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1 pagesetup
12 B f
(Plan 9, A Distributed System)4 1485 1 2137 1230 t
10 I f
(Dave Presotto)1 574 1 2593 1470 t
(Rob Pike)1 363 1 2698 1590 t
(Ken Thompson)1 603 1 2578 1710 t
(Howard Trickey)1 652 1 2554 1830 t
10 R f
(AT&T Bell Laboratories)2 993 1 2383 2010 t
(Murray Hill, New Jersey 07974)4 1267 1 2246 2130 t
10 I f
(ABSTRACT)2643 2510 w
10 R f
( environment physically distributed across many machines.)6 2439(Plan 9 is a computing)4 911 2 1330 2770 t
( itself is transparent to most programs giving both users and administra-)11 2950(The distribution)1 650 2 1080 2890 t
( properties make)2 679( Two)1 240( environment.)1 562(tors wide latitude in configuring the topology of the)8 2119 4 1080 3010 t
( name space and uniform access to all resources by rep-)10 2251(this possible: a per process group)5 1349 2 1080 3130 t
(resenting them as files.)3 921 1 1080 3250 t
10 B f
(1. Introduction)1 670 1 720 3610 t
10 R f
(Plan 9 is a general-purpose, multi-user, portable distributed system implemented on a variety of com-)14 4070 1 970 3766 t
( commands, libraries, and system calls are similar to those of the Unix oper-)13 3095( Because)1 386(puters and networks.)2 839 3 720 3886 t
( casual user)2 477( A)1 128( it is possible to port many Unix programs to Plan 9 with little or no changes.)16 3182(ating system,)1 533 4 720 4006 t
(would find little difference between the two systems.)7 2119 1 720 4126 t
( goals of this organization were to reduce adminis-)8 2048( The)1 207(What distinguishes Plan 9 is its organization.)6 1815 3 970 4282 t
( believe that a small)4 807( We)1 190( minimalism.)1 531( programming style was)3 972( Our)1 208(tration and to promote resource sharing.)5 1612 6 720 4402 t
( with much less code, provide most of the function of a larger sys-)13 2698(number of well-chosen abstractions can,)4 1622 2 720 4522 t
( its contemporaries)2 778( is the approach that made the Unix operating system so much smaller than)13 3129(tem. This)1 413 3 720 4642 t
( proven ideas from the Unix operating system rather)8 2173( building Plan 9, we generalized)5 1337( In)1 143(such as Multics.)2 667 4 720 4762 t
(than add new untried concepts.)4 1239 1 720 4882 t
( CPU servers concentrate computing power)5 1743( Diskless)1 390(Plan 9 is divided along lines of service function.)8 1937 3 970 5038 t
( give each user of the)5 870(into large multiprocessors; file servers provide repositories for storage; and terminals)10 3450 2 720 5158 t
( sharing)1 320( The)1 205(system a dedicated computer with bitmap screen and mouse on which to run a window system.)15 3795 3 720 5278 t
( of programmers, amor-)3 971(of computing and file storage services provides a sense of community for a group)13 3349 2 720 5398 t
(tizes costs, and centralizes and hence simplifies management and administration.)9 3231 1 720 5518 t
( CPU servers and terminals use the same kernel, users may choose whether to run pro-)15 3634(Since both)1 436 2 970 5674 t
( 9 provides this flexibility without con-)6 1597( Plan)1 233(grams locally on their terminals or remotely on CPU servers.)9 2490 3 720 5794 t
( to be as dis-)4 517( both users and administrators can configure their environment)8 2523( Therefore,)1 469(straining the choice.)2 811 4 720 5914 t
( like workstations run-)3 911( work, users tend to use their terminals more)8 1810( At)1 154(tributed or centralized as they wish.)5 1445 4 720 6034 t
( data or compute intensive jobs such)6 1472(ning all interactive programs locally and reserving the CPU servers for)10 2848 2 720 6154 t
( home, connected via a dedicated 9600 baud line to work,)10 2311( At)1 151( and computing chess end games.)5 1342(as compiling)1 516 4 720 6274 t
( applications, such as)3 852( Some)1 279(users choose what they run locally and remotely to reduce communication cost.)11 3189 3 720 6394 t
(the editor [Pik87], are split into multiple programs to make this choice even more flexible.)14 3613 1 720 6514 t
( CPU)1 225( Multiprocessor)1 660( we have configured our environment.)5 1549(Figure 1 in any Plan 9 paper shows how)8 1636 4 970 6670 t
( rooms and connected via 7 megabyte/sec point-to-point)7 2328(and file servers are clustered in a few computer)8 1992 2 720 6790 t
( servers to be used as high performance compute engines without)10 2776( permits the CPU)3 740( This)1 244(links [Pre88].)1 560 4 720 6910 t
( servers via lower speed, lower cost distribution)7 1936( are connected to the)4 845( Terminals)1 460(becoming starved for data.)3 1079 4 720 7030 t
( emphasizing the)2 697( By)1 177( 10 megabit Ethernet [Met80] and 2 megabit Incon [Kal, Res].)10 2590(networks such as the)3 856 4 720 7150 t
