fix(vdisplay/gamescope): DM-flavor-aware session takeover — stop masking Nobara's plasmalogin to death
Field report (Nobara 43 HTPC): switching the host to Steam Game Mode mid-stream permanently black-screened the box. Live-proven root cause on a Nobara repro VM: our takeover masks the box's gamescope-session-plus unit, plasmalogin's Relogin=true then fails its session Exec repeatedly and trips systemd's start limit within ~1 s — the display manager dies, and our restore verb (unmask + user start) cannot bring a seatless gamescope back. Only 'reset-failed + restart' of the DM recovers. The takeover is now display-manager-flavor-aware: - SDDM (Bazzite/SteamOS) keeps the proven mask+SIGKILL path unchanged. - plasmalogin/unknown DMs never mask: with privilege (root or an operator polkit rule scoped to the DM unit — documented) the host stops the DM for the stream and restores it with reset-failed + restart (PUNKTFUNK_RECOVER_SESSION_CMD as fallback), recorded in the persisted takeover state so a host crash still restores; without privilege the managed takeover degrades to ATTACH and mirrors the box's live Game Mode instead of destabilizing the seat. Both legs of the privileged cycle live-verified on the repro VM (headless managed session works with zero login sessions; render nodes are 0666). A loaded-but-inactive leftover instance never triggers the DM stop. Companion fixes from the same triage: - ensure_box_gamescope_mode gains the attach-only rebuild-probe guard both managed paths already had (stale post-capture-loss detection restarted the box's unit), and no longer re-modes a box that drives a physical display — attach mirrors on-glass; re-mode is the headless-box model. - Capture-loss rebuilds targeting gamescope get a 100 s budget: the 40 s budget expired inside the first 45 s Steam-cold-start launch attempt, a guaranteed single-shot failure. - A PUNKTFUNK_COMPOSITOR pin now WARNs once per capture loss when the live session no longer matches it (the pin disables session-following — the reporter's original stream-death trigger). - A managed session that took nothing over (client gamescope pin beside a live desktop) is stopped on disconnect instead of being orphaned forever. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Claude Fable 5
@@ -100,8 +100,9 @@ For Gaming Mode there are two models (pick one; the shipped default is **attach*
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- **Attach** (`PUNKTFUNK_GAMESCOPE_ATTACH=1`, the template's default) — the **box** owns its
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gamescope session on its own display, and the host attaches to whatever's live without ever
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tearing it down (a box-owned autologin session is restarted at the client's resolution on a
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mismatch). Switching Desktop ↔ Game is rock-solid.
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tearing it down (on a headless box, a box-owned autologin session is restarted at the client's
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resolution on a mismatch; with a display connected it streams at the box's own mode). Switching
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Desktop ↔ Game is rock-solid.
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- **Managed** (`PUNKTFUNK_GAMESCOPE_MANAGED=1`, and remove the attach line) — the host takes the
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box's gamescope over and relaunches it **headless** at the *client's* exact resolution and
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refresh — Game Mode on the virtual screen — restoring the box on idle.
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@@ -53,7 +53,7 @@ the full picture (and [Bazzite](/docs/bazzite) for that distro's specifics).
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| Setting | Values | Meaning |
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|---|---|---|
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| `PUNKTFUNK_GAMESCOPE_ATTACH` | `1` | **Attach** model: the box owns its gamescope session on its own display (you switch Gaming ↔ Desktop with the Steam UI); the host just captures whatever's live and never tears it down. A box-owned autologin session is restarted at the client's resolution on a mismatch; a foreign/bare gamescope streams at its own mode. |
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| `PUNKTFUNK_GAMESCOPE_ATTACH` | `1` | **Attach** model: the box owns its gamescope session on its own display (you switch Gaming ↔ Desktop with the Steam UI); the host just captures whatever's live and never tears it down. On a **headless** box the box-owned autologin session is restarted at the client's resolution on a mismatch; a box driving a physical display, and any foreign/bare gamescope, streams at its own mode. |
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| `PUNKTFUNK_GAMESCOPE_MANAGED` | `1` | **Managed** model (the default where session infra is detected): the host takes the box's gamescope over and relaunches it **headless** at the *client's* exact resolution — Game Mode on the virtual screen — restoring the box on idle. |
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| `PUNKTFUNK_GAMESCOPE_SESSION` | `steam` | The host owns a `gamescope-session-plus` (Steam) session at the client's mode (headless appliance; no physical session running). |
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| `PUNKTFUNK_GAMESCOPE_NODE` | `auto` · node id | Discover + capture a **running** gamescope's PipeWire node at a fixed mode. Do **not** combine with `SESSION`. |
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@@ -24,14 +24,42 @@ that has gamescope session infrastructure (Bazzite, SteamOS, Nobara) gets **mana
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- **Attach** (`PUNKTFUNK_GAMESCOPE_ATTACH=1`) — the **box** owns its gamescope session and decides
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Gaming vs Desktop via the normal Steam UI. Game Mode stays on the box's own (physical) display;
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the host attaches to whatever's live and never tears it down, so switching Desktop ↔ Game is
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rock-solid and disconnecting leaves the box where it was. When the session is the box's own
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autologin unit, the host restarts it at the **client's** resolution on a mismatch; a foreign or
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bare gamescope is streamed at its own mode.
