How can you build a modular operating system?

1 Modular OS concept

A modular OS is based on the idea of dividing the system into smaller and independent units, called modules, that can be loaded and unloaded as needed. Modules can be either user-level or kernel-level, depending on whether they run in the same or separate address space as the kernel. User-level modules are also called servers, and they communicate with the kernel and other servers through message passing or remote procedure calls. Kernel-level modules are also called extensions, and they communicate with the kernel and other extensions through direct function calls or shared data structures. A modular OS can have different types of modules, such as file systems, device drivers, network protocols, security mechanisms, or graphical user interfaces.

2 Benefits of modular OS

One of the main benefits of a modular OS is that it allows for greater flexibility and customization of the system. Users can choose which modules to include or exclude, depending on their needs and preferences. For example, they can select a different file system or network protocol for different devices or applications. Another benefit is that it improves the reliability and security of the system. If a module fails or is compromised, it can be isolated and replaced without affecting the rest of the system. Moreover, modules can be updated and tested independently, reducing the risk of introducing bugs or vulnerabilities. A third benefit is that it enhances the performance and efficiency of the system. Modules can be loaded and unloaded dynamically, saving memory and CPU resources. Furthermore, modules can be optimized and parallelized for specific tasks or hardware platforms.

3 Challenges of modular OS

However, building a modular OS also poses some challenges and trade-offs. One of the main challenges is to design a coherent and consistent interface between the kernel and the modules, as well as between the modules themselves. The interface should be well-defined, stable, and compatible, to ensure that the modules can work together seamlessly and correctly. Another challenge is to balance the trade-off between modularity and performance. While modularity can improve performance by reducing the size and complexity of the kernel, it can also degrade performance by increasing the overhead and latency of communication between modules. Moreover, modularity can introduce new sources of errors or conflicts, such as incompatible or outdated modules, or malicious or faulty modules.

4 Examples of modular OS

Modular operating systems (OSes) are present in the real world, each with its own design and implementation choices. Linux is a monolithic kernel OS with loadable kernel modules (LKMs) that can be inserted or removed at runtime. LKMs provide device drivers, file systems, network protocols, or other functionalities, as well as user-level servers like systemd or X Window System that communicate with the kernel and other servers through sockets or pipes. Windows has a hybrid kernel with kernel-mode drivers (KMDs) that run in the same address space as the kernel and user-mode drivers (UMDs) that run in separate address spaces. KMDs provide low-level hardware access and UMDs provide higher-level functionalities, such as graphics or audio. Windows also supports user-level services such as Windows Services or Windows Subsystem for Linux that communicate with the kernel and other services through interprocess communication (IPC) mechanisms. Minix is a microkernel OS with minimal functionalities such as scheduling, memory management, and interprocess communication. All other functionalities are provided by user-level servers like file systems, device drivers, network protocols, or shells. Minix uses message passing as the main communication method between the kernel and the servers, as well as between the servers themselves.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?