Only allow directory reads at the root level

src/main.rs

@@ -25,7 +25,15 @@ impl fs_rpc::Server for Serv {
         Ok((Some(device_pid), fd))
     }
 
-    fn open_dir(&self, _path: &std::path::Path, _mount_id: u64) -> Result<(Option<u64>, u64), Errno> {
+    fn open_dir(&self, path: &std::path::Path, _mount_id: u64) -> Result<(Option<u64>, u64), Errno> {
+        let path = path.to_str().ok_or(Errno::EINVALDAT)?;
+        if !path.is_empty() {
+            if self.devices.read().contains_key(path) {
+                return Err(Errno::ENOTDIR);
+            } else {
+                return Err(Errno::ENOENT);
+            }
+        }
         let entries = self.devices.read().keys().cloned().collect::<Vec<_>>();
         self.dirs
             .write()