strncpy_from_user — Copy a NUL terminated string from userspace.
long strncpy_from_user (char * dst, const char __user * src, long count);
dst
Destination address, in kernel space. This buffer must be at
least count bytes long.
srcSource address, in user space.
countMaximum number of bytes to copy, including the trailing NUL.
Copies a NUL-terminated string from userspace to kernel space.
On success, returns the length of the string (not including the trailing NUL).
If access to userspace fails, returns -EFAULT (some data may have been copied).
If count is smaller than the length of the string, copies count bytes
and returns count.