chap03 from OSD Crowley

7/25/2019 chap03 from OSD Crowley

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01/29/16 Crowley OS Chap. 3 1

The Operating System Interface

Chapter 3


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ey concepts in chapter 3

!System calls

! "ile an# I/O system

$hierarchical file naming

$file interface% open& rea#& write& lsee'& close

$file (ers)s open file

$#e(ices as files *in naming an# in interface+

! ,rocess$operations% create& e-it& wait

! Shell


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The OS e(el Str)ct)re

*chapters 20+

*chapter 3+

*chapter 2+


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01/29/16 Crowley OS Chap. 3

System calls

! special machine instr)ction

$that ca)ses an interr)pt

$(ario)s names% syscall& trap& s(c

! s)ally not generate# 4y 5s

$4)t in assem4ly lang)age f)nctions


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System call flow of control


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5ierarchical file naming systems

! tree of #irectories an# files

$#irectory% contains file an# #irectory names

! O4ects *files an# #irectories+ are name#with path names

$later% other 'in#s of o4ects *e.g. #e(ices+

! ,ath names contains a component name foreach #irectory in the path


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"ile an# I/O system calls

! int open*char name& int flags+

! int rea#*int fi#& char 4)ffer& int co)nt+

! int write*int fi#& char 4)ffer& int co)nt+

! int lsee'*int fi#& int offset& int from+

! int close*int fi#+! int )nlin'*char name+


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Steps in )sing a file


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"iles (ers)s open files

! File% passi(e container of 4ytes on #is'

! Open file% acti(e so)rce *or sin'+ of 4ytes in

a r)nning program

$)s)ally connecte# to a file

$4)t can 4e connecte# to a #e(ice or another

process


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"iles an# open files


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OS o4ects an# operations


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"ile copy enum { Reading=0, Writing=1, ReadAndWrite=2,

ReadWriteFile=0644 };

void FileCop! "#ar $ %romFile, "#ar $ toFile & { int %romF' = open! %romFile, Reading &;

i%! %romF' ( 0 & {

"err (( )*rror opening ) (( %romFile (( endl;

return; }

int toF' = "reat! toFile, ReadWriteFile &;

i%! toF' ( 0 & {

"err (( )*rror opening ) (( toFile (( endl; "lo+e! %romF' &; return; }

#ile! 1 & {

"#ar "#; int n = read! %romF', -"#, 1 &;

i%! n (= 0 & .rea/;

n = rite! toF', -"#, 1 &;

i%! n ( 0 & { "err (( )*rror riting ) (( toFile (( endl;

return; }

}

"lo+e! %romF' &; "lo+e! toF' &;

}


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"ile re(erse *1 of 2+ enum { Reading=0, Writing=1, ReadAndWrite=2 };

enum {ee/Fromeginning=0,ee/FromCurrent=1,ee/From*nd=2};

void Rever+e! "#ar $ %romFile, "#ar $ revFile & {

int %romF' = open! %romFile, Reading &; i%! %romF' ( 0 & {

"err (( )*rror opening ) (( %romFile (( endl;

return;

}

move t#e internal %ile pointer +o t#e ne3t "#ara"ter

read ill .e t#e la+t "#ara"ter o% t#e %ile

int ret l+ee/! %romF', 1, ee/From*nd &;

i%! ret ( 0 & {

"err (( )*rror +ee/ing on ) (( %romFile (( endl;

"lo+e! %romF' &;

return;

}

int revF' = "reat! revFile, 0 &; i%! revF' ( 0 & {

"err (( )*rror "reating ) (( revFile (( endl; "lo+e! %romF' &;

return;

}


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"ile re(erse *2 of 2+ #ile! 1 & {

"#ar "#;

int n = read! %romF', -"#, 1 &; i%! n ( 0 & {

"err (( )*rror reading ) (( %romFile (( endl;

return;

}

n = rite! revF', -"#, 1 &;

i%! n ( 0 & {

"err (( )*rror riting ) (( revFile (( endl; return;

}

e3it t#e loop i% l+ee/ return+ an error5

#e e3pe"ted error i+ t#at t#e "omputed o%%+et ill

.e negative5

i%! l+ee/!%romF', 2, ee/FromCurrent& ( 0 &

.rea/;

}

"lo+e! %romF' &;

"lo+e! revF' &;