( the same)2 379( At)1 151( quickly and cheaply incorporate new technologies as they arise.)9 2581(shared service clusters we can)4 1209 4 720 7270 t
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10 R f
(- 2 -)2 166 1 2797 480 t
( incorporate as much computing power as they wish in their own)11 2687(time, users wishing more autonomy can)5 1633 2 720 840 t
(offices without losing the advantage of transparently sharing other resources.)9 3077 1 720 960 t
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1915 1402 14 14 De
1872 1402 14 14 De
1828 1402 14 14 De
1785 1402 14 14 De
1749 1402 14 14 De
1951 1402 14 14 De
1994 1402 14 14 De
1994 1446 14 14 De
1951 1446 14 14 De
1915 1446 14 14 De
1872 1446 14 14 De
1828 1446 14 14 De
1785 1446 14 14 De
1749 1446 14 14 De
1749 1489 14 14 De
1785 1489 14 14 De
1828 1489 14 14 De
1872 1489 14 14 De
1915 1489 14 14 De
1951 1489 14 14 De
1994 1489 14 14 De
1807 1158 1807 1338 Dl
1922 1158 1807 1158 Dl
1922 1338 1922 1158 Dl
1807 1338 1922 1338 Dl
1771 1122 1771 1374 Dl
1951 1122 1771 1122 Dl
1951 1374 1951 1122 Dl
1771 1374 1951 1374 Dl
1713 1389 1713 1518 Dl
2044 1388 1713 1388 Dl
2044 1517 2044 1388 Dl
1713 1518 2044 1518 Dl
2217 1417 14 14 De
2181 1438 14 14 De
2145 1417 14 14 De
2145 1388 86 86 De
1713 1446 1713 1446 1670 1446 Ds
1713 1446 1670 1446 1670 1331 Ds
1670 1446 1670 1331 1770 1331 Ds
1670 1331 1770 1331 1770 1331 Ds
2188 1345 2188 1345 2188 1295 Ds
2188 1345 2188 1295 2102 1309 Ds
2188 1295 2102 1309 2045 1281 Ds
2102 1309 2045 1281 1973 1324 Ds
2045 1281 1973 1324 1973 1324 Ds
2448 1690 14 14 De
2404 1690 14 14 De
2361 1690 14 14 De
2318 1690 14 14 De
2282 1690 14 14 De
2484 1690 14 14 De
2527 1690 14 14 De
2527 1734 14 14 De
2484 1734 14 14 De
2448 1734 14 14 De
2404 1734 14 14 De
2361 1734 14 14 De
2318 1734 14 14 De
2282 1734 14 14 De
2282 1777 14 14 De
2318 1777 14 14 De
2361 1777 14 14 De
2404 1777 14 14 De
2448 1777 14 14 De
2484 1777 14 14 De
2527 1777 14 14 De
2340 1446 2340 1626 Dl
2455 1446 2340 1446 Dl
2455 1626 2455 1446 Dl
2340 1626 2455 1626 Dl
2304 1410 2304 1662 Dl
2484 1410 2304 1410 Dl
2484 1662 2484 1410 Dl
2304 1662 2484 1662 Dl
2246 1677 2246 1806 Dl
2577 1676 2246 1676 Dl
2577 1805 2577 1676 Dl
2246 1806 2577 1806 Dl
2750 1705 14 14 De
2714 1726 14 14 De
2678 1705 14 14 De
2678 1676 86 86 De
2246 1734 2246 1734 2203 1734 Ds
2246 1734 2203 1734 2203 1619 Ds
2203 1734 2203 1619 2303 1619 Ds
2203 1619 2303 1619 2303 1619 Ds
2721 1633 2721 1633 2721 1583 Ds
2721 1633 2721 1583 2635 1597 Ds
2721 1583 2635 1597 2578 1569 Ds
2635 1597 2578 1569 2506 1612 Ds
2578 1569 2506 1612 2506 1612 Ds
1749 1978 1461 1777 Dl
1994 1856 1872 1525 Dl
2325 1978 2404 1813 Dl
(distribution)1806 1962 w
1749 1857 1749 2101 Dl
2325 1856 1749 1856 Dl
2325 2100 2325 1856 Dl
1749 2101 2325 2101 Dl
(network)1874 2042 w
2016 2122 2016 2122 2016 2194 Ds
2016 2122 2016 2194 2052 2266 Ds
2016 2194 2052 2266 2088 2266 Ds
2052 2266 2088 2266 2124 2338 Ds
2088 2266 2124 2338 2124 2474 Ds
2124 2338 2124 2474 2124 2474 Ds
3794 2194 3794 2194 3794 2302 Ds
3794 2194 3794 2302 3866 2338 Ds
3794 2302 3866 2338 3866 2474 Ds
3866 2338 3866 2474 3866 2474 Ds
(Nationwide Long Haul)2 921 1 2448 2675 t
10 B f
(Figure 1 - Plan 9 Topology)5 1137 1 2311 4384 t
10 R f
( topology.)1 417(The rest of this paper describes the features of Plan 9 that make possible such a flexible)16 3653 2 970 4660 t
( details of)2 408( For)1 196(For more information on hardware and use of the system, see our previous paper [Pik90] .)15 3716 3 720 4780 t
(the file server, see [Qui] .)5 1016 1 720 4900 t
10 B f
(2. Minimalism)1 642 1 720 5140 t
10 R f
( program memory, reside in one name space and)8 2001(All resources that a process can access, aside from)8 2069 2 970 5296 t
( look like file systems and, hence-)6 1386( stated, all resources are implemented to)6 1635( Simply)1 345(are accessed uniformly.)2 954 4 720 5416 t
( systems can be the)4 799( File)1 213( with no links.)3 594( file system is a strict tree)6 1057( A)1 128(forth, we shall call them file systems.)6 1529 6 720 5536 t
( They)1 263( the shared file servers.)4 954(traditional type representing persistent storage on a disk as implemented by)10 3103 3 720 5656 t
( file)1 167( The)1 213(can also represent physical devices such as terminals or complex abstractions such as processes.)13 3940 3 720 5776 t
(systems can be implemented by kernel resident drivers, by user level processes, or by remote servers.)15 4047 1 720 5896 t
( example, an)2 533( For)1 202( representing a physical device normally contains one or two files.)10 2778(A file system)2 557 4 970 6052 t
