get_entry(), as a different design from list()

src/sfs.rs

@@ -396,6 +396,14 @@ impl vfs::INode for INode {
             _ => unimplemented!(),
         }
     }
+    fn get_entry(&self,id: usize) -> vfs::Result<String> {
+        assert_eq!(self.disk_inode.type_, FileType::Dir);
+        assert!(id<self.disk_inode.blocks as usize);
+        use vfs::INode;
+        let mut entry: DiskEntry = unsafe { uninitialized() };
+        self._read_at(id as usize * BLKSIZE, entry.as_buf_mut()).unwrap();
+        Ok(String::from(entry.name.as_ref()))
+    }
     fn list(&self) -> vfs::Result<Vec<String>> {
         assert_eq!(self.disk_inode.type_, FileType::Dir);
 

src/tests.rs

@@ -62,6 +62,9 @@ fn print_root() {
 
     let files = root.borrow().list().unwrap();
     println!("{:?}", files);
+    assert_eq!(files[3],root.borrow().get_entry(3).unwrap());
+
+    sfs.sync().unwrap();
 }
 
 #[test]

src/vfs.rs

@@ -29,6 +29,9 @@ pub trait INode: Debug + Any {
     fn link(&mut self, name: &str, other:&mut INode) -> Result<()>;
     fn lookup(&self, path: &str) -> Result<INodePtr>;
     fn list(&self) -> Result<Vec<String>>;
+    /// like list()[id]
+    /// only get one item in list, often faster than list
+    fn get_entry(&self,id: usize) -> Result<String>;
 //    fn io_ctrl(&mut self, op: u32, data: &[u8]) -> Result<()>;
     fn fs(&self) -> Weak<FileSystem>;
     /// this is used to implement dynamics cast