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Architecture

Overview

threshpad is a GNOME Shell extension that manages ThinkPad battery charge thresholds.

┌─────────────────────────────────────┐
│           GNOME Shell               │
│  ┌──────────────────────────────┐   │
│  │      ThreshpadPanel          │   │
│  │  (PanelMenu.Button)          │   │
│  │                              │   │
│  │  • Live BAT0/BAT1 charge %   │   │
│  │  • Preset action menu        │   │
│  └──────────┬───────────────────┘   │
└─────────────┼───────────────────────┘
              │
     ┌────────┴────────┐
     │                 │
  Reads             Writes
     │                 │
     ▼                 ▼
 sysfs files       batctl CLI
 (Gio.File)    (Gio.Subprocess)

Read/Write Split

Reads go directly to sysfs via Gio.File.load_contents(). This avoids subprocess overhead for the 30-second polling loop and is safe because sysfs reads are non-privileged.

Writes go through the batctl binary via Gio.Subprocess. This is required because writing to threshold files needs the battery group (granted via udev rules), and batctl is the authoritative interface for this hardware.

Permissions

The udev rule in udev/99-threshpad.rules grants the battery group write access to charge_control_start_threshold and charge_control_end_threshold for all BAT* devices. The installer adds the user to this group, eliminating any sudo requirement at runtime.

Mock Mode

Setting THRESHPAD_MOCK=1 redirects all sysfs reads to test/fixtures/BAT{0,1}/ and makes batctl invocations no-ops (logging to the journal instead). This allows development and testing on machines without ThinkPad battery hardware.