Plan 9 From Bell Labs

Take-away points

• 9P: network protocol
• everything is file
• customize namespace

Reading Notes

• 9P: a network-level protocol, enable machines to access files on remote systems.
  • implement RPCs for all file “methods"
• naming system: let people and their computing agents build customized views of the resources in the network.

Design

• Terminal: home-resident workstations or PCs.
  • Personalized terminal: file-oriented
• 9P protocol: a set of transactions
  • control file system
  • file access is at the level of bytes

Command-level View

• Each window is created in a separate name space.

File Server

• single tree hierarchy
• memory buffer, disk, WORM
• WORM is for backup.
  • Access permissions of files in the dump are the same as they were when the dump was made.
  • Once a file is written to WORM, it cannot be removed.

Unusual File Server

• cpu: connects the local terminal to CPU

Configuration and administration

• central servers - amortize costs and administration
  • files
  • administration and maintenance
  • network information
  • dump file system (how about the file changes? or permission changes?)

Name Spaces

In computing, a namespace is a set of symbols that are used to organize objects of various kinds, so that these objects may be referred to by name.

• file systems are namespaces that assign names to files
• programming languages organize their variables and subroutines in namespaces
• computer networks and distributed systems assign names to resources, such as computers, printers, websites, (remote) files, etc.

• 9P treats files as a sequence of bytes rather than blocks.
• fids: established pointers to objects in the remote file server.
• mount table: The kernel representation of the name space
• Each file in Plan 9 is uniquely identified by a set of integers
  • type of the channel
  • server or device number
  • qid (analogous to the i-number): formed from two 32-bit numbers called path and version (used to maintain cache coherency between clients and servers).

File caching

• The large memory of central file server acts as a shared cache for all its clients.

Networks and Communication Devices

• Call setup and shutdown are achieved by writing text strings to the control file associated with the device.
• Information is sent and received by reading and writing the data file.
• a call is initiated by writing a connect message with a network-specific address as its argument.
• a listener to specific port indicates its willingness to receive calls to this port.

Authenication

The Data Encryption Standard (DES) was once a predominant symmetric-key algorithm for the encryption of electronic data.

• Each user has an associated DES authenication key
• Authetication is bilateral
• authentication server: maintain the database of keys
• no super user
• None: a special user (analogous to the anonymous user in FTP services)

Q: What does it mean, "9P is really the core of the system; it is fair to say that the Plan 9 kernel is primarily a 9P multiplexer"?

In electronics, a multiplexer (or mux) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line.

An electronic multiplexer can be considered as a multiple-input, single-output switch, and a demultiplexer as a single-input, multiple-output switch.

Class Notes

Plan9 Mode

• node specialized for particular task
• cost-effective

Uniform abstraction

• Key Abstractions: Files + file servers + name spaces
• Plan 9 treat everything as a file
  • All objects have same interface: a file
  • All objects implement file operation/methods

Name Space

• Everything is visible in the file system name space

Storage Hierarchy

• WORM
• no backups
• daily snapshots
  • why are daily snapshots feasible
    • only changes -> incremental backup
    • every month -> full backup

Influence to today

• UTF-8
• rfork: BSD, Linux (clone)
• /n/dump: .snapshot in Waffle (NetApp)