}


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:e(ersing a file


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;esign techni


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>eta#ata

! >eta#ata #escri4es the file rather than

4eing the #ata in file itself$also calle# metainformation

! ?-amples of meta#ata

$@ho owns the file$@ho can )se the file an# how

$@hen the file was create#& last )se#& last

mo#ifie#! int stat*char name& StatInfo statInfo+

$this calls ret)rns the file meta#ata


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Aaming OS o4ects

! "ile naming system names files *an#

#irectories+

$4)t why limit it to that

! Other OS o4ects nee# names%

$processes

$#e(ices

$I,C% message


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>apping names to o4ects


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;e(ices as files

! ;e(ices are name# as files

$they can 4e opene# as files& to create open files

$they can 4e )se# as 4yte streams% so)rces of4ytes an# sin's for 4ytes

! ?-amples

$copy some"ile /#e(/tty17$copy a"ile /#e(/tape01


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The process concept

! Program% a static& algorithmic #escription&consists of instr)ctions

7 int main!& {

int i, prod=1;

%or!i=0; i(100; 88i& prod = prod$i;

}

! Process% #ynamic& consists of instr)ctione-ec)tions


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Simple create process void Create9ro"e++1! void & {

int pid1 = impleCreate9ro"e++! )"ompiler) &;

i%! pid1 ( 0 & {

"err (( )Could not "reate pro"e++ :)"ompiler:)

(( endl;

return; }

int pid2 = impleCreate9ro"e++! )editor) &;

i%! pid2 ( 0 & { "err (( )Could not "reate pro"e++ :)editor:)

(( endl;

return; }

Wait until t#e are .ot# "ompleted5

impleWait! pid1 &;

impleWait! pid2 &; )"ompiler) and )editor) al+o end . ma/ing

imple*3it ++tem "all+

imple*3it!&;

}


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,rocess system calls

! int Create,rocess*

char progAame& int argc& char arg(B +

$progAame is the program to r)n in the process

$ret)rns a process i#entifier *pi#+

! (oi# ?-it*int ret)rnCo#e+

$e-its the process that e-ec)tes the e-it system

calls

! int @ait*int pi#+

$waits for a chil# process to e-it

C t


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Create process void Create9ro"e++2! void & {

+tati" "#ar $ arg.

= { )"ompiler), )%ileoCompile), !"#ar $& 0 };

int pid1 = Create9ro"e++! )"ompiler), , arg. &;

i%! pid1 ( 0 & {


(( endl;

return;

}

"#ar $ argv;

argv = )editor); argv = )%ileo*dit);

argv = !"#ar $& 0;

int pid2 = Create9ro"e++! )editor), , argv &;

i%! pid2 ( 0 & {


(( endl;

return;

}

!void& Wait! pid1 &;

!void& Wait! pid2 &;

*3it! 0 &;

}


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5ow arg)ments are passe#


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,rint arg)ments #i+ program rite+ out it argument+5

?in"lude (io+tream5#@

void main! int arg", "#ar $ argv< > & {

int i;

%or! i = 0; i ( arg"; 88i & {

"out (( argv (( ) );

}

"out (( ):n);

}


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process hierarchy


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Interprocess comm)nication

*I,C+

! >any metho#s ha(e 4een )se#% messages&

pipes& soc'ets& remote proce#)re call& etc.

! >essages an# message


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?-ample of

message passing paths


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>essage passing system calls

! int Create>essageD)e)e* (oi# +

$ret)rns a message


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>essage% file sen#er *1 of 2+

void end+go! int m+gBBid, int m+g0=0, int

m+g1=0, int m+g2=0 & { int m+g;

m+g = m+g0; m+g = m+g1; m+g = m+g2;

!void&ende++age! m+gBBid, m+g &;

}

enum { Reading=0, Writing=1, ReadAndWrite=2 };

enum{ FileoEpen=1, endueue=2, Re"eiveueue= };void main! int arg", "#ar $ argv< > & {

int %romF' = open! argv, Reading &;

i%! %romF' ( 0 & {

"err (( )Could not open %ile

(( argv (( endl;

e3it! 1 &; }

int toB = atoi!argv&;

> fil # *2 f 2+


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>essage% file sen#er *2 of 2+ #ile! 1 & {

"#ar "#;

int n = read! %romF', -"#, 1 &; i%! n (= 0 &

.rea/;

end+go! toB, "# &;

}

"lo+e! %romF' &;

end+go! toB, 0 &;

int m+g;

int %romB = atoi!argv


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>essage% file recei(er enum{ endueue=1, Re"eiveueue=2 };


+tart t#e "ount at Gero5 int "ount = 0;

int m+g;

int %romB = atoi!argv&;

#ile! 1 & {

Re"eivee++age! %romB, m+g &;

i%! m+g == 0 &

.rea/;

An me++age it# nonGero "ontent

i+ a "#ara"ter to "ount5

88"ount;

} end t#e "ount .a"/ to t#e +ender5

int toB = atoi!argv t t *1 f 2+


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>essage% start processes *1 of 2+ int Create9ro"e++Wit#Arg+!"#ar $ progBname,

