OSF/1 Internals Volume I

This document is a comprehensive course manual titled "OSF/1 Internals Volume I," providing a deep technical introduction to the OSF/1 operating system kernel. OSF/1 integrates enhanced 4.4BSD UNIX functionality with the Mach microkernel, designed from the ground up for parallel and distributed environments.

Key aspects of OSF/1 include:

• UNIX Core: Based on 4.3renoBSD, it supports major file systems (S5, UFS, NFS – with UFS and NFS parallelized) and incorporates SVR3-compatible, transparently parallelized streams for I/O.

• Mach Foundation: The Mach kernel replaces UNIX's virtual memory system and provides fundamental abstractions:

  • Tasks: The basic unit of protection, holding capabilities like address space and communication channels (ports).
  • Threads: The basic unit of scheduling, enabling multithreaded processes within tasks.
  • Messages & Ports: The primary mechanism for inter-thread communication and object referencing.
  • Memory Objects: Abstractions for virtual memory content, which can be files, temporary storage, or user-provided.

• Parallelism & Extensibility: OSF/1 is optimized for shared-memory multiprocessors, allowing most user and kernel processing to execute in parallel. It features an extensible loader for dynamic kernel module loading (e.g., device drivers, file systems, protocols) and supports B1/C2-compliant security. A logical volume manager (from IBM's AIX) enhances file system flexibility and reliability.

• Lazy Evaluation: A pervasive optimization technique used throughout the virtual memory system to postpone operations until necessary, such as page allocation or copying.

The course is structured into modules covering:

• Module 1: Introduction: Defines OSF/1, its kernel organization, threads, parallelism, and Mach's fundamental concepts including its extensible kernel capabilities like network shared memory.
• Module 2: The Process Abstraction: Explores UNIX processes within OSF/1, detailing system calls (UNIX and Mach), kernel synchronization primitives (locks, sleep/wakeup), signal and exception handling, thread management (creation, suspension, termination), scheduling policies (processor sets, thread pools), and zoned memory allocation.
• Module 3: Messages and Ports: Focuses on the structure and handling of messages and ports, including their representation, naming, destruction, and the flow of control during message sending and receiving.
• Module 4: Virtual Memory: Discusses lazy evaluation, the components of the VM system (maps, objects, pages), the vnode pager and external memory object managers, page replacement, swapping, and virtual copy operations utilizing shadow objects. It also covers the architecture-dependent Pmap module and TLB shootdown for cache consistency on multiprocessors.