diff --git a/Cargo.toml b/Cargo.toml
index 08b9800..a882a5b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,6 +12,7 @@ panic = 'abort' # prevent `_Unwind_Resume` link error
 [dependencies]
 spin = "0.4"
 bit-set = { default-features = false, version = "0.5" } # default-features contains 'std'
+static_assertions = "0.2.5"
 
 [target.ucore.dependencies]
 bitflags = "1.0"
diff --git a/src/c_interface.rs b/src/c_interface.rs
index fd80ccc..8dfbac7 100644
--- a/src/c_interface.rs
+++ b/src/c_interface.rs
@@ -150,6 +150,7 @@ bitflags! {
 ///
 /// Match struct `iobuf` in ucore `kern/fs/iobuf.h`
 #[repr(C)]
+#[derive(Debug)]
 struct IoBuf {
     /// the base addr of buffer (used for Rd/Wr)
     base: *mut u8,
@@ -165,6 +166,7 @@ struct IoBuf {
 ///
 /// Match struct `stat` in ucore `libs/stat.h`
 #[repr(C)]
+#[derive(Debug)]
 struct Stat {
     /// protection mode and file type
     mode: u32,
@@ -195,7 +197,7 @@ const S_IFBLK: u32 = 050000;
 // TODO: Append docs from ucore
 #[repr(C)]
 pub struct INodeOps {
-    magic: u64,
+    magic: u32,
     open: extern fn(&mut INode, flags: u32) -> ErrorCode,
     close: extern fn(&mut INode) -> ErrorCode,
     read: extern fn(&mut INode, &mut IoBuf) -> ErrorCode,
@@ -223,7 +225,7 @@ pub enum ErrorCode {
     /// Process doesn't exist or otherwise
     BAD_PROC    = -2 ,
     /// Invalid parameter
-    INVAL       = -3 ,
+    Invalid = -3 ,
     /// Request failed due to memory shortage
     NO_MEM      = -4 ,
     /// Attempt to create a new process beyond
@@ -249,11 +251,11 @@ pub enum ErrorCode {
     /// Device/File is Busy
     BUSY        = -15,
     /// No Such File or Directory
-    NOENT       = -16,
+    NoEntry = -16,
     /// Is a Directory
     ISDIR       = -17,
     /// Not a Directory
-    NOTDIR      = -18,
+    NotDir = -18,
     /// Cross Device-Link
     XDEV        = -19,
     /// Unimplemented Feature
@@ -287,6 +289,10 @@ impl IoBuf {
         self.offset += len as i32;
         self.resident -= len as u32;
     }
+    fn write(&mut self, data: &[u8]) {
+        self.as_mut()[..data.len()].copy_from_slice(data);
+        self.skip(data.len());
+    }
 }
 
 impl vfs::Device for Device {
@@ -428,7 +434,22 @@ static INODE_OPS: INodeOps = {
         unimplemented!();
     }
     extern fn getdirentry(inode: &mut INode, buf: &mut IoBuf) -> ErrorCode {
-        unimplemented!();
+        const ENTRY_SIZE: usize = 256;
+        println!("{:#x?}", buf);
+        if inode.borrow().info().unwrap().type_ != vfs::FileType::Dir {
+            return ErrorCode::NotDir;
+        }
+        if buf.offset as usize % ENTRY_SIZE != 0 {
+            return ErrorCode::Invalid;
+        }
+        let id = buf.offset as usize / ENTRY_SIZE;
+        let names = inode.borrow().list().unwrap();
+        println!("offset = {}", buf.offset);
+        if id >= names.len() {
+            return ErrorCode::NoEntry;
+        }
+        buf.write(names[id].as_ref());
+        ErrorCode::Ok
     }
     extern fn reclaim(inode: &mut INode) -> ErrorCode {
         println!("inode.reclaim: {:?}", inode.borrow());
@@ -505,4 +526,6 @@ unsafe impl<'a> Alloc for &'a UcoreAllocator {
         cprintf!("free %d\n", layout.size());
         ucore::kfree(ptr);
     }
-}
\ No newline at end of file
+}
+
+assert_eq_size!(ops; INodeOps, [u8; 64]);
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index ed22d91..6ca8455 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,6 +13,8 @@ extern crate bit_set;
 #[cfg(feature = "ucore")]
 #[macro_use]
 extern crate bitflags;
+#[macro_use]
+extern crate static_assertions;
 
 #[cfg(not(test))]
 macro_rules! eprintln {
diff --git a/src/structs.rs b/src/structs.rs
index 8ff605b..7a08064 100644
--- a/src/structs.rs
+++ b/src/structs.rs
@@ -1,7 +1,7 @@
 //! On-disk structures in SFS
 
 use core::slice;
-use core::mem::size_of_val;
+use core::mem::{size_of_val, size_of};
 use core::fmt::{Debug, Formatter, Error};
 use alloc::str;
 
@@ -182,16 +182,7 @@ pub enum FileType {
     Invalid = 0, File = 1, Dir = 2, Link = 3,
 }
 
-#[cfg(test)]
-mod test {
-    use super::*;
-
-    #[test]
-    fn struct_size() {
-        use core::mem::size_of;
-        assert!(size_of::<SuperBlock>() <= BLKSIZE);
-        assert!(size_of::<DiskINode>() <= BLKSIZE);
-        assert!(size_of::<DiskEntry>() <= BLKSIZE);
-        assert_eq!(size_of::<IndirectBlock>(), BLKSIZE);
-    }
-}
\ No newline at end of file
+const_assert!(o1; size_of::<SuperBlock>() <= BLKSIZE);
+const_assert!(o2; size_of::<DiskINode>() <= BLKSIZE);
+const_assert!(o3; size_of::<DiskEntry>() <= BLKSIZE);
+const_assert!(o4; size_of::<IndirectBlock>() == BLKSIZE);