Introduction to Operating Systems Abstractions Using Plan 9 from Bell Labs

416 Pages·2007·1.26 MB·English

Introduction to Operating Systems Abstractions
Using Plan 9 from Bell Labs
(Draft(cid:20)9/28/2007)
Francisco J Ballesteros

Copyright ©2006 Francisco J Ballesteros
Plan 9 is Copyright ©2002 Lucent Technologies Inc. All Rights Reserved.

Preface
Using effectivelythe operating system is very important for anyone working with computers. It can
be the difference between performing most tasks by hand, and asking the computer to perform them.
Traditionally, Operating Systems courses used UNIX to do this. However, today there is no such
thingasUNIX.Linuxisahugesystem,fullofinconsistencies,withprogramsthatdomultipletasksanddo
not perform them well. Linux manual pages just cannot be read.
These lecture notes use Plan 9 from Bell Labs to teach a first (practical!) course on operating sys-
tems.Thesystemiseasytouse for programmers, and is an excellent example of high-quality system design
andsoftwaredevelopment.Studyingitscoderevealshowsimplicitycanbemoreeffectivethancontortions
made by other systems.
ThefirstOperatingSystemscourseatReyJuanCarlosUniversityisfocusedonpractice.Becausein
theory,theoryis likepractice,but in practiceit is not. Whatisimportantisforyoutousethesystem,and
tolearntosolveproblems. Theorywillcomelatertofillthegapsandtrytogivemoreinsightaboutwhata
system does and how can it be used.
The whole text assumes that you have been already exposed to computer, and used at least a com-
puter running Windows. This is so common that it makes no sense to drop this assumption. Furthermore,
weassumethatyoualreadyknowhowtowriteprograms.Thisisindeedthecaseforthelecturethistextis
writtenfor. Onelastassumptionisthatyouattendedabasiccomputer architecture course, and you know at
least basic concepts. There is a quick review appendix in case you need to refresh your memory.
Throughthetext,theboldfacefontis usedwhenanewconceptis introduced. This will help you to
make quick reviews and to double check that you know the concepts. All important concepts are listed in
the index, at the end of the book. The constant width teletype font is used to refer to machine data,
including functions, programs, andsymbol names.Inmanycases,textin constantwidth fontreproducesa
session with the system (e.g., typing some commands and showing their output). The text written by the
user (and not by the computer) is slightlyslanted, but still in constant width. Note the difference with
respect to the font used for text written by a program, which is notslanted. Italicsare used toemphasize
thingsandtorefertothesystemmanual,likeinintro(1). Regardingnumericvalues,weusetheCnotation
to represent hexadecimal and octal numeric bases.
Unlike inmostothertextbooksforoperatingsystemscourses,bibliographicreferencesarekepttothe
bare minimum. We cite a particular text when we think that it may be worth reading to continue learning
aboutsomethingsaidin this book.So, donot quicklydismiss references.Weencourageyouto readthem,
to learn more. There are not so many ones. If you want to get a thorough set of references for something
discussed in the test, we suggest looking at a more classical operating systems textbook, like for example
[1].
Itis important to notethat this bookis not areferenceforusing anoperatingsystem nor a reference
forPlan9fromBellLabs.Theuser’smanualthatcomesinstalledwithinthesystemistheproperreference
to use. These lecture notes just shows you how things work, by using them. Once you have gone through
the course, you are expected to search and use the user’s manual as a reference.
Onefinalnoteofcaution.Thistextistobereadwithacomputersidebyside.Theonlywaytolearn
to use a system is by actually using it. Reading this without doing so is meaningless.
Iamgratefulgotoothercolleagueswhosufferedorhelpedinonewayoranothertowritethisbook.
First, authors of Plan 9 from Bell Labs made an awesomesystem, worth describing for an Operating Sys-
tems Course. It cannot be overemphasizedhow much help the authors of Plan 9 provide to anyone asking
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questions in the 9fans list. For what is worth, I have to say that I am deeply gratefulto people like Rob
Pike, Dave Presotto, Jim McKie, Russ Cox, and many others. In particular, Russ Cox seems to be a pro-
