get_user() and put_user()

get_user()
get_user (x, ptr);
Arguments
x
Variable to store result.
ptr
Source address, in user space.
Context
User context only. This function may sleep.
Description
This macro copies a single simple variable from user space to kernel space. It supports simple types like char and int, but not larger data types like structures or arrays.
ptr must have pointer-to-simple-variable type, and the result of dereferencing ptr must be assignable to x without a cast.
Returns zero on success, or -EFAULT on error. On error, the variable x is set to zero.

put_user()
put_user (x, ptr);
Arguments
x
Value to copy to user space.
ptr
Destination address, in user space.
Context
User context only. This function may sleep.
Description
This macro copies a single simple value from kernel space to user space. It supports simple types like char and int, but not larger data types like structures or arrays.
ptr must have pointer-to-simple-variable type, and x must be assignable to the result of dereferencing ptr.
Returns zero on success, or -EFAULT on error.