add simple File struct

src/file.rs

@@ -0,0 +1,29 @@
+use vfs::{INode, Result};
+use alloc::sync::Arc;
+
+pub struct File {
+    inode: Arc<INode>,
+    offset: usize,
+    readable: bool,
+    writable: bool,
+}
+
+impl File {
+    pub fn new(inode: Arc<INode>, readable: bool, writable: bool) -> Self {
+        File { inode, offset: 0, readable, writable }
+    }
+
+    pub fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
+        assert!(self.readable);
+        let len = self.inode.read_at(self.offset, buf)?;
+        self.offset += len;
+        Ok(len)
+    }
+
+    pub fn write(&mut self, buf: &[u8]) -> Result<usize> {
+        assert!(self.writable);
+        let len = self.inode.write_at(self.offset, buf)?;
+        self.offset += len;
+        Ok(len)
+    }
+}

src/lib.rs

@@ -25,6 +25,7 @@ mod util;
 mod blocked_device;
 mod vfs;
 mod sfs;
+pub mod file;
 mod structs;
 #[cfg(test)]
 mod tests;