feat(ext4): mkdir and nested directory support

crates/servers/storage-server/src/tests/ext4.rs

@@ -413,6 +413,48 @@ fn create_with_missing_parent_fails() {
     assert!(fs.create(b"nodir/file.txt").is_none());
 }
 
+#[test]
+fn mkdir_creates_directory() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(fs.mkdir(b"subdir"));
+    let mut entries = [DirEntry::empty(); 8];
+    let count = fs.list_dir(b"/", &mut entries).unwrap();
+    assert!(entries[..count].iter().any(|e| e.name.as_bytes() == b"subdir" && e.is_dir));
+}
+
+#[test]
+fn create_file_in_subdirectory() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(fs.mkdir(b"docs"));
+    let h = fs.create(b"docs/readme").unwrap();
+    fs.write(h, b"content").unwrap();
+    fs.close(h);
+    let h = fs.open(b"docs/readme").unwrap();
+    let mut buf = [0u8; 32];
+    let n = fs.read(h, &mut buf).unwrap();
+    assert_eq!(&buf[..n], b"content");
+    fs.close(h);
+}
+
+#[test]
+fn list_subdirectory() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(fs.mkdir(b"mydir"));
+    let h1 = fs.create(b"mydir/a.txt").unwrap();
+    fs.close(h1);
+    let h2 = fs.create(b"mydir/b.txt").unwrap();
+    fs.close(h2);
+    let mut entries = [DirEntry::empty(); 8];
+    let count = fs.list_dir(b"mydir", &mut entries).unwrap();
+    assert_eq!(count, 2);
+}
+
+#[test]
+fn mkdir_nonexistent_parent_fails() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(!fs.mkdir(b"noparent/child"));
+}
+
 #[test]
 fn read_past_eof_returns_zero() {
     let mut fs = Ext4::mount(format_ext4_disk()).unwrap();