the return value of this function) */
return Message[ioctl_param];
break;
}
return SUCCESS;
}
/* Module Declarations *************************** */
/* 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 */
device_ioctl, /* 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() {
int ret_val;
/* Register the character device (atleast try) */
ret_val = module_register_chrdev(MAJOR_NUM, DEVICE_NAME, &Fops);
/* Negative values signify an error */
if (ret_val < 0) {
printk("%s failed with %d\n", "Sorry, registering the character device ", ret_val);
return ret_val;
}
printk("%s The major device number is %d.\n", "Registeration is a success", MAJOR_NUM);
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 %s c %d 0\n", DEVICE_FILE_NAME, MAJOR_NUM);
printk ("The device file name is important, because\n");
printk ("the ioctl program assumes that's the\n");
printk ("file you'll use.\n");