Add .github/copilot-instructions.md for AI-assisted development (#25437)

Signed-off-by: Rustiqly <[email protected]>
Co-authored-by: Rustiqly <[email protected]>
Signed-off-by: Feng Pan <[email protected]>

Author: rustiqly

.github/copilot-instructions.md

@@ -0,0 +1,107 @@
+# Copilot Instructions for sonic-buildimage
+
+## Project Overview
+
+sonic-buildimage is the master build system for SONiC (Software for Open Networking in the Cloud). It produces ONIE-compatible network operating system installer images for network switches across multiple ASIC platforms (Broadcom, Mellanox/NVIDIA, Marvell, etc.). This is the central repo that pulls in all other SONiC components as submodules and builds them into a complete NOS image.
+
+## Architecture
+
+```
+sonic-buildimage/
+├── device/           # Platform-specific device configurations and plugins
+├── dockers/          # Dockerfile definitions for all SONiC containers
+├── files/            # Configuration files, scripts, and templates
+├── installer/        # ONIE installer scripts
+├── platform/         # Platform-specific build rules and configurations
+├── rules/            # Makefile rules for building individual components
+├── scripts/          # Build helper scripts
+├── sonic-slave-*/    # Build environment container definitions (per Debian version)
+├── src/              # Source code and submodules for SONiC components
+├── .azure-pipelines/ # CI/CD pipeline definitions
+├── Makefile          # Top-level build entry point
+└── .github/          # GitHub Actions and PR templates
+```
+
+### Key Concepts
+- **Rules system**: Each component has a `.mk` file in `rules/` defining how to build it
+- **Docker containers**: SONiC services run in Docker containers defined in `dockers/`
+- **Platform abstraction**: `device/` and `platform/` directories abstract hardware differences
+- **Build slaves**: Builds run inside Debian-versioned containers (bookworm, bullseye, etc.)
+- **Submodules**: Most SONiC components are git submodules under `src/`
+
+## Language & Style
+
+- **Primary languages**: Makefile, Shell (bash), Python, Jinja2 templates
+- **Makefile style**: Use tabs for indentation in Makefiles (GNU Make requirement)
+- **Shell scripts**: Use `#!/bin/bash`, 4-space indentation
+- **Python**: Follow PEP 8, 4-space indentation
+- **Naming**: Use snake_case for variables and functions in shell/Python; UPPER_CASE for Make variables
+
+## Build Instructions
+
+```bash
+# Clone with submodules
+git clone --recurse-submodules https://github.com/sonic-net/sonic-buildimage.git
+cd sonic-buildimage
+
+# Initialize build environment
+make init
+
+# Configure for a specific platform
+make configure PLATFORM=vs  # Virtual Switch for testing
+# Other platforms: broadcom, mellanox, marvell-teralynx, etc.
+
+# Build the image
+make SONIC_BUILD_JOBS=4 target/sonic-vs.img.gz
+
+# Build specific component
+make target/debs/bookworm/swss_1.0.0_amd64.deb
+```
+
+### Build Environment Requirements
+- Multiple CPU cores, 8+ GiB RAM, 300+ GiB disk
+- Docker installed and running
+- KVM virtualization support (for some builds)
+
+## Testing
+
+- **VS (Virtual Switch)** platform is the primary testing platform
+- CI runs on Azure Pipelines (`.azure-pipelines/`)
+- Test images are built with `PLATFORM=vs`
+- Integration tests run against VS images in sonic-mgmt repo
+- Use `pytest.ini` at the root for Python test configuration
+
+## PR Guidelines
+
+- **Commit format**: `[component/folder]: Description of changes`
+- **Signed-off-by**: All commits MUST include `Signed-off-by: Your Name <email>` (DCO requirement)
+- **CLA**: Sign the Linux Foundation EasyCLA before contributing
+- **Single logical change per PR**: Isolate each commit to one component/bugfix/feature
+- **Submodule updates**: When updating a submodule, reference the PR in the submodule repo
+- **PR description**: Include what changed, why, and how to test
+
+## Common Patterns
+
+- **Adding a new package**: Create a `.mk` file in `rules/`, add source in `src/`
+- **Adding a Docker container**: Create Dockerfile in `dockers/`, add build rule in `rules/`
+- **Platform support**: Add platform config in `device/<vendor>/`, build rules in `platform/`
+- **Version pinning**: Dependencies are version-pinned in rules files
+- **Build flags**: Use `ENABLE_*` and `INCLUDE_*` variables to toggle features
+
+## Dependencies
+
+- All SONiC repos are submodules (sonic-swss, sonic-sairedis, sonic-utilities, etc.)
+- Debian base system (bookworm/bullseye)
+- Docker for containerized builds
+- Azure Pipelines for CI/CD
+
+## Gotchas
+
+- **Build times**: Full builds take 2-6 hours; use `SONIC_BUILD_JOBS` to parallelize
+- **Disk space**: Builds require 100+ GiB; clean with `make clean` or `make reset`
+- **Submodule versions**: Always check that submodule pins are correct before building
+- **Docker cache**: Build uses Docker layer caching; `make clean` to force rebuild
+- **Branch compatibility**: Component branches must match buildimage branch (e.g., master ↔ master)
+- **Make variables**: Many build options are controlled by variables in `rules/config`
+- **Platform differences**: Some features are platform-specific; check `rules/config` for `ENABLE_*` flags
+- **Do NOT modify files in `src/` directly**: Changes should go to the respective submodule repos