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172 lines
4.5 KiB
Markdown
172 lines
4.5 KiB
Markdown
# SparkOS Architecture
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## Overview
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SparkOS is designed as a minimal Linux distribution with a custom init system and a modular architecture that allows for future expansion.
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## System Components
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### 1. Init System (`/sbin/init`)
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The init system is the first process started by the kernel (PID 1). It is responsible for:
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- **Mounting filesystems**: proc, sys, dev, tmp
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- **Process management**: Spawning and respawning the shell
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- **Signal handling**: Reaping zombie processes
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- **System initialization**: Setting up the initial environment
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**Implementation**: `src/init.c`
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- Written in C for minimal overhead
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- Statically linked for independence
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- ~100 lines of clean, well-documented code
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### 2. Root Filesystem
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Follows the Filesystem Hierarchy Standard (FHS):
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```
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/
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├── bin/ Essential user binaries (busybox with symlinks)
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├── sbin/ System binaries (init, mount, etc.)
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├── etc/ System configuration files
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├── proc/ Kernel process information (virtual)
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├── sys/ Kernel system information (virtual)
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├── dev/ Device files (virtual)
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├── tmp/ Temporary files
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├── usr/
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│ ├── bin/ Non-essential user binaries
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│ ├── sbin/ Non-essential system binaries
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│ ├── lib/ Libraries for /usr/bin and /usr/sbin
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│ └── lib64/ 64-bit libraries
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├── var/ Variable data (logs, caches)
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├── root/ Root user home directory
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└── home/ User home directories
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```
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### 3. Build System
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**Makefile**: Main build orchestration
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- `make init`: Compile init system
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- `make install`: Install init to rootfs
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- `make image`: Create bootable image (requires root)
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- `make clean`: Clean build artifacts
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**Scripts**:
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- `scripts/build.sh`: Quick build for development
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- `scripts/setup_rootfs.sh`: Create rootfs structure
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- `scripts/create_image.sh`: Create dd-able disk image
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### 4. Boot Process
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```
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Hardware Power-On
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↓
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BIOS/UEFI
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↓
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Bootloader (syslinux)
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↓
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Linux Kernel (vmlinuz)
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↓
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Init System (/sbin/init) [PID 1]
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↓
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Mount filesystems
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↓
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Spawn busybox sh shell
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↓
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User interaction
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```
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## Design Decisions
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### Why Custom Init?
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- **Simplicity**: No dependencies, easy to understand
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- **Control**: Full control over boot process
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- **Size**: Minimal footprint (<1MB statically linked)
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- **Learning**: Educational value for OS development
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### Why Static Linking?
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- **Independence**: No library dependencies
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- **Portability**: Works on any Linux system
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- **Reliability**: No missing library issues
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### Why Busybox?
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- **Minimal**: Single binary provides dozens of utilities
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- **Small footprint**: Typically <1MB for full feature set
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- **Efficient**: Less memory and storage overhead than full GNU coreutils
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- **Standard**: De facto standard for embedded Linux systems
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## Future Architecture
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### Planned Components
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1. **Qt6/QML GUI**
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- Full-screen Wayland application
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- Android-like interface design
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- Desktop-oriented workflow
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2. **Wayland Compositor**
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- Custom compositor for SparkOS
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- Minimal resource usage
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- Touch and mouse support
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3. **C++ CLI Tools**
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- System management utilities
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- Package management
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- Network configuration
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4. **Sudo Integration**
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- Proper privilege elevation
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- Security policies
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- Audit logging
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## Security Considerations
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- Static binaries reduce attack surface
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- Minimal running processes
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- Root filesystem can be read-only
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- Future: sudo for privilege escalation
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- Future: SELinux/AppArmor integration
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## Performance
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- Fast boot time (seconds, not minutes)
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- Low memory footprint (~50MB base system with busybox)
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- No unnecessary background services
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- Efficient init system
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## Portability
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- AMD64 architecture (x86_64)
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- dd-able disk images
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- USB flash drive ready
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- Future: ARM64 support
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## Extension Points
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The architecture is designed for easy extension:
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1. **Init system**: Can be enhanced with service management
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2. **Filesystem**: Can add more mount points and partitions
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3. **Boot process**: Can integrate other bootloaders
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4. **GUI**: Clean separation allows GUI to be optional
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## Development Workflow
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1. Modify source code in `src/`
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2. Build with `make init`
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3. Test init in isolation
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4. Install to `rootfs/` with `make install`
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5. Create test image with `sudo make image`
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6. Test on real hardware or VM
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## References
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- Linux Kernel Documentation
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- Filesystem Hierarchy Standard (FHS)
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- POSIX Standards
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- Qt6 Documentation
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- Wayland Protocol Specification
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