( is represented as a directory containing a)7 1675(RS232 line)1 452 2 720 6172 t
10 CW f
(data)2875 6172 w
10 R f
(and a)1 216 1 3143 6172 t
10 CW f
(ctl)3387 6172 w
10 R f
(file. The)1 366 1 3595 6172 t
10 CW f
(data)3989 6172 w
10 R f
(file is the stream of)4 783 1 4257 6172 t
( The)1 209(bytes transmitted/received on the line.)4 1535 2 720 6292 t
10 CW f
(ctl)2493 6292 w
10 R f
(file is a control channel used to change device parameters)9 2338 1 2702 6292 t
(such as baud rate.\262)3 759 1 720 6412 t
( variables \(as in Unix\) are implemented)6 1598( Environment)1 575( software concepts.)2 773(Some file systems represent)3 1124 4 970 6568 t
( with sepa-)2 438( processes themselves are represented as directories)6 2066( Even)1 256(as files in a kernel resident file system.)7 1560 4 720 6688 t
( things)1 276( Many)1 289( and control.)2 514(rate files representing different aspects of the process such as memory, text file,)12 3241 4 720 6808 t
( Plan 9;)2 322(that require a system call in other operating systems are represented by I/O operations on files in)16 3998 2 720 6928 t
8 S1 f
(__________________)720 7028 w
8 R f
(\262 We neither need nor have an)6 971 1 720 7128 t
8 CW f
(ioctl)1711 7128 w
8 R f
(system call.)1 375 1 1971 7128 t
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10 R f
(- 3 -)2 166 1 2797 480 t
(reading the id of a process, the user id associated with a process, the time, etc.)15 3113 1 720 840 t
(A kernel data structure, called a)5 1288 1 970 996 t
10 I f
(channel,)2287 996 w
10 R f
( user level file descriptor is)5 1109( A)1 127( pointer to a file.)4 683(is used as a)3 464 4 2657 996 t
( nine primitive operations)3 1048( I/O system calls eventually translate into)6 1696( All)1 185(just a handle for a kernel channel.)6 1391 4 720 1116 t
( are:)1 174( They)1 255(on channels.)1 499 3 720 1236 t
( file system is told which user is attaching.)8 1702( The)1 205( point a channel to the root of a file system.)10 1734(attach \261)1 300 4 720 1392 t
( new channel points to the same file as the old one.)11 2036( The)1 205( make a copy of a channel.)6 1066(clone \261)1 300 4 720 1548 t
( do a one level directory lookup on the channel and point it to the new file \(or directory\).)18 3541(walk \261)1 300 2 720 1704 t
( get the attributes of the file pointed to.)8 1557(stat \261)1 300 2 720 1860 t
( change the attributes of the file pointed to.)8 1717(wstat \261)1 300 2 720 2016 t
( check permissions prior to I/O on the channel.)8 1872(open \261)1 300 2 720 2172 t
( read from the opened file.)5 1058(read \261)1 300 2 720 2328 t
( write to the opened file.)5 976(write \261)1 300 2 720 2484 t
( close the opened file.)4 873(close \261)1 300 2 720 2640 t
(Each kernel resident file system is implemented by a)8 2172 1 970 2796 t
10 I f
(device driver)1 532 1 3176 2796 t
10 R f
(containing a procedure for each)4 1298 1 3742 2796 t
( via a kernel array,)4 784( device drivers are accessed indirectly)5 1569( The)1 216(primitive operation.)1 805 4 720 2916 t
10 CW f
(devtab,)4129 2916 w
10 R f
(which con-)1 456 1 4584 2916 t
( channel contains an offset into)5 1270( Each)1 254(tains 9 pointers per driver, one to each primitive procedure.)9 2406 3 720 3036 t
10 CW f
(devtab)4680 3036 w
10 R f
(indicating the driver to be used in accessing the file it points to.)12 2534 1 720 3156 t
( resident in the kernel is via a special device driver, the)11 2239(Accessing file systems not)3 1072 2 970 3312 t
10 I f
(mount driver.)1 548 1 4310 3312 t
10 R f
(All)4912 3312 w
( mount driver turns)3 814( The)1 220( this driver contain a pointer to a communication channel.)9 2443(channels pointing to)2 843 4 720 3432 t
( mount)1 301( The)1 225( channel.)1 380(operations on such channels into request messages written to the communication)10 3414 4 720 3552 t
( the messages on the)4 865( Because)1 393( a multiplexor allowing multiple outstanding messages.)6 2280(driver is written as)3 782 4 720 3672 t
(communication channel are transmitted using)4 1832 1 720 3792 t
10 CW f
(read's)2580 3792 w
10 R f
(and)2968 3792 w
10 CW f
(write's,)3140 3792 w
10 R f
(any type of channel can be used: a)7 1392 1 3648 3792 t
( The)1 209(pipe to a process, a network connection, even an RS232 line.)10 2472 2 720 3912 t
10 CW f
(mount)3430 3912 w
10 R f
(system call, described below, is)4 1281 1 3759 3912 t
(used to create a new mount device channel and supply a communication channel for it.)14 3468 1 720 4032 t
( encapsulate)1 498( code used to)3 545( The)1 212(All Plan 9 components are connected using this file system protocol.)10 2815 4 970 4188 t
