Files

Bernardo Magri a47aa3aff5

Check / eval (push) Successful in 3m4s

Details

fix(snapshots): un-break the GUI — polkit agent + launcher, not an override

Re-diagnosis of the "btrfs-assistant 2.2 segfaults on launch" bug, and
the fix is not the planned nixpkgs override:

1. gdb: the crash is btrfs_util_subvolume_iterator_next() —
   libbtrfsutil's UNPRIVILEGED subvolume-iteration path in btrfs-progs
   6.17.1 (upstream-fixed after 6.17.1, kdave/btrfs-progs 886571653).
   Symbol versions were checked and match: not ABI/link drift.
2. VM A/B on real btrfs: as root it works (exit 0); as a user it
   segfaults (139). The pkexec launcher runs it as root — so the GUI
   path was fine all along, except…
3. …the distro shipped NO polkit authentication agent: every pkexec
   prompt in the session failed silently. That is the actual root
   cause of "the GUI doesn't open".

Shipped: hyprpolkitagent (Hyprland's Qt agent — the prompt is
Stylix-themed) via exec-once in hyprland.nix; `nomarchy-menu snapshot`
prefers btrfs-assistant-launcher again, with the nomarchy-snapshots
fzf flow kept as fallback (and for SSH); checks.snapshot-gui guards
the root path + offscreen GUI event loop on a real btrfs volume so a
lock bump can't silently regress it. No btrfs-progs patch: all our
flows are root-side; the unprivileged fix arrives with a lock bump.

Verified: V0 (flake check) + V2 (snapshot-gui check, executed green) +
V1 (HM generation builds; hyprland.conf carries the agent exec-once;
generated menu passes bash -n with the launcher wiring). Remaining V3
queued: first on-hardware themed polkit prompt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

2026-07-04 10:07:40 +01:00

4.2 KiB

Raw Blame History

Memory — durable lessons, learned the hard way

Curated, not append-only: one line per fact, newest at the top of its section; delete entries that stop being true. Details usually live in a docs/ROADMAP.md decision record — pointer given as (§ item). Add a fact here the moment a debugging session teaches you something a future iteration would otherwise rediscover.

Testing & VM recipes

CI (.gitea/workflows/check.yml) is eval-tier only: the act_runner is a docker container (no systemd, no /dev/kvm). Container gotchas are documented in the workflow header (single-user Nix + nixbld users, sandbox=false for Stylix IFD, Nix pinned 2.31.5 vs lazy-trees, no JS actions past node20) — learned over the legacy repo's 57 runs; read them before touching the workflow.
The git server is Gitea (gitea/act_runner via docker-compose), NOT Forgejo — workflows are read from .gitea/workflows/ (or .github/), never .forgejo/workflows/ (a whole push cycle was lost to that).
Reusable headless VM harness: checks.* via runNixOSTest — existing examples to crib from: distro-id (boots + switch-to-configuration dry-activate), hardware-toggles (kernel cmdline/PAM assertions), battery-charge-limit (fake Mains adapter via test_power, real udev uevent, InvocationID change proves the restart).
Themed-desktop screenshots work headlessly: software-GL Hyprland (LIBGL_ALWAYS_SOFTWARE on virtio-gpu) + machine.screenshot() QMP dump — prototyped 2026-06-19, kept as the fallback for theme previews (§ Visual theme picker).
Hyprland/Ghostty need guest GL (virtio-vga-gl, gl=on) in interactive QEMU or the session won't start; black screen ≈ missing GL (docs/TESTING.md § gotchas).
No KVM = slow, not broken; don't read slowness as failure.

Known-broken / watchlist

btrfs-assistant "segfault" was unprivileged-only (re-diagnosed 2026-07-04): libbtrfsutil's unprivileged subvolume iteration crashes on btrfs-progs 6.17.1 (upstream-fixed after); as root it works, and the pkexec launcher runs it as root. The real distro bug was no polkit agent in the session (every pkexec failed silently) — hyprpolkitagent now ships (hyprland.nix exec-once). checks.snapshot-gui guards the root path. Lesson: before "app X is broken", check WHO it runs as — and whether polkit prompts can render at all (§ Snapshot browse/restore).
NixOS release bump is a trap: the discarded attempt (branch deleted 2026-06-22) hit a Hyprland OOM blocker; a redo is a deliberate v2, never part of routine lock bumps.
theme-state.json is git-tracked inside an 86 MB flake tree, so every state write re-copies the source before eval — the wallpapers-artifact split (BACKLOG LATER) is the decided fix (§ Faster switches).

Gotchas (cost a debugging session once)

Never kill a Wayland session-lock client (hyprlock): its crash failsafe drops to a tty instead of unlocking (§ Hibernate double-unlock).
rofi element-icon size is one value = a square cell; WxH silently collapses and non-square icons letterbox — pre-crop images square at build (§ Visual theme picker).
WirePlumber 0.5 monitor rules can only early-match device.api; device.product.name etc. bind after the rule runs — surgical libcamera scoping is impossible (§ Webcam).
hyprctl switchxkblayout is a global layout flip; per-device isolation needs device[<name>]:kb_layout keywords (§ Keyboard layouts).
Waybar's clock captures the timezone at construction — a zone change needs SIGUSR2 (watcher in timezone.nix) (§ Automatic timezone).
Waybar persistent_workspaces (underscore) is dead syntax silently ignored; the hyphen form is honoured and renders phantom workspaces (§ Waybar shows non-existent workspaces).
GTK4/libadwaita/Qt6 read light/dark from the portal's org.freedesktop.appearance color-scheme (dconf), not Stylix polarity (§ GTK/Qt ignore the theme's mode).
Update order matters downstream: sys-update (lock) before home-update, or desktop changes are silently skipped against the old lock (README § 3).
grub loadfonts every .pf2 in a theme dir — reuse a bundled DejaVu rather than shipping fonts (§ Distro branding).

4.2 KiB Raw Blame History

Memory — durable lessons, learned the hard way

Testing & VM recipes

Known-broken / watchlist

Gotchas (cost a debugging session once)

4.2 KiB

Raw Blame History