Function switch_log_printf 

pub unsafe extern "C" fn switch_log_printf(
    channel: switch_text_channel_t,
    file: *const c_char,
    func: *const c_char,
    line: c_int,
    userdata: *const c_char,
    level: switch_log_level_t,
    fmt: *const c_char,
    ...
)