( Com-)1 279( mount driver is 899 lines long.)6 1259( The)1 206( long.)1 229(the primitives into request and reply messages is 580 lines)9 2347 5 720 4308 t
(pared to the equivalent NFS code implementing vnodes and XDR this is tiny.)12 3096 1 720 4428 t
( 5000 lines perform memory management, pro-)6 1906(Of the 18000 lines of code that make up Plan 9, about)11 2164 2 970 4584 t
( for the 17 different file systems imple-)7 1567( rest are)2 317( The)1 206(cess management, hardware interface, and system calls.)6 2230 4 720 4704 t
( file systems are completely self con-)6 1558( most of the)3 508( Since)1 283(menting devices, networks, process control, etc.)5 1971 4 720 4824 t
( working, albeit)2 630( A)1 122( would imply.)2 559(tained, the complexity of the kernel code is even lower than its 18000 lines)13 3009 4 720 4944 t
( can be configured containing only the file systems implementing pipes, a local root,)13 3416(not very useful, kernel)3 904 2 720 5064 t
( of commented C code \(counted using)6 1538( totals 5899 lines)3 693( This)1 232(and a console.)2 576 4 720 5184 t
10 CW f
(wc *.[ch])1 543 1 3787 5184 t
10 R f
( a compari-)2 460(\). As)1 222 2 4358 5184 t
( code \(calculated, we're told, by)5 1367(son, Mach's micro-kernel without device drivers has 25530 lines of C)10 2953 2 720 5304 t
( the same metric our minimal kernel is only 4622 lines long, less than 1/5 the)15 3217( By)1 177(counting semi-colons\).)1 926 3 720 5424 t
( fact, our kernel with every file system included is still less than half the size of their micro-kernel.)18 3938(size. In)1 313 2 720 5544 t
(One might note the similarities between)5 1626 1 970 5700 t
10 CW f
(devtab)2627 5700 w
10 R f
( operating system; the block)4 1155(and parts of the Unix)4 867 2 3018 5700 t
( advantage of Plan 9 is that we)7 1251( One)1 220( vnodes.)1 337(device switch, character device switch, file system switch and)8 2512 4 720 5820 t
(have recognized that these are all essentially the same mechanism and have implemented them as such.)15 4125 1 720 5940 t
10 B f
( Name Space)2 549(3. Virtual)1 436 2 720 6180 t
10 R f
( a terminal or connects to a cpu server, a new process group is created for her pro-)17 3324(When a user boots)3 746 2 970 6336 t
( name space that provides at minimum a root \()9 1928( process group starts with an initial)6 1453(cesses. This)1 511 3 720 6456 t
10 CW f
(/)4645 6456 w
10 R f
(\), some)1 302 1 4738 6456 t
( processor the process is running on \()7 1510(binaries for the)2 608 2 720 6576 t
10 CW f
(/bin/*)2866 6576 w
10 R f
( some local devices \()4 849(\), and)1 255 2 3254 6576 t
10 CW f
(/dev/*)4386 6576 w
10 R f
(\). The)1 266 1 4774 6576 t
( or rearrange their name space using two systems calls,)9 2204(processes in the group can then either add to)8 1790 2 720 6696 t
10 CW f
(mount)4740 6696 w
10 R f
(and)720 6816 w
10 CW f
(bind.)892 6816 w
10 R f
( call is used to attach a new \(not kernel resident\) file system to a point in the name)18 3356(The mount)1 439 2 1245 6816 t
( syntax is)2 378(space. Its)1 396 2 720 6936 t
10 CW f
(mount\(int fd, char *old, int flags, ...\))6 2400 1 970 7092 t
10 R f
(where)720 7248 w
10 I f
(fd)992 7248 w
10 R f
( for a communication stream such as a pipe or a network connection and)13 2956(is a file descriptor)3 730 2 1099 7248 t
10 I f
(old)4815 7248 w
10 R f
(is)4973 7248 w
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10 R f
(- 4 -)2 166 1 2797 480 t
( attach-)1 302( The)1 211( system will be attached.)4 1009(the name of an existing file in the current name space where the file)13 2798 4 720 840 t
(ment creates a new mount device channel whose communication channel is that referred to by)14 3856 1 720 960 t
10 I f
(fd.)4608 960 w
10 R f
(Subse-)4768 960 w
(quent accesses to)2 699 1 720 1080 t
10 I f
(old)1450 1080 w
10 R f
( the com-)2 387(and any files below it in the hierarchy become request messages written to)12 3044 2 1609 1080 t
(munication stream.)1 766 1 720 1200 t
( and also to rearrange)4 890(The bind call is used to attach a kernel resident file system to the name space)15 3180 2 970 1356 t
( syntax is)2 378( Its)1 150(pieces of the name space.)4 1016 3 720 1476 t
10 CW f
(bind\(char *new, char *old, int flags\))5 2220 1 970 1632 t
10 R f
(where)720 1788 w
10 I f
(new)988 1788 w
10 R f
(is a name in the current name space\262 and)8 1640 1 1174 1788 t
10 I f
(old)2839 1788 w
10 R f
(is the same as in mount.)5 961 1 2992 1788 t
( on the)2 284(How the attachment works depends)4 1445 2 970 1944 t
10 I f
(flags)2730 1944 w
10 R f
( possibility is that the old)5 1040( One)1 222(specified in the call.)3 822 3 2956 1944 t
( when both files are directories, Plan 9 allows another possibility.)10 2624( However,)1 441( one.)1 195(file is replaced by the new)5 1060 4 720 2064 t