"#ar $ arg1=0, "#ar $ arg2=0, "#ar $ arg=0& {

"#ar $arg+;

arg+ = progBname;

arg+ = arg1;

arg+ = arg2;

arg+ = arg;

arg+ = 0;

int arg" = 4; i%! arg == 0& arg";

i%! arg2 == 0& arg";

i%! arg1 == 0& arg";

return Create9ro"e++! progBname, arg", arg+ &;

}

"#ar $ itoa! int n & { "#ar $ re+ult = ne "#ar;

+print%! re+ult, )Id), n &;

return re+ult;

}

> t t *2 f 2+


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>essage% start processes *2 of 2+ void main! int arg", "#ar $ argv< > & {

Create t#e me++age ueue+ t#e pro"e++e+ ill u+e5

int 1 = Createe++ageueue!&;

int 2 = Createe++ageueue!&;

Create t#e to pro"e++e+, +ending ea"# t#e

identi%ier %or t#e me++age ueue+ it ill u+e5

int pid1 = Create9ro"e++Wit#Arg+! )Fileend),

)Fileoend), itoa!1&, itoa!2& &;

int pid2 = Create9ro"e++Wit#Arg+! )FileRe"eive), itoa!1&, itoa!2& &;

Wait %or t#e to pro"e++e+ to "omplete5

int ret1 = ait! pid1 &;


We do not u+e t#e return "ode ret1 and ret2

in t#i+ e3ample5 'e+tro t#e me++age ueue+5

'e+troe++ageueue! 1 &;

'e+troe++ageueue! 2 &;

*3it! 0 &;

}


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O4ects for

sen#ing a file with messages


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AIEstyle process creation

!int for'*+$creates an e-act copy of the calling process

! int e-ec(*char progAame& char arg(B +

$r)ns a new program in the calling process$#estroying the ol# program

! int e-it*int retCo#e+

$e-its the calling process! int wait*int retCo#e+

$waits for any e-ite# chil#& ret)rns its pi#


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AIE for'

C t *AIE t l +


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Create process *AIEstyle+ void Create9ro"e++! void & {

int pid1, pid2;

"#ar $argv = {)"ompiler), )%ileoCompile), 0}; pid1 = %or/!&;

i%! pid1 == 0 & { C#ild pro"e++ "ode .egin+ #ere

e3e"v! )"ompiler), argv &; e3e"ute "ompiler

C#ild pro"e++ "ode end+ #ere5

e3e"v doe+ not return

} 9arent e3e"ute+ #ere .e"au+e pid1 J= 0

argv = )editor);

argv = )%ileo*dit);

argv = 0;

i%! !pid2 = %or/!&& == 0 &

e3e"v! )editor), argv &;int reta, ret.;

int pida = ait! -reta &;

int pid. = ait! -ret. &;

}


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Stan#ar# inp)t an# o)tp)t

! >ost programs are filters%

$one inp)t stream *stan#ar# inp)t+

$some processing

$one o)tp)t stream *stan#ar# o)tp)t+

! So the OS starts a program o)t with two open

files& stan#ar# inp)t an# stan#ar# o)tp)t

grep #elveti"a (%ontKi+t @#elvKi+t


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:e#irection of stan#ar# inp)t an#

o)tp)t


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,ipes

! ,ipe% another I,C mechanism

$)ses the familiar file interface

$not a special interface *li'e messages+

! Connects an open file of one process to an

open file of another process

$Often )se# to connect the stan#ar# o)tp)t of

one process to the stan#ar# inp)t of another

process


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>essages an# pipes compare#

,i fil #


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,ipe% file sen#er enum { Reading=0, Writing=1, ReadAndWrite=2 };


int %romF' = open! argv, Reading &; int toBpipe = open! argv, Writing &;

#ile! 1 & {

"#ar "#;

int n = read! %romF', -"#, 1 &;

i%! n == 0 & .rea/;

rite! toBpipe, -"#, 1 &;

}

"lo+e! %romF' &;

"lo+e! toBpipe &;

int n, %romBpipe = open! argv, Reading &;

int n i+ %our .te+ long, +o e read %our .te+

read! %romBpipe, -n, 4 &;

"lo+e! %romBpipe &;

"out (( n (( ) "#ara"ter+:n);

e3it! 0 &;

}

,i fil i


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,ipe% file recei(er enum { Reading=0, Writing=1, ReadAndWrite=2 };


int "ount = 0; #e %ir+t argument i+ t#e pipe to read %rom5

int %romBpipe = open! argv, Reading &;

#ile! 1 & {

"#ar "#;

int n = read! %romBpipe, -"#, 1 &;

i%! n == 0 &

.rea/;

