Retrieves string from user space with alternative warning string
user_string2_n_warn:string(addr:long,n:long,warn_msg:string)
addr
the user space address to retrieve the string from
n
the maximum length of the string (if not null terminated)
warn_msg
the warning message to return when data isn't available
Returns up to n characters of a C string from a given user space memory address. Reports the given warning message on the rare cases when userspace data is not accessible and warns (but does not abort) about the failure.