( that of putting one directory behind the)7 1667( effect is)2 363( The)1 215(The result can be the union of the two directories.)9 2075 4 720 2184 t
( for files contained in the directories, the one in front wins.)11 2349( the case of name conflicts)5 1066(other. In)1 364 3 720 2304 t
10 I f
(Flags)4549 2304 w
10 R f
(speci-)4802 2304 w
( concept is essen-)3 707( This)1 230( in front of, or goes behind the old one.)9 1580(fies whether the new directory replaces, goes)6 1803 4 720 2424 t
( fact, Plan 9 has no)5 790( In)1 139(tially the same as the search paths used in the Unix libraries and the various shells.)15 3391 3 720 2544 t
(search paths and uses these)4 1098 1 720 2664 t
10 I f
(union directories)1 689 1 1846 2664 t
10 R f
( Plan 9 uses the)4 638( a command is executed,)4 996( When)1 291(in their place.)2 552 4 2563 2664 t
(directory)720 2784 w
10 CW f
(/bin)1105 2784 w
10 R f
(the same way Unix uses an execution path.)7 1719 1 1370 2784 t
( process)1 333(The ability to specify the complete name space for a process that contains all resources the)15 3737 2 970 2940 t
( aspect of a process' world can be rearranged.)8 1895( Any)1 231( the basis for a true virtual machine.)7 1499(can access forms)2 695 4 720 3060 t
( can implement part or all of the name space of)10 1909( Processes)1 441( for local ones.)3 602(Remote objects can be substituted)4 1368 4 720 3180 t
( present)1 317( capability is the basis for a number of important services, three of which we)14 3128( This)1 233(other processes.)1 642 4 720 3300 t
(here.)720 3420 w
10 B f
( Cpu Command)2 684(3.1. The)1 367 2 720 3660 t
10 R f
( our terminals, someplace where commands)5 1797(We consider the shared CPU servers as accelerators for)8 2273 2 970 3816 t
( run-)1 192( is important that as little as possible change when)9 2025( It)1 113(can run while maintaining the same environment.)6 1990 4 720 3936 t
( means to make the CPU servers actu-)7 1564( virtual name space provides us with a)7 1563( The)1 210(ning on the CPU server.)4 983 4 720 4056 t
( command,)1 445( A)1 123(ally feel this way to our users.)6 1207 3 720 4176 t
10 CW f
(cpu,)2521 4176 w
10 R f
( daemon process)2 665( A)1 122(calls a CPU server across a network.)6 1466 3 2787 4176 t
( answers the call, creates a new process group for the caller, sets up a name space, and starts a)19 3801(on the server)2 519 2 720 4296 t
( is an analogue of the name space of the call-)10 1795( name space set up)4 752( The)1 206(shell process in the new process group.)6 1567 4 720 4416 t
( screen and the mouse,)4 910( particular, local resources on the terminal, such as the)9 2170( In)1 133(ing process on the terminal.)4 1107 4 720 4536 t
( standard)1 363( The)1 205( terminal.)1 383(become visible to the server processes at the same place in the name space as on the)16 3369 4 720 4656 t
( output, standard error, and current directory of the cpu command become those of the)14 3708(input, standard)1 612 2 720 4776 t
( directories mounted on)3 976( The)1 215(remote shell.)1 526 3 720 4896 t
10 CW f
(/bin)2472 4896 w
10 R f
( that contain executables for the)5 1317(are changed to be those)4 976 2 2747 4896 t
( gen-)1 207( In)1 138( \(the terminal may be a 68020 while a CPU server could be a MIPS\).)14 2824(CPU server's processor type)3 1151 4 720 5016 t
(eral, a user typing the cpu command just notices that things such as compilations speed up while graphics)17 4320 1 720 5136 t
(operations slow down.)2 902 1 720 5256 t
( cpu command)2 592(After the initial handshake to pass information describing the caller's environment, the)11 3478 2 970 5412 t
( server daemon)2 637( The)1 220(becomes a file server answering file system requests from the network connection.)11 3463 3 720 5532 t
( terminal in a standard place,)5 1248(mounts the network connection to the)5 1597 2 720 5652 t
10 CW f
(/mnt/term,)3609 5652 w
10 R f
(and then binds the)3 787 1 4253 5652 t
( example, it binds)3 804( For)1 220( name space.)2 574(resources it decides to keep into the same places in the new)11 2722 4 720 5772 t
10 CW f
(/mnt/term/dev/mouse)720 5892 w
10 R f
(onto)1908 5892 w
10 CW f
(/dev/mouse, /mnt/term/dev/bitblt)1 1909 1 2135 5892 t
10 R f
(onto)4093 5892 w
10 CW f
(/dev/bitblt,)4320 5892 w
10 R f
( driver in the CPU server into file system)8 1643( accesses to those files are converted by the mount)9 2024(etc. Subsequent)1 653 3 720 6012 t
(messages sent to the terminal.)4 1196 1 720 6132 t
8 S1 f
(__________________)720 6680 w
8 R f
( name starting with a ``#'')5 876( Any)1 187(\262 Local kernel resources are referred to by a syntactic escape \(hack\) in the name space.)15 2897 3 720 6780 t
