kernel: comment queue interface

kernel/src/common/queue.rs

@@ -1,10 +1,19 @@
 //! Interface for queue structure.
 
 pub trait Queue<T> {
+    /// Returns true if there are any items in the queue, false otherwise.
     fn has_elements(&self) -> bool;
+
+    /// Returns true if the queue is full, false otherwise.
     fn is_full(&self) -> bool;
+
+    /// Returns how many elements are in the queue.
     fn len(&self) -> usize;
+
+    /// Add a new element to the back of the queue.
     fn enqueue(&mut self, val: T) -> bool;
+
+    /// Remove the element from the front of the queue.
     fn dequeue(&mut self) -> Option<T>;
 
     /// Remove all elements from the ring buffer.