gram listening for questions at 9fans, at least his response time suggests that. I have learned a lot from
you all (or I tried). Other colleagues from Rey Juan Carlos University helped me as well. Pedro de las
Heras was eager to get new drafts for this manuscript. Sergio Arévalo was an unlimited supply of useful
commentsandfixesforimproving this book,speciallyforusing it asatextbook.JoséCentenowasscared
tohellafterreadingourinitialdescriptionof computer networks, and helped to reach a much better descrip-
tion.
Francisco J. Ballesteros
Laboratorio de Sistemas,
Rey Juan Carlos University of Madrid
Madrid, Spain
2006
Table of Contents
1. Getting started 1
1.1. What is an Operating System? 1
1.2. Entering the system 3
1.3. Leaving the system 6
1.4. Editing and running commands 6
1.5. Obtaining help 8
1.6. Using files 10
1.7. Directories 12
1.8. Files and data 15
1.9. Permissions 18
1.10. Writing a C program in Plan 9 20
1.11. The Operating System and your programs 22
1.12. Where are the files? 24
1.13. The Shell, commands, binaries, and system calls 25
1.14. The Operating System and the hardware 25
2. Programsand Processes 29
2.1. Processes 29
2.2. Loaded programs 31
2.3. Process birth and death 35
2.4. System call errors 40
2.5. Environment 42
2.6. Process names and states 45
2.7. Debugging 47
2.8. Everything is a file! 49
3. Files 55
3.1. Input/Output 55
3.2. Write games 60
3.3. Read games 64
3.4. Creating and removing files 65
3.5. Directory entries 67
3.6. Listing files in the shell 72
3.7. Buffered Input/Output 75
4. Parentand Child 83
4.1. Running a new program 83
4.2. Process creation 84
4.3. Shared or not? 88
4.4. Race conditions 91
4.5. Executing another program 91
4.6. Using both calls 93
4.7. Waiting for children 94
4.8. Interpreted programs 97
5. Communicating Processes 101
5.1. Input/Output redirection 101
5.2. Conventions 106
5.3. Other redirections 106
5.4. Pipes 107
5.5. Using pipes 112
5.6. Notes and process groups 117
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5.7. Reading, notes, and alarms 120
5.8. The file descriptor bulletin board 123
5.9. Delivering messages 125
6. Network communication 135
6.1. Network connections 135
6.2. Names 139
6.3. Making calls 141
6.4. Providing services 144
6.5. System services 150
6.6. Distributed computing 151
7. Resources, Files, and Names 153
7.1. Resource fork 153
7.2. Protecting from notes 155
7.3. Environment in shell scripts 157
7.4. Independent children 158
7.5. Name spaces 159
7.6. Local name space tricks 164
7.7. Device files 166
7.8. Unions 167
7.9. Changing the name space 169
7.10. Using names 170
7.11. Sand-boxing 172
7.12. Distributed computing revisited 174
8. Using the Shell 179
8.1. Programs are tools 179
8.2. Lists 180
8.3. Simple things 183
8.4. Real programs 186
8.5. Conditions 190
8.6. Editing text 193
8.7. Moving files around 198
9. Moretools 201
9.1. Regular expressions 201
9.2. Sorting and searching 205
9.3. Searching for changes 210
9.4. AWK 214
9.5. Processing data 219
9.6. File systems 224
10. Concurrentprogramming 229
10.1. Synchronization 229
10.2. Locks 232
10.3. Queueing locks 239
10.4. Rendezvous 246
10.5. Sleep and wakeup 248
10.6. Shared buffers 252
10.7. Other tools 255
11. Threads and Channels 261
11.1. Threads 261
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11.2. Thread names 264
11.3. Channels 269
11.4. I/O in threaded programs 274
11.5. Many to one communication 277
11.6. Other calls 285
12. UserInput/Output 289
12.1. Console input 289
12.2. Characters and runes 292
12.3. Mouse input 295
12.4. Devices for graphics 298
12.5. Graphics 300
12.6. A graphic slider 303
12.7. Keyboard input 309
12.8. Drawing text 312
12.9. The window system 313
13. Building a File Server 321
13.1. Disk storage 321
13.2. The file system protocol 325
13.3. Semaphores for Plan 9 331
13.4. Speaking 9P 332
13.5. 9P requests 336
13.6. Semaphores 338
13.7. Semaphores as files 341
13.8. A program to make things 349
13.9. Debugging and testing 354
14. Security 357
14.1. Secure systems 357
14.2. The local machine 358
14.3. Distributed security and authentication 359
14.4. Authentication agents 362
14.5. Secure servers 368
14.6. Identity changes 371
14.7. Accounts and keys 374
14.8. What now? 375
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