diff --git a/Cargo.lock b/Cargo.lock
index 6d28fc5..a58005d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -13,9 +13,9 @@ dependencies = [
 
 [[package]]
 name = "autocfg"
-version = "1.3.0"
+version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0c4b4d0bd25bd0b74681c0ad21497610ce1b7c91b1022cd21c80c6fbdd9476b0"
+checksum = "ace50bade8e6234aa140d9a2f552bbee1db4d353f69b8217bc503490fc1a9f26"
 
 [[package]]
 name = "bitflags"
@@ -130,9 +130,9 @@ dependencies = [
 
 [[package]]
 name = "libc"
-version = "0.2.158"
+version = "0.2.159"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8adc4bb1803a324070e64a98ae98f38934d91957a99cfb3a43dcbc01bc56439"
+checksum = "561d97a539a36e26a9a5fad1ea11a3039a67714694aaa379433e580854bc3dc5"
 
 [[package]]
 name = "line_discipline"
@@ -233,9 +233,9 @@ dependencies = [
 
 [[package]]
 name = "redox_syscall"
-version = "0.5.4"
+version = "0.5.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0884ad60e090bf1345b93da0a5de8923c93884cd03f40dfcfddd3b4bee661853"
+checksum = "9b6dfecf2c74bce2466cabf93f6664d6998a69eb21e39f4207930065b27b771f"
 dependencies = [
  "bitflags",
 ]
@@ -264,8 +264,6 @@ checksum = "61697e0a1c7e512e84a621326239844a24d8207b4669b41bc18b32ea5cbf988b"
 [[package]]
 name = "serde"
 version = "1.0.210"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c8e3592472072e6e22e0a54d5904d9febf8508f65fb8552499a1abc7d1078c3a"
 dependencies = [
  "serde_derive",
 ]
@@ -273,12 +271,10 @@ dependencies = [
 [[package]]
 name = "serde_derive"
 version = "1.0.210"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "243902eda00fad750862fc144cea25caca5e20d615af0a81bee94ca738f1df1f"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.77",
+ "syn 2.0.79",
 ]
 
 [[package]]
@@ -324,9 +320,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "2.0.77"
+version = "2.0.79"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9f35bcdf61fd8e7be6caf75f429fdca8beb3ed76584befb503b1569faee373ed"
+checksum = "89132cd0bf050864e1d38dc3bbc07a0eb8e7530af26344d3d2bbbef83499f590"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/Cargo.toml b/Cargo.toml
index a0f2b16..403a0cb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,3 +11,7 @@ line_discipline = { version = "0.1.0", path = "../line_discipline" }
 parking_lot = "0.12.3"
 slab = "0.4.9"
 syslog_rpc = { version = "0.1.0", path = "../syslog/syslog_rpc" }
+
+[patch.crates-io]
+serde = { path = "../serde/serde" }
+serde_derive = { path = "../serde/serde_derive" }
diff --git a/src/main.rs b/src/main.rs
index 673830b..c0d2760 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,7 +1,7 @@
 use std::{
     borrow::Cow,
     collections::HashMap,
-    os::mikros::{ipc, syscalls},
+    os::mikros::{ipc, syscalls, Errno},
     path::{Path, PathBuf},
     sync::Arc,
 };
@@ -92,7 +92,7 @@ struct Serv {
 }
 
 impl dev_driver_rpc::Server for Serv {
-    fn open(&self, path: &Path) -> Result<u64, ()> {
+    fn open(&self, path: &Path) -> Result<u64, Errno> {
         if path == Path::new("ptmx") {
             let pty = Pty::new();
             let idx = self.ptys.write().insert(pty);
@@ -108,13 +108,13 @@ impl dev_driver_rpc::Server for Serv {
         } else if let Some(&idx) = self.slave_map.read().get(path) {
             Ok((idx + usize::MAX / 2) as u64)
         } else {
-            Err(())
+            Err(Errno::ENOENT)
         }
     }
 }
 
 impl file_rpc::Server for Serv {
-    fn read(&self, fd: u64, len: usize) -> Result<Cow<'_, [u8]>, ()> {
+    fn read(&self, fd: u64, len: usize) -> Result<Cow<'_, [u8]>, Errno> {
         if fd as usize >= usize::MAX / 2 {
             let ptys = self.ptys.read();
             let pty = &ptys[fd as usize - usize::MAX / 2];
@@ -126,7 +126,7 @@ impl file_rpc::Server for Serv {
         }
     }
 
-    fn write(&self, fd: u64, data: &[u8]) -> Result<(), ()> {
+    fn write(&self, fd: u64, data: &[u8]) -> Result<(), Errno> {
         if fd as usize >= usize::MAX / 2 {
             let ptys = self.ptys.read();
             let pty = &ptys[fd as usize - usize::MAX / 2];
@@ -140,14 +140,14 @@ impl file_rpc::Server for Serv {
         }
     }
 
-    fn close(&self, _fd: u64) {}
+    fn close(&self, _fd: u64) -> Result<(), Errno> { Ok(()) }
 
-    fn size(&self, _fd: u64) -> Option<u64> {
-        None
+    fn size(&self, _fd: u64) -> Result<u64, Errno> {
+        Err(Errno::ENOSYS)
     }
 
-    fn dup(&self, fd: u64) -> Option<u64> {
-        Some(fd)
+    fn dup(&self, fd: u64) -> Result<u64, Errno> {
+        Ok(fd)
     }
 
     fn register_poll(&self, fd: u64, events: PollEvents) -> u64 {
@@ -188,7 +188,7 @@ impl file_rpc::Server for Serv {
         self.polls.lock().remove(poll_id as usize);
     }
 
-    fn seek(&self, _fd: u64, _pos: file_rpc::SeekFrom) -> u64 { 0 }
+    fn seek(&self, _fd: u64, _pos: file_rpc::SeekFrom) -> Result<u64, Errno> { Err(Errno::ESPIPE) }
 }
 
 fn main() {