diff --git a/src/c_interface.rs b/src/c_interface.rs
new file mode 100644
index 0000000..0b235fe
--- /dev/null
+++ b/src/c_interface.rs
@@ -0,0 +1,70 @@
+//! C Interfaces for ucore
+
+/// Abstract low-level file.
+///
+/// Match struct `inode` in ucore `kern/fs/vfs/inode.h`
+#[repr(C)]
+struct INode {
+    // TODO: full the struct
+}
+
+/// A buffer Rd/Wr status record
+///
+/// Match struct `iobuf` in ucore `kern/fs/iobuf.h`
+#[repr(C)]
+struct IoBuf {
+    /// the base addr of buffer (used for Rd/Wr)
+    base: *mut u8,
+    /// current Rd/Wr position in buffer, will have been incremented by the amount transferred
+    offset: i32,
+    /// the length of buffer  (used for Rd/Wr)
+    len: u32,
+    /// current resident length need to Rd/Wr, will have been decremented by the amount transferred.
+    resident: u32,
+}
+
+/// Information about a file
+///
+/// Match struct `stat` in ucore `libs/stat.h`
+#[repr(C)]
+struct Stat {
+    /// protection mode and file type
+    mode: u32,
+    /// number of hard links
+    nlinks: u32,
+    /// number of blocks file is using
+    blocks: u32,
+    /// file size (bytes)
+    size: u32,
+}
+
+const S_IFMT : u32 = 070000;          // mask for type of file
+const S_IFREG: u32 = 010000;          // ordinary regular file
+const S_IFDIR: u32 = 020000;          // directory
+const S_IFLNK: u32 = 030000;          // symbolic link
+const S_IFCHR: u32 = 040000;          // character device
+const S_IFBLK: u32 = 050000;          // block device
+
+/// Abstract operations on a inode.
+///
+/// Match struct `inode_ops` in ucore `kern/fs/vfs/inode.h`
+// TODO: Append docs from ucore
+#[repr(C)]
+struct INodeOps {
+    magic: u64,
+    open: extern fn(*mut INode, flags: u32) -> i32,
+    close: extern fn(*mut INode) -> i32,
+    read: extern fn(*mut INode, *mut IoBuf) -> i32,
+    write: extern fn(*mut INode, *mut IoBuf) -> i32,
+    fstat: extern fn(*mut INode, *mut Stat) -> i32,
+    fsync: extern fn(*mut INode) -> i32,
+    namefile: extern fn(*mut INode, *mut IoBuf) -> i32,
+    getdirentry: extern fn(*mut INode, *mut IoBuf) -> i32,
+    reclaim: extern fn(*mut INode) -> i32,
+    gettype: extern fn(*mut INode, type_store: *mut u32) -> i32,
+    tryseek: extern fn(*mut INode, pos: i32) -> i32,
+    truncate: extern fn(*mut INode, len: i32) -> i32,
+    create: extern fn(*mut INode, name: *const u8, excl: bool, inode_store: *mut *mut INode) -> i32,
+    lookup: extern fn(*mut INode, path: *mut u8, inode_store: *mut *mut INode) -> i32,
+    ioctl: extern fn(*mut INode, op: i32, data: *mut u8) -> i32,
+}
\ No newline at end of file
diff --git a/src/dirty.rs b/src/dirty.rs
index 667c9b7..8e7eab9 100644
--- a/src/dirty.rs
+++ b/src/dirty.rs
@@ -45,3 +45,10 @@ impl<T> DerefMut for Dirty<T> {
     }
 }
 
+impl<T> Drop for Dirty<T> {
+    /// Guard it is not dirty when dropping
+    fn drop(&mut self) {
+        assert!(!self.dirty, "data dirty when dropping");
+    }
+}
+
diff --git a/src/lib.rs b/src/lib.rs
index c0735cf..bb5692b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,5 +13,6 @@ mod dirty;
 mod vfs;
 mod sfs;
 mod structs;
+mod c_interface;
 #[cfg(test)]
 mod tests;
\ No newline at end of file
diff --git a/src/structs.rs b/src/structs.rs
index 7b4dca3..1bd5927 100644
--- a/src/structs.rs
+++ b/src/structs.rs
@@ -1,3 +1,5 @@
+//! On-disk structures in SFS
+
 use core::slice;
 use core::mem::size_of_val;