Chapter 1: Introduction

Rust is a robust systems programming language that integrates semantic constraints and automated compiler functionalities to foster a secure coding environment. Following the official inclusion of Rust support in the Linux 6.1 kernel, its integration within the Linux ecosystem is now undeniable, paving the way for innovative advancements.

This technological shift presents several implications for both developers and project managers. For developers, crafting a simple “Hello, World” program marks the beginning of their Rust journey. However, project managers face more intricate decisions: should they initiate a project using Rust, and if so, when is the ideal time?

A significant question arises: what makes Rust a viable choice for project development? While security is a paramount consideration, does Rust truly enhance security? Many contemporary programming languages tend to simplify, yet Rust introduces a variety of complex elements—could this steepen the learning curve and obstruct project progression? Such inquiries persist, leaving decision-makers in a challenging position between potential risks and competitive advantages.

This document aims to provide a foundation for addressing these questions through comprehensive, real-world project experiences. To clarify the issues at hand, we will begin with a fresh project, with plans to explore the migration of existing projects in future discussions.

Chapter 2: Practical Implementation

The ongoing integration of Rust with Linux continues to evolve, and newcomers are encouraged to follow a gradual approach: starting with application-level development, then moving to kernel modules, and finally engaging with the kernel itself.

Our initiative focuses on optimizing the performance of the FUSE filesystem, specifically utilizing eBPF dynamic programming (referred to as the BPFuse project). The objective is to enhance the efficiency of file access operations while ensuring the stability, correctness, and compatibility of the filesystem.

We also aim to maintain consistent functionality and performance across various kernel versions. Given the rapid evolution of eBPF from its instruction set to its infrastructure, addressing eBPF instruction compatibility is crucial. Our goal is to achieve long-term, sustainable technical advancements that bolster the capabilities and efficiency of vertical virtual filesystem development. This involves synchronizing eBPF development with business logic enhancement and leveraging the homomorphic properties of data and instructions to foster a unified development model.

The project's foundational technical structure involves extending FUSE with eBPF dynamic capabilities at the kernel level. Concurrently, we are developing a file domain Unilang front-end interpreter (referred to as the interpreter project), which integrates business logic development with eBPF programming. The Unilang-derived language serves as the front-end interface for eBPF, while a Rust-implemented Unilang interpreter generates eBPF programs. Finally, an executor loads these eBPF programs into the kernel, facilitating interaction between the two components.

Given the kernel-centric nature of this project, we have chosen Rust for the interpreter to maximize security. This decision has proven advantageous, alleviating numerous potential issues and instilling confidence in our undertaking.

Chapter 3: Iterative Development

In our interpreter project, we designed a Unilang lexical and syntax parser as the front-end and a semantic module as the back-end, implementing VFS semantics with potential for future expansion. To expedite development, we aimed to avoid unnecessary complexity while ensuring scalability. The overall architecture is straightforward—a tree-like module structure that integrates three core layers while allowing for future module expansion.

We emphasize logical relationships between modules, enabling flexible adjustments in response to changes in module organization. Our objective is to maintain clear, explicit, and minimal coupling among modules while allowing easy access and reference.

Rust’s modular development framework supports this approach. By employing a directory structure and descriptive files, Rust creates an intuitive tree of modules referenced through keywords and paths. This system simplifies project structure definition and minimizes the need for extensive code refactoring, promoting rapid iterative development.

Our project adopts an agile iterative methodology, resulting in multiple code refactorings and module separations. Initially, we implemented a Unilang parser, generating a symbol stream, which served as a basic conversion program. Once the parsing functionality stabilized, we performed our first module split, organizing the software into top shell and front-end/back-end components.

Subsequently, we concentrated on back-end module development to produce eBPF commands, primarily referencing the V5 instruction set and encapsulating generation rules to connect the front and back ends, ultimately yielding our first Unilang-written eBPF program.

Further refactorings allowed us to refine the back-end module, expanding support for VFS semantics and accommodating both V4 and V5 eBPF instruction sets. Additionally, we restructured the upper shell, introducing a Foreign Function Interface (FFI) layer to facilitate C-style dynamic library calls from C/C++ programs.

Throughout this process, the continual addition of features, module splitting, and code refactoring occurred smoothly, thanks to Rust's effective modularization. The language's design includes two organizational levels—Crates and Modules—alongside external organization through Packages and Workspaces, which supports projects of various scales.

