Linux Device Drivers Development

A single value copy

When it comes to copying single and simple variables, such as char and int, but not larger data types, such as structures or arrays, the kernel offers dedicated macros in order to quickly perform the desired operation. These macros are put_user(x, ptr) and get_user(x, ptr), which are explained as follows:

• put_user(x, ptr);: This macro copies a variable from kernel space to user space. x represents the value to copy to user space, and ptr is the destination address in user space. The macro returns 0 on success, or -EFAULT on error. x must be assignable to the result of dereferencing ptr. In other words, they must have (or point to) the same type.
• get_user(x, ptr);: This macro copies a variable from user space to kernel ...