Required reading: Plan 9 from Bell Labs
- -Had moved away from the ``one computing system'' model of -Multics and Unix.
- -Many computers (`workstations'), self-maintained, not a coherent whole.
- -Pike and Thompson had been batting around ideas about a system glued together -by a single protocol as early as 1984. -Various small experiments involving individual pieces (file server, OS, computer) -tried throughout 1980s.
- -Ordered the hardware for the ``real thing'' in beginning of 1989, -built up WORM file server, kernel, throughout that year.
- -Some time in early fall 1989, Pike and Thompson were -trying to figure out a way to fit the window system in. -On way home from dinner, both independently realized that -needed to be able to mount a user-space file descriptor, -not just a network address.
- -Around Thanksgiving 1989, spent a few days rethinking the whole -thing, added bind, new mount, flush, and spent a weekend -making everything work again. The protocol at that point was -essentially identical to the 9P in the paper.
- -In May 1990, tried to use system as self-hosting. -File server kept breaking, had to keep rewriting window system. -Dozen or so users by then, mostly using terminal windows to -connect to Unix.
- -Paper written and submitted to UKUUG in July 1990.
- -Because it was an entirely new system, could take the -time to fix problems as they arose, in the right place.
- - -Three design principles:
- -
-1. Everything is a file.
-2. There is a standard protocol for accessing files.
-3. Private, malleable name spaces (bind, mount).
-
Everything is a file (more everything than Unix: networks, graphics).
- --% ls -l /net -% lp /dev/screen -% cat /mnt/wsys/1/text -- -
9P is the only protocol the kernel knows: other protocols -(NFS, disk file systems, etc.) are provided by user-level translators.
- -Only one protocol, so easy to write filters and other -converters. Iostats puts itself between the kernel -and a command.
- --% iostats -xvdfdf /bin/ls -- -
Each process has its own private name space that it -can customize at will. -(Full disclosure: can arrange groups of -processes to run in a shared name space. Otherwise how do -you implement mount and bind?)
- -Iostats remounts the root of the name space -with its own filter service.
- -The window system mounts a file system that it serves -on /mnt/wsys.
- -The network is actually a kernel device (no 9P involved) -but it still serves a file interface that other programs -use to access the network. -Easy to move out to user space (or replace) if necessary: -import network from another machine.
- -Everything is a file + can share files => can share everything.
- -Per-process name spaces help move toward ``each process has its own -private machine.''
- -One protocol: easy to build custom filters to add functionality -(e.g., reestablishing broken network connections). - -
Unix sockets are file descriptors, but you can't use the -usual file operations on them. Also far too much detail that -the user doesn't care about.
- -In Plan 9: -
dial("tcp!plan9.bell-labs.com!http");
-
-(Protocol-independent!)
-
-Dial more or less does:
-write to /net/cs: tcp!plan9.bell-labs.com!http
-read back: /net/tcp/clone 204.178.31.2!80
-write to /net/tcp/clone: connect 204.178.31.2!80
-read connection number: 4
-open /net/tcp/4/data
-
Details don't really matter. Two important points: -protocol-independent, and ordinary file operations -(open, read, write).
- -Networks can be shared just like any other files.
- -Similar story for graphics, other resources.
- -Per-process name spaces mean that even full path names are ambiguous -(/bin/cat means different things on different machines, -or even for different users).
- -Convention binds everything together. -On a 386, bind /386/bin /bin. - -
In Plan 9, always know where the resource should be -(e.g., /net, /dev, /proc, etc.), -but not which one is there.
- -Can break conventions: on a 386, bind /alpha/bin /bin, just won't -have usable binaries in /bin anymore.
- -Object-oriented in the sense of having objects (files) that all -present the same interface and can be substituted for one another -to arrange the system in different ways.
- -Very little ``type-checking'': bind /net /proc; ps. -Great benefit (generality) but must be careful (no safety nets).
- - -Plan 9 still is the most portable operating system. -Not much machine-dependent code, no fancy features -tied to one machine's MMU, multiprocessor from the start (1989).
- -Many other systems are still struggling with converting to SMPs.
- -Has run on MIPS, Motorola 68000, Nextstation, Sparc, x86, PowerPC, Alpha, others.
- -All the world is not an x86.
- -New programming language: convenient, but difficult to maintain. -Retired when author (Winterbottom) stopped working on Plan 9.
- -Good ideas transferred to C library plus conventions.
- -All the world is not C.
- -Thompson invented UTF-8. Pike and Thompson -converted Plan 9 to use it over the first weekend of September 1992, -in time for X/Open to choose it as the Unicode standard byte format -at a meeting the next week.
- -UTF-8 is now the standard character encoding for Unicode on -all systems and interoperating between systems.
- -Whole system source code is available, simple, easy to -understand and change. -There's a reason it only took a couple days to convert to UTF-8.
- -- 49343 file server kernel - - 181611 main kernel - 78521 ipaq port (small kernel) - 20027 TCP/IP stack - 15365 ipaq-specific code - 43129 portable code - -1326778 total lines of source code -- -
Snapshot idea might well have been ``in the air'' at the time. -(OldFiles in AFS appears to be independently derived, -use of WORM media was common research topic.)
- -Picked up by other systems: FreeBSD, Linux.
- -No global super-user. -Newer, more Plan 9-like authentication described in later paper.
- -Much faster than gcc, simpler.
- -8s to build acme for Linux using gcc; 1s to build acme for Plan 9 using 8c (but running on Linux)
- -Now retired. -For better or worse, TCP has all the installed base. -IL didn't work very well on asymmetric or high-latency links -(e.g., cable modems).
- -Many ideas have propagated out to varying degrees.
- -Linux even has bind and user-level file servers now (FUSE), -but still not per-process name spaces.
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