88"ount;

}

"lo+e! %romBpipe &;

+end t#e "ount .a"/ to t#e +ender5 int toBpipe = open! argv, Writing &;

rite! toBpipe, -"ount, 4 &;

"lo+e! toBpipe &;

e3it! 0 &;

}

,i t


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,ipe% create processes void main! int arg", "#ar $ argv< > & {

int pid1 = Create9ro"e++Wit#Arg+!)Fileend),

)Fileoend), )9ipeoRe"eiver), )9ipeoender)&; int pid2 = Create9ro"e++Wit#Arg+! )FileRe"eive),

)9ipeoRe"eiver), )9ipeoender) &;



e3it! 0 &;

}


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>ore on naming

! @e ha(e seen three naming systems$Global character namesin the file system%

name# pipes

$Process-local names*file i#entifiers+%

anonymo)s pipes

$Global integer namespic'e# 4y the OS%

message


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;esign techni


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OS e-amples

! AIE *TT& Fell a4s+$Fasis of most mo#ern OSes

! >ach *C>+

$>icro'ernel$:esearch system& now wi#ely )se#

! >S/;OS *>icrosoft+

$Aot a f)ll OS

OS l


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>ore OS e-amples

! @in#ows AT *>icrosoft+$S)ccessor to >S/;OS

! OS/2 *IF>+

! >acintosh OS *pple+$Inno(ations in the GI

$To 4e replace# 4y :hapso#y *>ach+


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Shell% an OS interface

! Interacti(e access to the OS system calls

$copy from"ile to"ile

!Contains a simple programming lang)age

! ,op)lari=e# 4y AIE

$Fefore AIE% HC& OS Cs *comman#

lang)ages+

$Fo)rne shell& C shell *csh+& orn shell *'sh+&

Fo)rneagain shell *4ash+& etc.


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Two (iews of a shell

Shell% glo4als


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Shell% glo4als ?in"lude (io+tream5#@

+ome "on+tant+

ma3imum +iGe o% an one argument"on+t int ARLMN* H0

ma3imum num.er o% argument+

"on+t int OARL 20

to/en tpe+ returned . getWord!&

"on+t int RMOL 1

"on+t int MOR*'MR 2

"on+t int EPR*'MR

"on+t int O*WKMO* 4

de%ine t#e argv +tru"ture

"#ar $argv; +pa"e %or argv ve"tor

"#ar arg+; +pa"e %or argument+

Shell *1 of 3+


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Shell *1 of 3+ void main! int arg"ount, "#ar $argument+< > & {

int a+MnRedir, a+EutRedir;

"#ar inRedir, outRedir; ea"# iteration ill par+e one "ommand

#ile! 1 & {

di+pla t#e prompt

"out (( )Q );

o %ar e #ave not +een an redire"tion+

a+MnRedir = 0;

a+EutRedir = 0; et up +ome ot#er varia.le+5

int arg" = 0;

int done = 0;

"#ar ord;

Read one line %rom t#e u+er5

#ile! Jdone & { getWord get+ one ord %rom t#e line5

int argpe = getWord!ord&;

getWord return+ t#e tpe o% t#e ord it read

Shell *2 of 3+


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Shell *2 of 3+ +it"#! argpe & {

"a+e MOR*'MR

a+MnRedir = 1;

!void&getWord!inRedir&; .rea/;

"a+e EPR*'MR

a+EutRedir = 1;

!void&getWord!outRedir&;

.rea/;

"a+e RMOL

+tr"p!arg+ = -arg+ = OPKK;

i%! +tr"mp!arg+, )logout)& == 0 &

.rea/;

Shell *3 of 3+


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Shell *3 of 3+ i%! %or/!& == 0 & {

i%! a+MnRedir & {

"lo+e!0&; "lo+e +tandard input

open!inRedir, 0&; reopen a+ redire"t %ile } i%! a+EutRedir & {

"lo+e!1&; "lo+e +tandard output

enum { P+erWrite=0SHH };

"reat!outRedir, P+erWrite&; }

"#ar "md;

+tr"p!"md, )5)&; +tr"at!"md, arg+&; e3e"v!"md, -argv&;

+tr"p!"md, ).in)&; +tr"at!"md, arg+&;

e3e"v!"md, -argv&;

"out (( )C#ild "ould not e3e" :)) (( arg+

(( ):):n);

e3it!1&;

} int +tatu+; !void& ait!-+tatu+&;

}

"out (( )#ell e3iting5:n);

}

;esign techni


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01/29/16 C l OS Ch 3 8

;esign techni& CO:F

! It is )sef)l for a program to ha(e 4oth

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chap03 from OSD Crowley