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Check for status of tty1 during startup

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Johannes Leupolz 2025-12-23 20:26:07 +00:00
parent 77c3452bbb
commit 04bd88f179
3 changed files with 89 additions and 13 deletions
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20
docs/DESIGN.md
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@ -499,7 +499,7 @@ As a result:
* input devices may interact with the VT layer in unintended ways
When a graphical session is active, these issues do not occur:
the compositor, via `systemd-logind`, owns a VT, switches it to `KD_GRAPHICS`, and the VT keyboard handler is disabled automatically.
the compositor, via `systemd-logind`, owns a VT, switches it to `KD_GRAPHICS`, and the VT keyboard handler is **suppressed**.
The missing piece is a **well-defined fallback** for the “no graphical session” case.
@ -511,12 +511,12 @@ The missing piece is a **well-defined fallback** for the “no graphical session
It runs only when **no other graphical session is active** on the seat and exists solely to:
* open a regular logind session
* open a regular logind session **of class `greeter**`
* occupy the assigned VT
* let logind switch the VT to `KD_GRAPHICS`
* let logind switch the VT to `KD_GRAPHICS` **and mute the keyboard handler**
`fallbackdm` itself does **not** manipulate VTs, perform `KDSETMODE` ioctls, or access `/dev/tty` directly.
All VT and seat handling is delegated to `systemd-logind`.
All VT and seat handling is delegated to `systemd-logind` **via a standard PAM session**.
---
@ -524,15 +524,13 @@ All VT and seat handling is delegated to `systemd-logind`.
* `fallbackdm` starts as a normal session on the seat
* while active:
* the VT is in `KD_GRAPHICS`
* VT keyboard handling and `getty` input are suppressed
* **the kernel VT keyboard handler is muted (equivalent to `K_OFF` or `KDSKBMUTE`)**
* `getty` input is suppressed
* when a real graphical session (greeter or compositor) starts:
* logind deactivates `fallbackdm`
* VT ownership is transferred automatically
* when the graphical session ends:
* `fallbackdm` may be restarted to reclaim the fallback role
`fallbackdm` is non-interactive by design but may display **minimal status information** in the future.
@ -546,7 +544,6 @@ This design:
* reuses existing, well-tested logind behavior
* avoids duplicating VT and seat logic
* guarantees compatibility with:
* Wayland compositors
* graphical login managers
* multi-seat setups
@ -560,13 +557,10 @@ Conceptually, `fallbackdm` acts as a **headless placeholder graphical session**
* **Direct VT management (KDSETMODE, VT ioctls)**
Rejected due to complexity, fragility, and duplication of logind functionality.
* **Filtering input at the evdev / uinput layer**
Rejected as insufficient: it does not address VT keyboard handling or `getty` behavior.
* **Disabling gettys or VT switching globally**
Rejected to preserve emergency local access and standard Linux behavior.
Rejected to preserve emergency local access and standard Linux behavior. **The logind-managed approach allows physical VT switching to remain functional for debugging.**
* **Depending on a full display manager**
Rejected, as this may require dummy display devices in headless configurations and adds unnecessary complexity.