centos man page for __clear_user

__CLEAR_USER(9) 					    Memory Management in Linux						   __CLEAR_USER(9)

NAME
       __clear_user - Zero a block of memory in user space, with less checking.

SYNOPSIS
       unsigned long __clear_user(void __user * to, unsigned long n);

ARGUMENTS
       to
	   Destination address, in user space.

       n
	   Number of bytes to zero.

DESCRIPTION
       Zero a block of memory in user space. Caller must check the specified block with access_ok before calling this function.

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

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							   __CLEAR_USER(9)