What causes "Seat deactivation is not implemented" in slint-ui/slint?

While the app runs, avoid VT switches/session lock/suspend — keep it the sole active session.

Seat deactivation is not implemented

Error message

Seat deactivation is not implemented

What it means

In the Linux KMS/DRM backend with the libseat feature, the seat's Disable callback — the signal that the session lost the seat (VT switch away, session lock, DRM master being taken elsewhere) — hits `unimplemented!()` and panics instead of disabling the seat and acknowledging with seat.disable(). Any libseat session deactivation therefore crashes the process.

Source

Thrown at internal/backends/linuxkms/calloop_backend.rs:128

                );
                crate::renderer::try_skia_then_femtovg_then_software
            }
        };

        #[cfg(feature = "libseat")]
        let seat_active = Rc::new(RefCell::new(false));

        //libseat::set_log_level(libseat::LogLevel::Debug);

        #[cfg(feature = "libseat")]
        let mut seat = {
            let seat_active = seat_active.clone();
            libseat::Seat::open(move |_seat, event| match event {
                libseat::SeatEvent::Enable => {
                    *seat_active.borrow_mut() = true;
                }
                libseat::SeatEvent::Disable => {
                    unimplemented!("Seat deactivation is not implemented");
                }
            })
            .map_err(|e| format!("Error opening session with libseat: {e}"))?
        };

        #[cfg(feature = "libseat")]
        while !(*seat_active.borrow()) {
            if seat.dispatch(5000).map_err(|e| format!("Error waiting for seat activation: {e}"))?
                == 0
            {
                return Err("Timeout while waiting to activate session".to_string().into());
            }
        }

        Ok(Backend {
            context: Default::default(),
            #[cfg(feature = "libseat")]
            seat: Rc::new(RefCell::new(seat)),

View on GitHub (pinned to a9ea814a58)

Solutions

While the app runs, avoid VT switches/session lock/suspend — keep it the sole active session.
Build or run without the libseat feature (direct DRM master path) if your deployment allows it.
Use the default winit backend on general-purpose desktop sessions instead of linuxkms.
Patch internal/backends/linuxkms/calloop_backend.rs to handle Disable (disable rendering, call seat.disable(), re-arm on Enable) instead of unimplemented!().
Track/file the upstream issue so proper seat deactivation lands.

Defensive patterns

Strategy: fallback

Prevention

Do not VT-switch, lock the session, or suspend while a linuxkms+libseat slint app is running.
Consider building without the libseat feature for single-session kiosk deployments.
Prefer the winit backend when running inside a normal desktop session.
Carry a local patch that handles SeatEvent::Disable (ack with seat.disable()) until upstream implements it.

When it happens

Trigger: Running a slint app with the linuxkms backend + libseat (e.g. SLINT_BACKEND=linuxkms on a logind-managed seat) and then switching virtual terminals (Ctrl+Alt+F2), locking the session, suspending, or letting another compositor grab DRM master.

Common situations: Kiosk/embedded fullscreen apps launched from a seat session; testing on a desktop by VT-switching away; system suspend while the slint app holds DRM master.

Related errors

AI-assisted analysis of slint-ui/slint@a9ea814a58 (2026-08-16). Data as JSON: /api/errors/9f0462dd23f7edce. Report an issue: GitHub.