function::user_ulong_warn - Retrieves an unsigned long value stored in user
the user space address to retrieve the unsigned long
Returns the unsigned long value from a given user space address. Returns zero
when user space data is not accessible and warns about the failure (but does
not error). Note that the size of the unsigned long depends on the
architecture of the current user space task (for those architectures that
support both 64/32 bit compat tasks).