ioctl communication between kernel and user space

use block device as example:

user space program:

struct Test_info  test_info;

ioctl ( fd,  ADD,  &test_info);

driver:

1. define a function to deal with ioctl operation & assign this function 

    to struct block_device_operations

     ex: 

     define a function  test_ioctl

     struct block_device_operations test_ops;

     test_ops.ioctl = test_ioctl       

2.  define the function to deal with ioctl operation

     it will receive two important parameters.

     One is command, the other is argument.

     From out example,  the command received is ADD, the parameter received is &test_info

3.  copy data from user space to kernel space

     use copy_from_user