Add os9 reveal to identify what lives at a given disk location

[tlindner]

Summary

Add a new os9 reveal command that explains what resides at a given location within an OS-9 RBF disk image.

Given an LSN (optionally with a byte offset) or an absolute byte offset, reveal walks the filesystem metadata and reports, in plain English, what occupies that location.

Features

• Adds the new os9 reveal command.
• Supports:
  • LSN[:offset] addressing.
  • Absolute byte offsets (-b).
  • Dragon boot track layout (-d).
• Identifies locations within:
  • LSN0 fields.
  • Allocation bitmap.
  • File descriptors.
  • Segment tables.
  • Directory entries.
  • File data.
• Recursively traverses the live directory tree to map sectors back to files.
• Reports whether unmapped sectors are:
  • Free.
  • Part of the boot track.
  • Likely remnants of deleted files or other allocated data.
• Detects and reports several forms of filesystem corruption, including:
  • Invalid sector references.
  • Truncated disk images.
  • Corrupt directory structures.
  • Invalid filesystem geometry.

Documentation

• Adds REVEAL to the ToolShed manual.
• Documents syntax, options, behavior, and an example invocation.

Motivation

When debugging OS-9 disk images, it's often difficult to determine what a particular sector or byte actually represents. reveal turns a raw disk location into a human-readable explanation, making filesystem debugging, reverse engineering, and image validation significantly easier.

[DrPitre]

This is very useful.