OSF/1 Internals Student Workbook

This document serves as a student workbook for a four-day technical course on the internal workings of the OSF/1 operating system, designed for system programmers and administrators. It provides a deep dive into the OSF/1 kernel, assuming prior familiarity with UNIX, virtual memory, and common file systems (UFS, NFS, System V).

Key areas covered include:

• OSF/1 Fundamentals: An overview of OSF/1 as a parallelized 4.4BSD UNIX, its Mach kernel, streams implementation, extensible loader, dynamic configurability, and B1-compliance. It details how Mach and UNIX coexist within the OSF/1 kernel and Mach's core abstractions: tasks, threads, messages, ports, and memory objects.
• Process Abstraction: Explores how OSF/1 extends traditional UNIX processes to a multithreaded model, including details on UNIX and Mach system calls, synchronization primitives, thread management, signals, exception handling, scheduling policies (time-shared, fixed-priority, processor sets), thread pools, and zoned memory allocation.
• Messages and Ports: Discusses the structure and flow of messages and ports as communication and object reference mechanisms within the Mach kernel.
• Virtual Memory: Covers lazy evaluation, VM components, memory objects (including the vnode pager and external managers), virtual copy operations, and the pmap module's role in hardware-dependent memory management and TLB shootdown.
• File Systems: Details the representation of open files, virtual file systems (VFS), the buffer cache (including consistency and parallelization), directory path searching (with complexities like mount points and symbolic links), and the specifics of S5, UFS, and NFS file systems, their parallelization, and handling of server crashes and data consistency.
• Device Drivers and Terminal I/O: Explains special files, dynamic configuration of drivers and modules, major driver entry points (open, close, read/write, ioctl, interrupt), terminal I/O concepts (line disciplines, POSIX session management), and pseudo terminals.
• Streams: Introduces streams components (modules, stream head, drivers, multiplexers), message flow, implementation data structures, and parallelization techniques within OSF/1.
• Sockets: Describes socket types (datagram, stream), mbuf data structures for message representation and memory management, and the implementation and parallelization of TCP/IP networking protocols within the socket framework, alongside the XTISO interface for streams compatibility.
• Logical Volume Manager (LVM): Highlights the LVM's role in physical volume spanning, mirroring, logical volume resizing, bad-sector remapping, and its data structures and flow of control for request serialization and crash recovery.
• Loader: Explains the OSF/1 loader's functions, its interaction with exec, shared libraries, symbol resolution, the run-time image, and dynamic loading into both user processes and the kernel.
• Security: Addresses OSF/1's compliance with the "Orange Book" security model, auditing mechanisms, discretionary (DAC) and mandatory (MAC) access control, and the implementation of authorizations and privileges, emphasizing the principle of least privilege.