Man page 9 : copy_to_user

copy_to_user - Copy a block of data into user space.

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

to
    Destination address, in user space.

from
    Source address, in kernel space.

n
    Number of bytes to copy.

User context only. This function may sleep.

Copy data from kernel space to user space.

Returns number of bytes that could not be copied. On success, this will be zero.