Rewrite Stdin/Stdout

os/src/fs/mod.rs

@@ -0,0 +1,20 @@
+mod pipe;
+mod stdio;
+
+use crate::mm::UserBuffer;
+use core::any::Any;
+
+pub trait File : Any + Send + Sync {
+    fn read(&self, buf: UserBuffer) -> usize;
+    fn write(&self, buf: UserBuffer) -> usize;
+    fn as_any_ref(&self) -> &dyn Any;
+}
+
+impl dyn File {
+    pub fn downcast_ref<T: File>(&self) -> Option<&T> {
+        self.as_any_ref().downcast_ref::<T>()
+    }
+}
+
+pub use pipe::{Pipe};
+pub use stdio::{Stdin, Stdout};