change the preopen strategy again, implement more calls

crates/wasi-c2/src/dir.rs

@@ -0,0 +1,24 @@
+use std::path::PathBuf;
+
+pub trait WasiDir {}
+
+pub(crate) struct DirEntry {
+    pub(crate) flags: u32,
+    pub(crate) preopen_path: Option<PathBuf>, // precondition: PathBuf is valid unicode
+    pub(crate) dir: Box<dyn WasiDir>,
+}
+
+pub trait TableDirExt {
+    fn is_preopen(&self, fd: u32) -> bool;
+}
+
+impl TableDirExt for crate::table::Table {
+    fn is_preopen(&self, fd: u32) -> bool {
+        if self.is::<DirEntry>(fd) {
+            let dir_entry: std::cell::RefMut<DirEntry> = self.get(fd).unwrap();
+            dir_entry.preopen_path.is_some()
+        } else {
+            false
+        }
+    }
+}