docs: Aad docs for batch operations

docs/SUMMARY.md

@@ -10,9 +10,11 @@
   - [fs](services/fs.md)
   - [hdfs](services/hdfs.md)
   - [s3](services/s3.md)
-- [Features](features/README.md)
-  - [Decompress](features/decompress.md)
-  - [Server Side Encrypt](features/server-side-encryption.md)
+- [Examples](examples/README.md)
+  - [Walk Dir](examples/walk.md)
+  - [Remove a dir recursively](examples/remove_all.md)
+  - [Read compressed files](examples/decompress-read.md)
+  - [Enable Server Side Encrypt](examples/server-side-encryption.md)
 - [Upgrade](upgrade.md)
 
 # Reference Guide

docs/features/README.md → docs/examples/README.md

@@ -1,3 +1,3 @@
-# Features
+# Examples
 
 This section will demonstrate how to use OpenDAL provided features.

docs/features/decompress.md → docs/examples/decompress-read.md

@@ -1,4 +1,4 @@
-# Decompress
+# Read compressed files
 
 OpenDAL has native decompress support.
 

docs/examples/remove_all.md

@@ -0,0 +1,9 @@
+## Remove a dir recursively
+
+OpenDAL has native support for remove a dir recursively via [`BatchOperator`](/opendal/struct.BatchOperator.html).
+
+```rust
+op.batch().remove_all("path/to/dir").await?
+```
+
+**Use this function in cautions to avoid unexpected data loss.**

docs/features/server-side-encryption.md → docs/examples/server-side-encryption.md

@@ -1,4 +1,4 @@
-# Server Side Encryption
+# Enable Server Side Encryption
 
 OpenDAL has native support for server side encryption.
 

docs/examples/walk.md

@@ -0,0 +1,98 @@
+# Walk Dir
+
+OpenDAL has native walk dir support via [`BatchOperator`](/opendal/struct.BatchOperator.html).
+
+OpenDAL supports two ways to walk a dir:
+
+- bottom up
+- top down
+
+## Bottom up
+
+`Bottom up` will list from the most inner dirs.
+
+Given the following file tree:
+
+```text
+.
+├── dir_x/
+│   ├── dir_y/
+│   │   ├── dir_z/
+│   │   └── file_c
+│   └── file_b
+└── file_a
+```
+
+The output could be:
+
+```text
+dir_x/dir_y/dir_z/file_c
+dir_x/dir_y/dir_z/
+dir_x/dir_y/file_b
+dir_x/dir_y/
+dir_x/file_a
+dir_x/
+```
+
+Refer to [`BottomUpWalker`](/opendal/io_util/struct.BottomUpWalker.html) for more information.
+
+```rust
+let mut ds = op.batch().walk_bottom_up();
+
+while let Some(de) = ds.try_next().await? {
+    match de.mode() {
+        ObjectMode::FILE => {
+            println!("Handling file")
+        }
+        ObjectMode::DIR => {
+            println!("Handling dir like start a new list via meta.path()")
+        }
+        ObjectMode::Unknown => continue,
+    }
+}
+```
+
+## Top down
+
+`Top down` will list from the most outer dirs.
+
+Given the following file tree:
+
+```text
+.
+├── dir_x/
+│   ├── dir_y/
+│   │   ├── dir_z/
+│   │   └── file_c
+│   └── file_b
+└── file_a
+```
+
+The output could be:
+
+```text
+dir_x/
+dir_x/file_a
+dir_x/dir_y/
+dir_x/dir_y/file_b
+dir_x/dir_y/dir_z/
+dir_x/dir_y/dir_z/file_c
+```
+
+Refer to [`TopDownWalker`](/opendal/io_util/struct.TopDownWalker.html) for more information.
+
+```rust
+let mut ds = op.batch().walk_top_down();
+
+while let Some(de) = ds.try_next().await? {
+    match de.mode() {
+        ObjectMode::FILE => {
+            println!("Handling file")
+        }
+        ObjectMode::DIR => {
+            println!("Handling dir like start a new list via meta.path()")
+        }
+        ObjectMode::Unknown => continue,
+    }
+}
+```

src/io_util/walk.rs

@@ -44,7 +44,7 @@ use crate::ObjectMode;
 /// └── file_a
 /// ```
 ///
-/// WalkTopDown will output entries like:
+/// TopDownWalker will output entries like:
 ///
 /// ```txt
 /// dir_x/
@@ -139,7 +139,7 @@ impl futures::Stream for TopDownWalker {
 /// └── file_a
 /// ```
 ///
-/// WalkTopDown will output entries like:
+/// BottomUpWalker will output entries like:
 ///
 /// ```txt
 /// dir_x/dir_y/dir_z/file_c