( resource and the remaining characters)5 1232( first character following the ``#'' specifies the type of)9 1751( The)1 167(refers to a local resource.)4 810 4 720 6880 t
( in the name)3 421( to bind the local console to a standard place)9 1492( Thus,)1 229(are a parameter specifying the instance of the resource.)8 1818 4 720 6980 t
(space, one would use)3 677 1 720 7080 t
8 CW f
(bind\("#c", "/dev", FRONT\).)2 1248 1 1445 7080 t
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10 R f
(- 5 -)2 166 1 2797 480 t
10 B f
( Window System)2 717(3.2. The)1 367 2 720 840 t
10 R f
(The user interface is made up of three files:)8 1734 1 970 996 t
10 CW f
(/dev/bitblt)720 1152 w
10 R f
(\261 writes represent bitblt operations to the screen)7 1916 1 1405 1152 t
10 CW f
(/dev/mouse)720 1308 w
10 R f
( return mouse events, i.e., button clicks and movement)8 2181(\261 reads)1 310 2 1345 1308 t
10 CW f
(/dev/cons)720 1464 w
10 R f
(\261 reads return keyboard input, writes put characters to the screen.)10 2604 1 1285 1464 t
( window system, 8.5 [Pik91], offers pro-)6 1701( The)1 218( user.)1 229(Between them, these devices represent all I/O to the)8 2172 4 720 1620 t
( a window is opened, the window system starts a new)10 2239( When)1 298( multiplexed view to these devices.)5 1454(cesses a)1 329 4 720 1740 t
( that process group's name)4 1094( In)1 139( \(usually a shell\) that will run in that window.)9 1881(process group for a command)4 1206 4 720 1860 t
( of)1 108(space, the window system mounts a pipe to itself in front)10 2289 2 720 1980 t
10 CW f
(/dev.)3142 1980 w
10 R f
(Subsequent references by the new pro-)5 1548 1 3492 1980 t
( interprets)1 413( 8.5)1 186( are sent as file system messages to the window server.)10 2303(cess group to any of these devices)6 1418 4 720 2100 t
( 8.5 multiplexes the mouse)4 1079( Similarly,)1 449( screen.)1 305(those requests as accesses of the window instead of the whole)10 2487 4 720 2220 t
( that mouse and keyboard input is available to processes only when their window is)14 3489(and the keyboard so)3 831 2 720 2340 t
(selected.)720 2460 w
( resident user interface will also work inside a)8 1859(The result is that any program written to use the kernel)10 2211 2 970 2616 t
( this is also true of the window system itself, new versions of the window system can be)17 3587(window. Because)1 733 2 720 2736 t
(run and debugged in windows of the current window system.)9 2441 1 720 2856 t
10 B f
( Gateways)1 441(3.3. Network)1 571 2 720 3096 t
10 R f
( a network to which a system is not physically)9 1882(One, sometimes insurmountable, problem is accessing)5 2188 2 970 3252 t
( example, a system may be connected to our Datakit [Fra80] network but not to the DoD)16 3760(attached. For)1 560 2 720 3372 t
( solve this problem by performing protocol to protocol translation.)9 2672( gateways exist that try to)5 1029(Internet. Many)1 619 3 720 3492 t
( order to perform the best)5 1057( In)1 142(Unfortunately, few transport protocols have completely equivalent concepts.)7 3121 3 720 3612 t
( example, TP4 has mes-)4 969( For)1 192( program.)1 391(translation, it is be necessary to know the semantics requested by the)11 2768 4 720 3732 t
( know which)2 534( protocol translator going from TCP to TP4 would not)9 2254( A)1 132(sage delimiters but TCP does not.)5 1400 4 720 3852 t
(bytes correspond to a single write by the sender.)8 1927 1 720 3972 t
( gateway is a file server that serves its own net-)10 1920( A)1 125( a file system.)3 564(In Plan 9, every network interface is)6 1461 4 970 4128 t
( network connects to the gateway)5 1333( process that wants to get at a remote)8 1483( A)1 123(work interfaces to other machines.)4 1381 4 720 4248 t
( the process)2 507( Whenever)1 477( name space.)2 548(and mounts the gateway's interface to the remote network into its)10 2788 4 720 4368 t
( the gateway sees)3 749( Thus,)1 293( request to the gateway.)4 1017(accesses the interface, the mount driver will send the)8 2261 4 720 4488 t
(exactly what the process does.)4 1211 1 720 4608 t
10 B f
( Caching)1 381(4. File)1 286 2 720 4848 t
10 R f
( our termi-)2 437(In building our environment, we've been reluctant to add local disk file systems to any of)15 3633 2 970 5004 t
( Anyone)1 367( first is administration.)3 909( The)1 206( are essentially two reasons for this choice.)7 1727( There)1 284(nals or CPU servers.)3 827 6 720 5124 t
( has unique long term state requires both knowledge and)9 2282( disk that)2 371( Any)1 224(with a local disk must administer it.)6 1443 4 720 5244 t
