Implement basic queue type for convenience

kernel/rustkernel/src/console/uart.rs

@@ -1,7 +1,10 @@
 //! Low-level driver routines for 16550a UART.
 #![allow(non_upper_case_globals)]
 
-use crate::{console::consoleintr, proc::wakeup, sync::spinlock::Spinlock, trap::InterruptBlocker};
+use crate::{
+    console::consoleintr, proc::wakeup, queue::Queue, sync::spinlock::Spinlock,
+    trap::InterruptBlocker,
+};
 use core::ptr::addr_of;
 
 // The UART control registers.
@@ -22,8 +25,6 @@ const LSR_RX_READY: u8 = 1 << 0;
 /// THR can accept another character to send
 const LSR_TX_IDLE: u8 = 1 << 5;
 
-const UART_TX_BUF_SIZE: usize = 32;
-
 pub static UART0: Uart = Uart::new(crate::riscv::memlayout::UART0);
 
 enum Register {
@@ -61,18 +62,14 @@ impl Register {
 pub struct Uart {
     pub lock: Spinlock,
     pub base_address: usize,
-    pub buffer: [u8; UART_TX_BUF_SIZE],
-    pub queue_start: usize,
-    pub queue_end: usize,
+    pub buffer: Queue<u8>,
 }
 impl Uart {
     pub const fn new(base_address: usize) -> Uart {
         Uart {
             lock: Spinlock::new(),
             base_address,
-            buffer: [0u8; UART_TX_BUF_SIZE],
-            queue_start: 0,
-            queue_end: 0,
+            buffer: Queue::new(),
         }
     }
     /// Initialize the UART.
@@ -146,7 +143,8 @@ impl Uart {
             }
         }
 
-        while self.queue_start == self.queue_end + 1 {
+        // Sleep until there is space in the buffer.
+        while self.buffer.space_remaining() == 0 {
             unsafe {
                 guard.sleep(addr_of!(*self).cast_mut().cast());
             }
@@ -157,10 +155,7 @@ impl Uart {
         let this: &mut Uart = unsafe { &mut *addr_of!(*self).cast_mut() };
 
         // Add the byte onto the end of the queue.
-        this.buffer[this.queue_end] = b;
-        this.queue_end += 1;
-        this.queue_end %= this.buffer.len();
-
+        this.buffer.push_back(b).expect("space in the uart queue");
         this.send_buffered_bytes();
     }
     pub fn write_slice_buffered(&self, bytes: &[u8]) {
@@ -175,14 +170,6 @@ impl Uart {
         let this: &mut Uart = unsafe { &mut *addr_of!(*self).cast_mut() };
 
         loop {
-            // Ensure the indices are correct.
-            this.queue_start %= this.buffer.len();
-            this.queue_end %= this.buffer.len();
-
-            if this.queue_start == this.queue_end {
-                // The buffer is empty, we're finished sending bytes.
-                return;
-            }
             if Register::LineStatus.read(this.base_address) & LSR_TX_IDLE == 0 {
                 // The UART transmit holding register is full,
                 // so we cannot give it another byte.
@@ -191,9 +178,10 @@ impl Uart {
             }
 
             // Pop a byte from the front of the queue.
-            let b = this.buffer[this.queue_start];
-            this.queue_start += 1;
-            this.queue_start %= this.buffer.len();
+            let Some(b) = this.buffer.pop_front() else {
+                // The buffer is empty, we're finished sending bytes.
+                return;
+            };
 
             // Maybe uartputc() is waiting for space in the buffer.
             unsafe {

kernel/rustkernel/src/io/pipe.rs

@@ -36,6 +36,11 @@ impl Pipe {
         }
     }
 }
+impl Default for Pipe {
+    fn default() -> Pipe {
+        Pipe::new()
+    }
+}
 
 extern "C" {
     // pub fn pipealloc(a: *mut *mut File, b: *mut *mut File) -> i32;
@@ -122,6 +127,7 @@ pub unsafe extern "C" fn pipewrite(pipe: *mut Pipe, addr: u64, n: i32) -> i32 {
 }
 
 #[no_mangle]
+#[allow(clippy::while_immutable_condition)]
 pub unsafe extern "C" fn piperead(pipe: *mut Pipe, addr: u64, n: i32) -> i32 {
     let mut i = 0;
     let p = myproc();

kernel/rustkernel/src/lib.rs

@@ -13,6 +13,7 @@ pub mod fs;
 pub mod io;
 pub mod mem;
 pub mod proc;
+pub mod queue;
 pub(crate) mod riscv;
 pub mod start;
 pub mod string;

kernel/rustkernel/src/queue.rs

@@ -0,0 +1,105 @@
+use core::iter::*;
+
+pub const QUEUE_SIZE: usize = 64;
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum QueueError {
+    NoSpace,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub struct Queue<T> {
+    inner: [Option<T>; QUEUE_SIZE],
+    /// The index of the first item in the queue.
+    queue_start: usize,
+    /// The length of the queue.
+    queue_len: usize,
+}
+impl<T: Copy> Queue<T> {
+    pub const fn new() -> Queue<T> {
+        Queue {
+            inner: [None; QUEUE_SIZE],
+            queue_start: 0,
+            queue_len: 0,
+        }
+    }
+}
+impl<T> Queue<T> {
+    /// Accessor method for the length of the queue.
+    pub fn len(&self) -> usize {
+        self.queue_len
+    }
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+    /// Returns how many items can currently be added to the queue.
+    pub fn space_remaining(&self) -> usize {
+        self.inner.len() - self.len()
+    }
+    /// Returns the index of the last item in the queue.
+    fn queue_end(&self) -> usize {
+        (self.queue_start + self.queue_len - 1) % self.inner.len()
+    }
+
+    /// Removes an item from the front of the queue.
+    pub fn pop_front(&mut self) -> Option<T> {
+        let item = self.inner[self.queue_start].take();
+        if item.is_some() {
+            self.queue_start += 1;
+            self.queue_start %= self.inner.len();
+            self.queue_len -= 1;
+        }
+        item
+    }
+    /// Adds an item to the front of the queue.
+    pub fn push_front(&mut self, value: T) -> Result<(), QueueError> {
+        if self.space_remaining() == 0 {
+            return Err(QueueError::NoSpace);
+        }
+
+        if self.queue_start == 0 {
+            self.queue_start = self.inner.len() - 1;
+        } else {
+            self.queue_start -= 1;
+        }
+        self.inner[self.queue_start] = Some(value);
+        self.queue_len += 1;
+        Ok(())
+    }
+    /// Removes an item from the end of the queue.
+    pub fn pop_back(&mut self) -> Option<T> {
+        let item = self.inner[self.queue_start].take();
+        if item.is_some() {
+            self.queue_len -= 1;
+        }
+        item
+    }
+    /// Adds an item to the end of the queue.
+    pub fn push_back(&mut self, value: T) -> Result<(), QueueError> {
+        if self.space_remaining() == 0 {
+            return Err(QueueError::NoSpace);
+        }
+
+        self.queue_len += 1;
+        self.inner[self.queue_end()] = Some(value);
+        Ok(())
+    }
+}
+
+impl<T> Iterator for Queue<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.pop_front()
+    }
+}
+impl<T> DoubleEndedIterator for Queue<T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.pop_back()
+    }
+}
+impl<T> ExactSizeIterator for Queue<T> {
+    fn len(&self) -> usize {
+        self.len()
+    }
+}