CB-C6s-STU-GSI-Fixes/AGENTS.md

AGENTS.md — CB-C6s-STU-GSI-Fixes

Overview

TWRP flashable zip for the CB-C6s-STU tablet (Spreadtrum/Unisoc) running a GSI. It appends build.prop properties, installs a touchscreen IDC config, and installs a camera sensor config. All install logic lives in a shell-script update-binary — no compiled code, no build system.

Build / Package

# Create the flashable zip (excluded from git via .gitignore)
cd /home/purpl/Repos/CB-C6s-STU-GSI-Fixes
zip -r ../CB-C6s-STU-GSI-Fixes.zip META-INF/ system/ vendor/

No build dependencies, no lint, no test suite.

Architecture

zip root
├── META-INF/com/google/android/
│   ├── update-binary        ← Entry point: POSIX sh script, executed by TWRP
│   └── updater-script       ← Dummy placeholder (TWRP ignores it)
├── system/
│   ├── build.prop           ← Properties APPENDED (>>) to /system/build.prop
│   └── usr/idc/
│       └── goodix_ts.idc    ← Copied to /system/usr/idc/goodix_ts.idc (644)
└── vendor/etc/
    └── sensor_config.xml    ← Copied to /vendor/etc/ or /system/vendor/etc/ (644)

Install flow (update-binary)

1. Locate zip root: dirname $0 → up 3 levels (../../..)
2. Mount /system and /vendor
3. Append system/build.prop → /system/build.prop (backup first to .bak)
4. Copy goodix_ts.idc → /system/usr/idc/
5. Copy sensor_config.xml → /vendor/etc/ (fallback to /system/vendor/etc/ for SAR)
6. Report success via ui_print() to /proc/self/fd/$OUTFD

Critical constraint: build.prop is APPENDED, never replaced

update-binary line ~72: cat "$BUILDPROP_SRC" >> /system/build.prop

The >> is intentional. Using > or package_extract_dir would clobber the device's existing properties. Re-flashing duplicates entries — warn the user or add idempotency if this becomes a problem.

Key Files

File	Role
META-INF/…/update-binary	Entire install logic (shell script)
META-INF/…/updater-script	Placeholder; not executed
system/build.prop	5 properties appended to device's build.prop
system/usr/idc/goodix_ts.idc	Touchscreen input device config (orientation + type)
vendor/etc/sensor_config.xml	Camera module mapping: hi846, gc8034 (rear/front, 4 combos)
README.md	User-facing documentation
.gitignore	Excludes *.zip

Coding Conventions

• Shell: POSIX sh, no bashisms. Shebang #!/sbin/sh (TWRP environment).
• Error handling: abort() helper exits with message. 2>/dev/null on non-critical operations (mount, mkdir, cp backup).
• Naming: UPPER_CASE for globals/file paths, snake_case for helpers.
• Partition logic: /vendor mount is best-effort; falls back to /system/vendor/etc/ when /vendor/etc/ doesn't exist (SAR compatibility).

Git Workflow

• Branch: main (root commit only)
• Commit style: concise summary line, then bullet list of changes
• .gitignore: excludes *.zip (the build artifact) and tooling directories

Tips for AI Agents

• This is not a software project — there is no build system, no package manager, no test runner. Changes are edits to shell script or config files.
• To add a new fix: add the payload file under system/ or vendor/, add a step to update-binary with ui_print and cp (or append logic), update README.md "What it fixes" table.
• To add a new build.prop property: append a line to system/build.prop. If it needs to be idempotent, add a grep guard in update-binary.
• Testing: flash the zip in TWRP on the device. There is no emulation.
• The updater-script is a dummy — do not add Edify commands there; put all logic in update-binary.
• Zip path: the build artifact is written to the repo's parent directory, not inside the workspace. *.zip in .gitignore covers both locations.