centos man page for _copy_from_user

_COPY_FROM_USER(9)					    Memory Management in Linux						_COPY_FROM_USER(9)

NAME
       _copy_from_user - Copy a block of data from user space.

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

ARGUMENTS
       to
	   Destination address, in kernel space.

       from
	   Source address, in user space.

       n
	   Number of bytes to copy.

CONTEXT
       User context only. This function may sleep.

DESCRIPTION
       Copy data from user space to kernel space.

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

       If some data could not be copied, this function will pad the copied data to the requested size using zero bytes.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							_COPY_FROM_USER(9)