Function hal_link 

pub unsafe extern "C" fn hal_link(
    pin_name: *const c_char,
    sig_name: *const c_char,
) -> c_int

‘hal_link()’ links a pin to a signal. ‘pin_name’ and ‘sig_name’ are strings containing the pin and signal names. If the pin is already linked to the desired signal, the command succeeds. If the pin is already linked to some other signal, it is an error. In either case, the existing connection is not modified. (Use ‘hal_unlink’ to break an existing connection.) If the signal already has other pins linked to it, they are unaffected - one signal can be linked to many pins, but a pin can be linked to only one signal. On success, hal_link() returns 0, on failure it returns a negative error code.