Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/wasi-common/src/fs/permissions.rs

@@ -0,0 +1,37 @@
+/// Representation of the various permissions on a file.
+///
+/// This corresponds to [`std::fs::Permissions`].
+///
+/// TODO: Not yet implemented.
+///
+/// [`std::fs::Permissions`]: https://doc.rust-lang.org/std/fs/struct.Permissions.html
+#[derive(Eq, PartialEq, Clone)]
+pub struct Permissions {}
+
+impl Permissions {
+    /// Returns true if these permissions describe a readonly (unwritable) file.
+    ///
+    /// This corresponds to [`std::fs::Permissions::readonly`].
+    ///
+    /// TODO: Not yet implemented.
+    ///
+    /// [`std::fs::Permissions::readonly`]: https://doc.rust-lang.org/std/fs/struct.Permissions.html#method.readonly
+    pub fn readonly(&self) -> bool {
+        unimplemented!("Permissions::readonly");
+    }
+
+    /// Modifies the readonly flag for this set of permissions.
+    ///
+    /// This corresponds to [`std::fs::Permissions::set_readonly`].
+    ///
+    /// TODO: Not yet implemented.
+    ///
+    /// [`std::fs::Permissions::set_readonly`]: https://doc.rust-lang.org/std/fs/struct.Permissions.html#method.set_readonly
+    pub fn set_readonly(&mut self, readonly: bool) {
+        unimplemented!("Permissions::set_readonly");
+    }
+}
+
+// TODO: functions from PermissionsExt?
+
+// TODO: impl Debug for Permissions