add more comments

src/main.rs

@@ -26,10 +26,11 @@ enum DiagDeviceError {
 }
 
 struct DiagDevice {
-    pub file: File,
+    file: File,
     use_mdm: i32,
 }
 
+// Triggers the diag device's debug logging mode
 fn enable_frame_readwrite(fd: i32, mode: i32) -> DiagResult<()> {
     unsafe {
         if libc::ioctl(fd, DIAG_IOCTL_SWITCH_LOGGING, mode, 0, 0, 0) < 0 {
@@ -48,6 +49,8 @@ fn enable_frame_readwrite(fd: i32, mode: i32) -> DiagResult<()> {
     Ok(())
 }
 
+// Unsure of what MDM actually stands for, but if `use_mdm` is > 0, then
+// an additional mask is included in every diag request
 fn determine_use_mdm(fd: i32) -> DiagResult<i32> {
     let use_mdm: i32 = 0;
     unsafe {
@@ -133,14 +136,20 @@ fn main() -> std::io::Result<()> {
     println!("Starting server");
     let listener = TcpListener::bind("0.0.0.0:43555")?;
 
+    // Since we only care about one client at a time, store a copy of that
+    // client's TcpStream in a mutex. This lets us write to the client from a
+    // separate thread
     let client_mutex: Arc<Mutex<Option<TcpStream>>> = Arc::new(Mutex::new(None));
 
+    // initialize the diag device and create a cloned handle to its file. this
+    // lets us perform reads and writes in separate threads. i *think* this is
+    // sound
     let mut dev_reader = DiagDevice::new().unwrap();
     let mut dev_writer = dev_reader.try_clone().unwrap();
 
+    // Spawn a thread to continuously read from the diag device, sending any
+    // messages to the client
     let client_mutex_clone = client_mutex.clone();
-    // Spawn a thread to continuously read from the diag device, sending
-    // messages to the client (if any)
     thread::spawn(move || {
         loop {
             match dev_reader.read_response() {