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rock-solid and disconnecting leaves the box where it was. When the box is **headless** (no
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display connected) and the session is its own autologin unit, the host restarts it at the
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**client's** resolution on a mismatch; a box driving a physical display — and any foreign or
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bare gamescope — is streamed at its own mode.
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- **Managed** (the infra-detected default; force with `PUNKTFUNK_GAMESCOPE_MANAGED=1`) — the host
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takes the box's gamescope session over and relaunches it **headless** at the *client's* exact
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resolution and refresh — Game Mode runs on the virtual screen, physical displays drop out of it —
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restoring the box on idle after disconnect.
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### Nobara and other autologin display managers
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The managed takeover has to stop the box's Gaming Mode session to free Steam. How it does that
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depends on the display manager driving the autologin:
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- **SDDM** (Bazzite, SteamOS): handled automatically — no setup.
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- **plasmalogin** (Nobara) and other display managers: the host must stop the display manager
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itself for the length of the stream and restart it afterwards, which needs privilege. Allow it
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with a polkit rule (adjust the unit and user names to your box):
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```js
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// /etc/polkit-1/rules.d/49-punktfunk-dm.rules
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polkit.addRule(function(action, subject) {
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if (action.id == "org.freedesktop.systemd1.manage-units" &&
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action.lookup("unit") == "plasmalogin.service" &&
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subject.user == "YOUR_USER") {
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return polkit.Result.YES;
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}
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});
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```
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Without the rule the host degrades safely: it **attaches** to the live Gaming Mode session
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instead (Game Mode stays on the box's display, mirrored to the client) rather than risk the
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display manager. If the display-manager restart ever loses its privilege mid-restore,
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`PUNKTFUNK_RECOVER_SESSION_CMD` (see [Configuration](/docs/configuration)) is fired as the
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fallback.
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## Session following
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`PUNKTFUNK_SESSION_WATCH` follows a Gaming ↔ Desktop switch **mid-stream** — the host rebuilds the
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@@ -58,7 +86,7 @@ a model. See the full [Configuration reference](/docs/configuration) for every o
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| Setting | Values | Meaning |
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|---|---|---|
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| `PUNKTFUNK_GAMESCOPE_ATTACH` | `1` | **Attach** model: the box owns its gamescope session (on its own display); the host captures whatever's live and never tears it down. A box-owned autologin session is restarted at the client's resolution on a mismatch; a foreign/bare gamescope streams at its own mode. |
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| `PUNKTFUNK_GAMESCOPE_ATTACH` | `1` | **Attach** model: the box owns its gamescope session (on its own display); the host captures whatever's live and never tears it down. On a **headless** box the box-owned autologin session is restarted at the client's resolution on a mismatch; a box driving a physical display, and any foreign/bare gamescope, streams at its own mode. |
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| `PUNKTFUNK_GAMESCOPE_MANAGED` | `1` | **Managed** model (the default where session infra is detected): the host takes the box's gamescope over and relaunches it headless at the client's exact mode, restoring on idle. |
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| `PUNKTFUNK_GAMESCOPE_SESSION` | `steam` | The host owns a `gamescope-session-plus` (Steam) session at the client's mode — a headless appliance with no physical session running. |
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| `PUNKTFUNK_GAMESCOPE_NODE` | `auto` · node id | Discover and capture a **running** gamescope's PipeWire node at a fixed mode. Do **not** combine with `SESSION`. |
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@@ -107,6 +107,21 @@ See [GNOME](/docs/gnome) for the GL/EGL userspace details.
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auto-detects the live compositor, and the pin points it at one backend even when a different
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session is live (it also disables Gaming ↔ Desktop following).
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## The screen stays black after switching to Game Mode (Nobara)
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On distros whose Game Mode is display-manager autologin under **plasmalogin** (Nobara), a managed
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takeover from a host **0.19.1 or older** could kill the display manager: it trips systemd's start
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limit and the box stays black until someone restarts it. Recover from a VT (Ctrl+Alt+F3) or SSH:
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```sh
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systemctl --user unmask --runtime 'gamescope-session-plus@*.service'
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sudo systemctl reset-failed plasmalogin && sudo systemctl restart plasmalogin
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```
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Current hosts detect the display-manager flavor and never mask the session unit there — see
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[gamescope → autologin display managers](/docs/gamescope) for the polkit rule that enables the full
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managed takeover on these boxes (without it the host mirrors Game Mode instead).
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## Session fails right after editing host.env
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- Keys are **case-sensitive**: `punktfunk_gamescope_attach=1` sets nothing — use the exact
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