CFS Lock Manager Design and Implementation

This document provides a technical overview of the CFSSRV lock manager, a key component of the Cluster File System (CFS) in the TOPS-20 operating system. It covers:

• Locking Mechanisms: Detailed explanations of file-level locks (open type, write access, ENQ/DEQ) and file section-level access tokens (place-holder, read-only, exclusive).
• Resource Management: How CFS manages distributed resource ownership, token state transitions, and the use of the DDMP routine to flush or update modified pages during state changes.
• Voting Protocols: The distributed, master-less voting mechanism used to acquire or upgrade resources across nodes, including handling of 'conditional yes' responses and fairness timers.
• Concurrency Control: How CFS has integrated with or replaced existing TOPS-20 concurrency control, including the conversion of directory locks and allocation tables into CFS resources.
• Message Summaries: A reference of CFS communication messages, including request, reply, and status update types.