Exchanging data with user-space (2)

• A single value

• get_user(v, p); The kernel variable v gets the value pointer by the user-space pointer p
• put_user(v, p); The value pointed by the user-space pointer p is set to the contents of the kernel variable v.

• A buffer

• unsigned long copy_to_user(void __user *to, const void *from, unsigned long n);
• unsigned long copy_from_user(void *to, const void __user *from, unsigned long n);

• The return value must be checked. Zero on success, non-zero on failure. If non-zero, the convention is to return -EFAULT.