( lucrative business)2 766( fact, the Bell Labs computer center at Murray Hill is doing a)12 2623( In)1 148(time to administer.)2 783 4 720 5364 t
(maintaining other peoples' disked Sun workstations because the owners have neither the time nor the expe-)15 4320 1 720 5484 t
(rience necessary to do it themselves.)5 1458 1 720 5604 t
( export access to their local file sys-)7 1489( most workstations can)3 940( Although)1 435(The second reason is sharing.)4 1206 4 970 5760 t
( become personified and users)4 1300( Terminals)1 478( individual users, this rarely happens.)5 1605(tems, when left up to)4 937 4 720 5880 t
(become tied to a particular room to do their work.)9 1991 1 720 6000 t
( file systems thanks partially to hardware and partially to caching.)10 2692(Plan 9 survives without local disk)5 1378 2 970 6156 t
( servers transfer at a substantial percentage of memory)8 2193(The CPU servers do so because their links to the file)10 2127 2 720 6276 t
( servers are)2 469( These)1 296( their disk file systems.)4 957( file servers maintain large main memory caches for)8 2134(speed. The)1 464 5 720 6396 t
( main memory to ensure that there is plenty of room for cache.)12 2570(configured with 128 megabytes or more of)6 1750 2 720 6516 t
(Getting a file from a file server is generally faster than it would be to get it from a local disk.)20 3702 1 720 6636 t
( termi-)1 276( Home)1 301( 10 megabit/sec links.)3 893(Office terminals are connected to the file servers by shared 1 or)11 2600 4 970 6792 t
( would)1 276( both cases, the link is much slower than access to a local disk)13 2506( In)1 135(nals use 9600 or 19200 baud links.)6 1403 4 720 6912 t
( keep the caches coherent, we use file identi-)8 1794( To)1 162( performance hit, we use caching.)5 1348( avoid the obvious)3 736(be. To)1 280 5 720 7032 t
( bits identify the file, the)5 1023( 32)1 158( identifiers are unique 64 bit quantities.)6 1616( The)1 214(fiers supplied by the file server.)5 1309 5 720 7152 t
( the file is)3 451( version number is incremented each time)6 1771( The)1 222(other 32 bits identify the version of the file.)8 1876 4 720 7272 t
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(- 6 -)2 166 1 2797 480 t
( it is)2 193( Therefore,)1 477( with the reply.)3 635( time a file is opened the file server returns the identifier)11 2369(modified. Each)1 646 5 720 840 t
(possible to guarantee coherency at each opening of a file.)9 2288 1 720 960 t
( a program terminates, its unmodi-)5 1417( Whenever)1 466(Office terminals only cache pages of executable files.)7 2187 3 970 1116 t
( they are retained until the space is required by)9 1910( Instead)1 343( freed.)1 259(fied text and data pages are not immediately)7 1808 4 720 1236 t
( a program is rerun its executable file is reopened and the current version number)14 3382( When)1 297(other programs.)1 641 3 720 1356 t
( the)1 148( If)1 117( last run, they are reused.)5 1005( the version number has not changed and pages remain from the)11 2575(returned. If)1 475 5 720 1476 t
( most data inten-)3 672( Since)1 273(version number has changed, any remaining pages of the stale version are discarded.)12 3375 3 720 1596 t
( traffic between office terminals)4 1295(sive work is done on the CPU servers, this simple cache saves most of the)14 3025 2 720 1716 t
( caching could be helpful but would require much more complexity.)10 2721( Other)1 277(and the file servers.)3 781 3 720 1836 t
( Therefore,)1 471( for home terminals if it were persistent, but it is not.)11 2151(This cache might also have sufficed)5 1448 3 970 1992 t
( a)1 72( As)1 164( disks to our home terminals to be used as write through caches of the file server files.)17 3484(we have added)2 600 4 720 2112 t
( it needs little)3 569( Therefore,)1 476( servers.)1 341(write through cache, it contains no state that isn't duplicated on the file)12 2934 4 720 2232 t
( the code discovers a disk problem, it reformats the disk)10 2333( If)1 126( a local file system.)4 814(maintenance compared to)2 1047 4 720 2352 t
( she can request)3 658( the user should suspect that the cache is contaminated,)9 2265( If)1 123(discarding the current contents.)3 1274 4 720 2472 t
( refills the cache but no)5 939( system slows down until subsequent use)6 1651( The)1 207(that it be reformatted at the next boot.)7 1523 4 720 2592 t
( not consciously update the disk because the cache uses file identifiers to)12 2942( user need)2 408( The)1 207(information is lost.)2 763 4 720 2712 t
( file is opened, the cache discards any stale data it)10 2087( time a)2 294( Each)1 260(maintain coherency with the file servers.)5 1679 4 720 2832 t