The modular architecture is complemented by file management, path management, and namespace management mechanisms. Rust's file management aligns with user habits, while path management utilizes node description files to establish a hierarchical structure. Namespace management employs keywords like "use" and "pub" to facilitate namespace merging and element elimination, enhancing expressiveness and control.

Rust’s namespace management capabilities allow fine-grained control over structural elements, simplifying the library implementation process and enabling developers to tailor module designs to their preferences. This flexibility reduces constraints, making it easier for developers to engage with the language and promote creativity.

Chapter 4: Lightweight Abstraction

Object-oriented programming has long been a favored modeling approach, evident in the Linux kernel’s code, which employs OOP methodologies for readability and maintainability. However, over decades, OOP has evolved into a heavy paradigm, with excessive abstraction layers that complicate design and hinder rapid, iterative development.

In contrast, Rust employs traits—collections of “features”—as its primary abstraction mechanism, offering a lightweight alternative. Traits provide a bridge between procedural and object-oriented paradigms, allowing data types to be manipulated using defined methods.

Rust deliberately avoids the concepts of classes and objects common in OOP, which often introduce significant overhead. This distinction in design philosophy sets Rust apart, presenting advantages over traditional object-oriented system languages.

While Rust is not object-oriented, it delivers a comparable level of abstraction through feature-oriented programming. This approach eliminates the runtime inefficiencies associated with OOP, facilitating a more agile design and execution process. Moreover, Rust's emphasis on compile-time problem resolution strengthens the language's expressiveness and overall efficiency.

Our project’s technical configuration is straightforward, requiring only essential abstraction at key levels to clarify relationships among large modules. By utilizing Rust's abstraction tools, we established three traits—Analyser, InstComposite, and Execute—each representing key aspects of language analysis, code generation, and execution, effectively simplifying programming complexities.

Chapter 5: Ecosystem Integration

Rust's global development model centers around the crates.io URI resource, mapping numerous crates developed by contributors into a unified namespace. This structure fosters collaborative development, ensuring that no Rust project exists in isolation.

A Rust project initiates by exploring crates.io for relevant projects to integrate and extend. As the project evolves, it can incorporate additional resources from crates.io to enhance functionality. This interconnected model streamlines project maintenance by simplifying update synchronization across related initiatives.

In addition to Rust’s ecosystem, its design allows for seamless integration with C libraries, which is crucial for creating a diverse, evolving development landscape. Rust's metaprogramming capabilities facilitate the packaging and inheritance of C libraries, addressing the need for robust functionality in emerging projects.

While Rust's native libraries are still maturing, developers often rely on existing C-style libraries for essential functionalities. However, accessing these libraries requires understanding the data structures defined in C header files. Since Rust cannot directly reference C headers, developers face the challenge of accurately manipulating data structures.

To navigate this, metaprogramming serves as an effective solution. Given the lexical similarities between C and Rust, it is feasible to create a simplified C compiler through metaprogramming. While this task can be intricate, simpler implementations can be achieved with minimal adjustments, facilitating accurate data structure comprehension without compromising the independent development of both languages.

Numerous non-native libraries encapsulating C libraries are available on crates.io, enriching Rust's ecosystem. In cases where a C library lacks packaging, Rust's robust packaging capabilities enable swift implementation, showcasing the language’s strengths.

Ultimately, our project extends beyond merely serving as an interpreter for Unilang; it also functions as an executor, loading the generated eBPF programs into the Linux kernel. This necessitates invoking the Linux system call bpf(), yet Rust currently lacks a wrapper for this functionality.

Consequently, we must encapsulate the relevant data structures and definitions to facilitate the bpf system call, which is clearly outlined in the C header file. Our approach leverages Rust’s encapsulation capabilities, using macros to bridge this gap.

Chapter 6: Conclusion

For managers contemplating the adoption of Rust for project development, it is essential to recognize that Rust is a safe language. Unlike C, where a developer's expertise significantly influences project quality, Rust’s structure ensures that a developer's proficiency does not compromise software integrity.

Furthermore, Rust's design, tools, and development methodologies incorporate modern principles, providing comprehensive support for model design, module organization, iterative updates, and global collaboration across varying project scales. As Rust continues to evolve, it becomes an increasingly powerful and sophisticated tool for developers.

Rust’s safety features revolutionize the development process, leading to reduced debugging, testing, and maintenance overhead, while simultaneously enhancing software quality. Contrary to common misconceptions, Rust is particularly well-suited for rapid iterative development, as its security features streamline the process, making it more efficient and ultimately shortening development timelines.