Add in-memory logging, retrievable from sys:log

src/log.rs

@@ -0,0 +1,35 @@
+use alloc::collections::VecDeque;
+use spin::Mutex;
+
+pub static LOG: Mutex<Option<Log>> = Mutex::new(None);
+
+pub fn init() {
+    *LOG.lock() = Some(Log::new(1024 * 1024));
+}
+
+pub struct Log {
+    data: VecDeque<u8>,
+    size: usize,
+}
+
+impl Log {
+    pub fn new(size: usize) -> Log {
+        Log {
+            data: VecDeque::with_capacity(size),
+            size: size
+        }
+    }
+
+    pub fn read(&self) -> (&[u8], &[u8]) {
+        self.data.as_slices()
+    }
+
+    pub fn write(&mut self, buf: &[u8]) {
+        for &b in buf {
+            while self.data.len() + 1 >= self.size {
+                self.data.pop_front();
+            }
+            self.data.push_back(b);
+        }
+    }
+}