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diff --git a/web/l-plan9.html b/web/l-plan9.html new file mode 100644 index 0000000..a3af3d5 --- /dev/null +++ b/web/l-plan9.html @@ -0,0 +1,249 @@ +<html> +<head> +<title>Plan 9</title> +</head> +<body> + +<h1>Plan 9</h1> + +<p>Required reading: Plan 9 from Bell Labs</p> + +<h2>Background</h2> + +<p>Had moved away from the ``one computing system'' model of +Multics and Unix.</p> + +<p>Many computers (`workstations'), self-maintained, not a coherent whole.</p> + +<p>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.</p> + +<p>Ordered the hardware for the ``real thing'' in beginning of 1989, +built up WORM file server, kernel, throughout that year.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>Paper written and submitted to UKUUG in July 1990.</p> + +<p>Because it was an entirely new system, could take the +time to fix problems as they arose, <i>in the right place</i>.</p> + + +<h2>Design Principles</h2> + +<p>Three design principles:</p> + +<p> +1. Everything is a file.<br> +2. There is a standard protocol for accessing files.<br> +3. Private, malleable name spaces (bind, mount). +</p> + +<h3>Everything is a file.</h3> + +<p>Everything is a file (more everything than Unix: networks, graphics).</p> + +<pre> +% ls -l /net +% lp /dev/screen +% cat /mnt/wsys/1/text +</pre> + +<h3>Standard protocol for accessing files</h3> + +<p>9P is the only protocol the kernel knows: other protocols +(NFS, disk file systems, etc.) are provided by user-level translators.</p> + +<p>Only one protocol, so easy to write filters and other +converters. <i>Iostats</i> puts itself between the kernel +and a command.</p> + +<pre> +% iostats -xvdfdf /bin/ls +</pre> + +<h3>Private, malleable name spaces</h3> + +<p>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 <i>mount</i> and <i>bind</i>?)</p> + +<p><i>Iostats</i> remounts the root of the name space +with its own filter service.</p> + +<p>The window system mounts a file system that it serves +on <tt>/mnt/wsys</tt>.</p> + +<p>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: +<i>import</i> network from another machine.</p> + +<h3>Implications</h3> + +<p>Everything is a file + can share files => can share everything.</p> + +<p>Per-process name spaces help move toward ``each process has its own +private machine.''</p> + +<p>One protocol: easy to build custom filters to add functionality +(e.g., reestablishing broken network connections). + +<h3>File representation for networks, graphics, etc.</h3> + +<p>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.</p> + +<p>In Plan 9: +<pre>dial("tcp!plan9.bell-labs.com!http"); +</pre> +(Protocol-independent!)</p> + +<p>Dial more or less does:<br> +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 +</p> + +<p>Details don't really matter. Two important points: +protocol-independent, and ordinary file operations +(open, read, write).</p> + +<p>Networks can be shared just like any other files.</p> + +<p>Similar story for graphics, other resources.</p> + +<h2>Conventions</h2> + +<p>Per-process name spaces mean that even full path names are ambiguous +(<tt>/bin/cat</tt> means different things on different machines, +or even for different users).</p> + +<p><i>Convention</i> binds everything together. +On a 386, <tt>bind /386/bin /bin</tt>. + +<p>In Plan 9, always know where the resource <i>should</i> be +(e.g., <tt>/net</tt>, <tt>/dev</tt>, <tt>/proc</tt>, etc.), +but not which one is there.</p> + +<p>Can break conventions: on a 386, <tt>bind /alpha/bin /bin</tt>, just won't +have usable binaries in <tt>/bin</tt> anymore.</p> + +<p>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.</p> + +<p>Very little ``type-checking'': <tt>bind /net /proc; ps</tt>. +Great benefit (generality) but must be careful (no safety nets).</p> + + +<h2>Other Contributions</h2> + +<h3>Portability</h3> + +<p>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).</p> + +<p>Many other systems are still struggling with converting to SMPs.</p> + +<p>Has run on MIPS, Motorola 68000, Nextstation, Sparc, x86, PowerPC, Alpha, others.</p> + +<p>All the world is not an x86.</p> + +<h3>Alef</h3> + +<p>New programming language: convenient, but difficult to maintain. +Retired when author (Winterbottom) stopped working on Plan 9.</p> + +<p>Good ideas transferred to C library plus conventions.</p> + +<p>All the world is not C.</p> + +<h3>UTF-8</h3> + +<p>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.</p> + +<p>UTF-8 is now the standard character encoding for Unicode on +all systems and interoperating between systems.</p> + +<h3>Simple, easy to modify base for experiments</h3> + +<p>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.</p> + +<pre> + 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 +</pre> + +<h3>Dump file system</h3> + +<p>Snapshot idea might well have been ``in the air'' at the time. +(<tt>OldFiles</tt> in AFS appears to be independently derived, +use of WORM media was common research topic.)</p> + +<h3>Generalized Fork</h3> + +<p>Picked up by other systems: FreeBSD, Linux.</p> + +<h3>Authentication</h3> + +<p>No global super-user. +Newer, more Plan 9-like authentication described in later paper.</p> + +<h3>New Compilers</h3> + +<p>Much faster than gcc, simpler.</p> + +<p>8s to build acme for Linux using gcc; 1s to build acme for Plan 9 using 8c (but running on Linux)</p> + +<h3>IL Protocol</h3> + +<p>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).</p> + +<h2>Idea propagation</h2> + +<p>Many ideas have propagated out to varying degrees.</p> + +<p>Linux even has bind and user-level file servers now (FUSE), +but still not per-process name spaces.</p> + + +</body> |