diff --git a/easy-fs/Cargo.toml b/easy-fs/Cargo.toml
index 16ffc303..8fd21501 100644
--- a/easy-fs/Cargo.toml
+++ b/easy-fs/Cargo.toml
@@ -9,4 +9,5 @@ edition = "2018"
 [dependencies]
 spin = "0.7.0"
 #lazy_static = { version = "1.4.0", features = ["spin_no_std"] }
-lazy_static = "1.4.0"
\ No newline at end of file
+lazy_static = "1.4.0"
+rand = "0.8.0"
\ No newline at end of file
diff --git a/easy-fs/src/bin/main.rs b/easy-fs/src/bin/main.rs
index c7b313c4..4a91928a 100644
--- a/easy-fs/src/bin/main.rs
+++ b/easy-fs/src/bin/main.rs
@@ -9,6 +9,7 @@ use std::fs::{File, OpenOptions};
 use std::io::{Read, Write, Seek, SeekFrom};
 use std::sync::Mutex;
 use alloc::sync::Arc;
+use rand;
 
 const BLOCK_SZ: usize = 512;
 
@@ -37,6 +38,11 @@ fn main() {
 }
 
 fn easy_fs_pack() -> std::io::Result<()> {
+    Ok(())
+}
+
+#[test]
+fn efs_test() -> std::io::Result<()> {
     let block_file = Arc::new(BlockFile(Mutex::new(
         OpenOptions::new()
             .read(true)
@@ -55,16 +61,49 @@ fn easy_fs_pack() -> std::io::Result<()> {
     for name in root_inode.ls() {
         println!("{}", name);
     }
-    {
-        let filea = root_inode.find("filea").unwrap();
-        println!("writing filea!");
-        filea.write_at(0, "Hello, world!".as_bytes());
-    }
-    {
-        let filea = root_inode.find("filea").unwrap();
-        let mut buffer = [0u8; 512];
-        let len = filea.read_at(0, &mut buffer);
-        println!("{}", core::str::from_utf8(&buffer[..len]).unwrap());
-    }
+    let filea = root_inode.find("filea").unwrap();
+    let greet_str = "Hello, world!";
+    filea.write_at(0, greet_str.as_bytes());
+    let mut buffer = [0u8; 512];
+    let len = filea.read_at(0, &mut buffer);
+    assert_eq!(
+        greet_str,
+        core::str::from_utf8(&buffer[..len]).unwrap(),
+    );
+
+    let mut random_str_test = |len: usize| {
+        filea.clear();
+        assert_eq!(
+            filea.read_at(0, &mut buffer),
+            0,
+        );
+        let mut str = String::new();
+        // random digit
+        for _ in 0..len {
+            str.push(char::from('0' as u8 + rand::random::<u8>() % 10));
+        }
+        filea.write_at(0, str.as_bytes());
+        let mut read_buffer = [0u8; 127];
+        let mut offset = 0usize;
+        let mut read_str = String::new();
+        loop {
+            let len = filea.read_at(offset, &mut read_buffer);
+            if len == 0 {
+                break;
+            }
+            offset += len;
+            read_str.push_str(
+                core::str::from_utf8(&read_buffer[..len]).unwrap()
+            );
+        }
+        assert_eq!(str, read_str);
+    };
+
+    random_str_test(4 * BLOCK_SZ);
+    random_str_test(8 * BLOCK_SZ + BLOCK_SZ / 2);
+    random_str_test(100 * BLOCK_SZ);
+    random_str_test(70 * BLOCK_SZ + BLOCK_SZ / 7);
+    random_str_test((12 + 128) * BLOCK_SZ);
+
     Ok(())
 }
\ No newline at end of file
diff --git a/easy-fs/src/bitmap.rs b/easy-fs/src/bitmap.rs
index edda5909..87f8d297 100644
--- a/easy-fs/src/bitmap.rs
+++ b/easy-fs/src/bitmap.rs
@@ -16,7 +16,7 @@ pub struct Bitmap {
 fn decomposition(mut bit: usize) -> (usize, usize, usize) {
     let block_pos = bit / BLOCK_BITS;
     bit = bit % BLOCK_BITS;
-    (block_pos, bit/64, bit % 64)
+    (block_pos, bit / 64, bit % 64)
 }
 
 impl Bitmap {
@@ -52,7 +52,7 @@ impl Bitmap {
     pub fn dealloc(&self, block_device: &Arc<dyn BlockDevice>, bit: usize) {
         let (block_pos, bits64_pos, inner_pos) = decomposition(bit);
         let mut dirty_bitmap_block: Dirty<BitmapBlock> = Dirty::new(
-            block_pos,
+            block_pos + self.start_block_id,
             0,
             block_device.clone(),
         );
diff --git a/easy-fs/src/efs.rs b/easy-fs/src/efs.rs
index 2a8af448..34c6ad82 100644
--- a/easy-fs/src/efs.rs
+++ b/easy-fs/src/efs.rs
@@ -145,7 +145,7 @@ impl EasyFileSystem {
         self.data_bitmap.alloc(&self.block_device).unwrap() as u32 + self.data_area_start_block
     }
 
-    fn dealloc_data(&mut self, block_id: u32) {
+    pub fn dealloc_data(&mut self, block_id: u32) {
         self.data_bitmap.dealloc(
             &self.block_device,
             (block_id - self.data_area_start_block) as usize
diff --git a/easy-fs/src/layout.rs b/easy-fs/src/layout.rs
index d173e0b0..99e4abc6 100644
--- a/easy-fs/src/layout.rs
+++ b/easy-fs/src/layout.rs
@@ -267,6 +267,7 @@ impl DirEntry {
     pub fn from_bytes(bytes: &DirentBytes) -> &Self {
         unsafe { &*(bytes.as_ptr() as usize as *const Self) }
     }
+    #[allow(unused)]
     pub fn from_bytes_mut(bytes: &mut DirentBytes) -> &mut Self {
         unsafe {
             &mut *(bytes.as_mut_ptr() as usize as *mut Self)
diff --git a/easy-fs/src/vfs.rs b/easy-fs/src/vfs.rs
index b544ac46..fe42adff 100644
--- a/easy-fs/src/vfs.rs
+++ b/easy-fs/src/vfs.rs
@@ -12,7 +12,6 @@ use alloc::sync::Arc;
 use alloc::string::String;
 use alloc::vec::Vec;
 use spin::{Mutex, MutexGuard};
-use crate::layout::DiskInodeType::Directory;
 
 pub struct Inode {
     inode_id: u32,
@@ -196,4 +195,15 @@ impl Inode {
             disk_inode.write_at(offset, buf, &self.block_device)
         })
     }
+
+    pub fn clear(&self) {
+        let mut fs = self.fs.lock();
+        let mut inode = self.get_disk_inode(&mut fs);
+        let data_blocks_dealloc = inode.modify(|disk_inode| {
+            disk_inode.clear_size(&self.block_device)
+        });
+        for data_block in data_blocks_dealloc.into_iter() {
+            fs.dealloc_data(data_block);
+        }
+    }
 }