Man page 9 : __copy_to_user_inatomic

__copy_to_user_inatomic - Copy a block of data into user space, with less checking.

unsigned long __copy_to_user_inatomic(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.

Copy data from kernel space to user space. Caller must check the specified block with access_ok before calling this function. The caller should also make sure he pins the user space address so that we donAqt result in page fault and sleep.

Here we special-case 1, 2 and 4-byte copy_*_user invocations. On a fault we return the initial request size (1, 2 or 4), as copy_*_user should do. If a store crosses a page boundary and gets a fault, the x86 will not write anything, so this is accurate.