diff --git a/kernel/src/device/null.rs b/kernel/src/device/null.rs
index b5e9d257..69730356 100644
--- a/kernel/src/device/null.rs
+++ b/kernel/src/device/null.rs
@@ -16,6 +16,10 @@ impl Device for Null {
         // Same value with Linux
         DeviceId::new(1, 3)
     }
+
+    fn open(&self) -> Result<Option<Arc<dyn FileIo>>> {
+        Ok(Some(Arc::new(Null)))
+    }
 }
 
 impl FileIo for Null {
diff --git a/kernel/src/device/random.rs b/kernel/src/device/random.rs
index 672cd502..0065ee63 100644
--- a/kernel/src/device/random.rs
+++ b/kernel/src/device/random.rs
@@ -31,6 +31,10 @@ impl Device for Random {
         // The same value as Linux
         DeviceId::new(1, 8)
     }
+
+    fn open(&self) -> Result<Option<Arc<dyn FileIo>>> {
+        Ok(Some(Arc::new(Random)))
+    }
 }
 
 impl FileIo for Random {
diff --git a/kernel/src/device/urandom.rs b/kernel/src/device/urandom.rs
index 188e2ca7..c3b4d8aa 100644
--- a/kernel/src/device/urandom.rs
+++ b/kernel/src/device/urandom.rs
@@ -31,6 +31,10 @@ impl Device for Urandom {
         // The same value as Linux
         DeviceId::new(1, 9)
     }
+
+    fn open(&self) -> Result<Option<Arc<dyn FileIo>>> {
+        Ok(Some(Arc::new(Urandom)))
+    }
 }
 
 impl FileIo for Urandom {
diff --git a/kernel/src/device/zero.rs b/kernel/src/device/zero.rs
index 51449ead..bd038eda 100644
--- a/kernel/src/device/zero.rs
+++ b/kernel/src/device/zero.rs
@@ -16,6 +16,10 @@ impl Device for Zero {
         // Same value with Linux
         DeviceId::new(1, 5)
     }
+
+    fn open(&self) -> Result<Option<Arc<dyn FileIo>>> {
+        Ok(Some(Arc::new(Zero)))
+    }
 }
 
 impl FileIo for Zero {
diff --git a/kernel/src/fs/inode_handle/mod.rs b/kernel/src/fs/inode_handle/mod.rs
index 10af3e26..d06d1e84 100644
--- a/kernel/src/fs/inode_handle/mod.rs
+++ b/kernel/src/fs/inode_handle/mod.rs
@@ -98,12 +98,13 @@ impl InodeHandle_ {
             todo!("support write_at for FileIo");
         }
 
-        if self.status_flags().contains(StatusFlags::O_APPEND) {
+        let status_flags = self.status_flags();
+        if status_flags.contains(StatusFlags::O_APPEND) {
             // If the file has the O_APPEND flag, the offset is ignored
             offset = self.dentry.size();
         }
 
-        if self.status_flags().contains(StatusFlags::O_DIRECT) {
+        if status_flags.contains(StatusFlags::O_DIRECT) {
             self.dentry.inode().write_direct_at(offset, reader)
         } else {
             self.dentry.inode().write_at(offset, reader)