( what she needs to the disk because it is done as a)12 2064( user doesn't have to copy)5 1075( The)1 211(might have for that file.)4 970 4 720 2952 t
(consequence of her using the data.)5 1374 1 720 3072 t
( cache is implemented by a process that resides between the kernel and the file server)15 3465(The disk based)2 605 2 970 3228 t
( It)1 114( can with data cached on the disk.)7 1368( every read request, the process satisfies as much as it)10 2182(connection. For)1 656 4 720 3348 t
( the cache)2 402( When)1 290( through it is saved on the disk.)7 1264( new data that passes)4 841( Any)1 223(gets the rest from the file server.)6 1300 6 720 3468 t
( is limited to)3 528( amount of data cached for any one file)8 1634( The)1 214(fills up the least recently used file is discarded.)8 1944 4 720 3588 t
(1.75 megabytes to prevent one file from displacing all others.)9 2455 1 720 3708 t
( opened, it provides slightly)4 1154(Because the disk based cache only checks for coherency when a file is)12 2916 2 970 3864 t
( coherency)1 437( looser)1 273( This)1 232(different semantics than that seen on office terminals which do not cache data files.)13 3378 4 720 3984 t
( far)1 136( Thus)1 251( via files to ensure an open between each transaction.)9 2131(constraint forces programs that communicate)4 1802 4 720 4104 t
(we have not had to change any programs because of it.)10 2186 1 720 4224 t
10 B f
(5. Conclusion)1 604 1 720 4464 t
10 R f
( the)1 157( Both)1 254(We have presented a distributed system that is simple in structure and flexible in its use.)15 3659 3 970 4620 t
( group name space and a single)6 1337(flexibility and simplicity are the result of two properties, a per process)11 2983 2 720 4740 t
( with some minimal caching we provide a simple system that is as usable at)14 3174( Coupled)1 400(resource interface.)1 746 3 720 4860 t
(home as at work.)3 682 1 720 4980 t
10 B f
(6. Acknowledgements)1 952 1 720 5220 t
10 R f
( would like especially to thank Bart Locanthi, who built)9 2313( We)1 196(Many people helped build the system.)5 1561 3 970 5376 t
( command interpreter)2 877(our terminal, the Gnot, and encouraged us to program it; Tom Duff, who wrote the)14 3443 2 720 5496 t
10 CW f
(rc)720 5616 w
10 R f
( Kowalski, who cheerfully)3 1104(; Tom Killian, who built and programmed the Gnot's SCSI interface; Ted)11 3096 2 840 5616 t
( the software; and Dennis Ritchie, who frequently provided us with much-needed)11 3294(endured early versions of)3 1026 2 720 5736 t
(wisdom.)720 5856 w
10 B f
(References)720 6096 w
10 R f
( ``Datakit\261A Modular Network for Synchronous and Asynchronous Traffic,'' in)9 3240( G. Fraser,)2 427(Fra80. A.)1 405 3 720 6324 t
10 I f
(Proc.)4821 6324 w
(Int. Conf. on Commun.)3 917 1 970 6444 t
10 R f
(, Boston, MA \(June 1980\).)4 1069 1 1887 6444 t
( ``INCON: Network Maintenance and Privacy,'' Internal Memorandum 220106-)8 3367( R. Kalmanek,)2 611(Kal. C.)1 342 3 720 6600 t
( Bell Laboratories.)2 746(0450, AT&T)1 547 2 970 6720 t
( Local Network:)2 674( Metcalfe, D. Boggs, C. Crane, E. Taft, J. Shoch, and J. Hupp, ``The Ethernet)14 3218(Met80. R.)1 428 3 720 6876 t
( Palo Alto Research Centers \(February, 1980\).)6 1852( XEROX)1 394(Three Reports,'' CSL-80-2,)2 1109 3 970 6996 t
( R., ``8.5, The Plan 9 Window System,'')7 1754(Pik91. Pike,)1 512 2 720 7152 t
10 I f
(1991 USENIX Summer Conference Proceedings)4 2010 1 3030 7152 t
10 R f
(\(1991\).)970 7272 w
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10 R f
(- 7 -)2 166 1 2797 480 t
( Pike, ``The Text Editor sam,'')5 1374(Pik87. Rob)1 476 2 720 840 t
10 I f
(Software - Practice and Experience)4 1537 1 2623 840 t
10 B f
(17)4213 840 w
10 R f
( 813-845)1 358(\(11\), pp.)1 369 2 4313 840 t
(\(November 1987\).)1 737 1 970 960 t
( Pike, D. Presotto, K. Thompson, and H. Trickey, ``Plan 9 from Bell Labs,'' in)14 3147(Pik90. R.)1 401 2 720 1116 t
10 I f
(UKUUG Proceed-)1 746 1 4294 1116 t
(ings of the Summer 1990 Conference)5 1479 1 970 1236 t
10 R f
(, London, England \(July, 1990\).)4 1277 1 2449 1236 t
( Presotto, ``Plan 9 from Bell Labs - The Network,'' in)10 2258(Pre88. D.)1 405 2 720 1392 t
10 I f
( of the Spring 1988)4 811(EUUG Proceedings)1 811 2 3418 1392 t
(Conference)970 1512 w
10 R f
(, London, England \(April, 1988\).)4 1321 1 1430 1512 t
( Quinlan, ``A Cached WORM File System,'')6 1798(Qui. S.)1 331 2 720 1668 t
10 I f
(Software \261 Practice and Experience)4 1442 1 2874 1668 t
10 R f
(, p. To appear.)3 576 1 4316 1668 t
( Circuit Design,'' Internal Memorandum 52413-)5 1986( C. Restrick, ``INCON Wire Interface Integrated)6 1992(Res. R.)1 342 3 720 1824 t
( Bell Laboratories.)2 746(860314-01TM, AT&T)1 930 2 970 1944 t
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