diff --git a/Cargo.toml b/Cargo.toml
index b15bd3b..4d50c95 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,7 +15,7 @@ futures = "0.3"
 futures-util = "0.3"
 futures-signals = "0.3"
 
-slog = "2.5"
+slog = { version = "2.5", features = ["max_level_trace"] }
 slog-term = "2.5"
 slog-async = "2.4"
 
diff --git a/schema/api.capnp b/schema/api.capnp
index 6f64c24..ed09a14 100644
--- a/schema/api.capnp
+++ b/schema/api.capnp
@@ -49,10 +49,11 @@ struct UUID {
     # paramount that you are consistent when encoding and decoding this type.
     #
     # Consider using this algorithm for assembling the 128-bit integer:
-    #   uint128_t uuid = (uuid1 << 64) + uuid0;
+    # (assuming ISO9899:2018 shifting & casting rules)
+    #   uint128_t num = (uuid1 << 64) + uuid0;
     # And then respectively this code for deconstructing it:
-    #   uint64_t uuid0 = (uint64_t num);
-    #   uint64_t uuid1 = (uint64_t (num >> 64));
+    #   uint64_t uuid0 = (uint64_t) num;
+    #   uint64_t uuid1 = (uint64_t) (num >> 64);
 
     uuid0 @0 :UInt64;
     uuid1 @1 :UInt64;
@@ -63,19 +64,19 @@ interface Machines {
         setBlocked @0 ( blocked :Bool ) -> ();
         # Block or Unblock the machine. A blocked machine can not be used.
 
-        return @1 () -> ();
+        forceReturn @1 () -> ();
         # Forcefully marking a machine as `returned` — i.e. not used.
     }
 
-    interface Return {
+    interface GiveBack {
         # The only way of getting a `return` interface is by successfully calling `use`. This means
         # only the user that marked a machine as `used` can return it again. (Baring force override)
-        return @0 () -> ();
+        giveback @0 () -> ();
     }
 
     manage @0 ( uuid :UUID ) -> ( manage :Manage );
 
-    use @1 ( uuid :UUID ) -> ( return :Return );
+    use @1 ( uuid :UUID ) -> ( giveback :GiveBack );
     # Use a machine, identified by its UUID. If the caller is allowed to and the machine is
     # available to being used a `return` Capability will be returned — the person using a machine is
     # after all the only person that can return the machine after use.
diff --git a/src/machine.rs b/src/machine.rs
index edd6d90..2782adf 100644
--- a/src/machine.rs
+++ b/src/machine.rs
@@ -86,8 +86,29 @@ impl api::machines::Server for Machines {
 
         let mdb = self.mdb.lock_ref();
         if let Some(m) = mdb.get(&uuid) {
-            trace!(self.log, "Granted use on machine {}", uuid);
-            Promise::ok(())
+            match m.status {
+                Status::Free => {
+                    trace!(self.log, "Granted use on machine {}", uuid);
+
+                    let mut b = results.get();
+
+                    let gb = api::machines::give_back::ToClient::new(
+                            GiveBack::new(self.log.new(o!()), uuid, self.mdb.clone())
+                        ).into_client::<Server>();
+
+                    b.set_giveback(gb);
+
+                    Promise::ok(())
+                },
+                Status::Occupied => {
+                    info!(self.log, "Attempted use on an occupied machine {}", uuid);
+                    Promise::err(Error::failed("Machine is occupied".to_string()))
+                },
+                Status::Blocked => {
+                    info!(self.log, "Attempted use on a blocked machine {}", uuid);
+                    Promise::err(Error::failed("Machine is blocked".to_string()))
+                }
+            }
         } else {
             info!(self.log, "Attempted use on invalid machine {}", uuid);
             Promise::err(Error::failed("No such machine".to_string()))
@@ -95,6 +116,36 @@ impl api::machines::Server for Machines {
     }
 }
 
+pub struct GiveBack {
+    log: Logger,
+    mdb: Mutable<MachineDB>,
+    uuid: Uuid,
+}
+impl GiveBack {
+    pub fn new(log: Logger, uuid: Uuid, mdb: Mutable<MachineDB>) -> Self {
+        trace!(log, "Giveback initialized for {}", uuid);
+        Self { log, mdb, uuid }
+    }
+}
+
+impl api::machines::give_back::Server for GiveBack {
+    fn giveback(&mut self,
+        _params: api::machines::give_back::GivebackParams,
+        _results: api::machines::give_back::GivebackResults)
+        -> Promise<(), Error>
+    {
+        trace!(log, "Returning {}...", uuid);
+        let mut mdb = self.mdb.lock_mut();
+        if let Some(m) = mdb.get_mut(&self.uuid) {
+            m.status = Status::Free;
+        } else {
+            warn!(self.log, "A giveback was issued for a unknown machine {}", self.uuid);
+        }
+
+        Promise::ok(())
+    }
+}
+
 // FIXME: Test this exhaustively!
 fn uuid_from_api(uuid: api::u_u_i_d::Reader) -> Uuid {
     let uuid0 = uuid.get_uuid0() as u128;
diff --git a/src/main.rs b/src/main.rs
index 81c4246..58a104d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -58,16 +58,22 @@ fn main() {
     let permlog = log.new(o!());
     let machlog = log.new(o!());
 
+    machine::save(&c2, &m2.lock_ref()).expect("MachineDB save");
+
     let spawner = exec.spawner();
     let result: Result<(), Box<dyn std::error::Error>> = exec.run_until(async move {
         let listener = async_std::net::TcpListener::bind(&addr).await?;
         let mut incoming = listener.incoming();
         while let Some(socket) = incoming.next().await {
             let socket = socket?;
+            trace!(log, "New connection from {:?}", socket.peer_addr());
             // TODO: Prettify session handling
             let auth = auth::Authentication::new(authp.clone());
+            trace!(log, "Init auth");
             let perm = access::Permissions::new(permlog.clone(), enf.clone(), auth.clone());
+            trace!(log, "Init perm");
             let mach = machine::Machines::new(machlog.clone(), m.clone(), perm.clone());
+            trace!(log, "Init mach");
 
             let rpc_system = api::process_socket(auth, perm, mach, socket);
             spawner.spawn_local_obj(
@@ -77,5 +83,4 @@ fn main() {
     });
     result.expect("main");
 
-    machine::save(&c2, &m2.lock_ref()).expect("MachineDB save");
 }