operating system lec 2

8/18/2019 Operating System Lec 2

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OPERATING SYSTEM LEC

2


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System Call

Provides the interfae !et"een a #roess and the OS

It is an instr$tion that %enerates an interr$#t that a$ses OS to %ain ontrol

of #roessor&

Proess re'$est ation !y OS&


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System Calls

Interfae !et"een r$nnin%

#ro%ram and the OS&

◦ Assem!ly lan%$a%e instr$tions

(maros and s$!ro$tines)

◦ Some hi%her level lan%$a%es

allo" system alls to !e made

diretly (e&%& C)

Passin% #arameters !et"een a

r$nnin% #ro%ram and OS via

re%isters* memory ta!les or

sta+&

,ni- has a!o$t .2 system alls

◦ read()* "rite()* o#en()* lose()*

for+()* e-e()* iotl()*/&&


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Ty#es of System Calls

Proess ontrol0 end1a!ort* load1e-e$te* reate1terminate* "ait for event ile mana%ement0 reate* delete* o#en lose* %et file attri!$tes 3evie mana%ement0 re'$est* release* read* "rite* %et1set devie

attri!$tes* attah* detah& Info maintenane0 time* date Comm$niation0o#en onnetion* lose onnetion


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Ma4or om#onents

Proess mana%ement Memory mana%ement I1O Seondary Stora%e ile System Protetion Ao$ntin%

Shell (OS ,I) G,I Net"or+in%


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Proess Mana%ement

A #roess is a #ro%ram in e-e$tion&

A #roess needs ertain reso$res s$h as CP,* memory *

files and I1O&

These reso$res are %iven "hen a #roess is reated

5hen the #roess terminates* OS relaims the reso$res

Pro%ram0 #assive

Proess0ative

At most one instr$tion is e-e$ted on !ehalf of a #roess


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Proesses

Scheduler 6 Maintains a reord

of the #roesses&

Adds ne" #roesses "hen

la$nhed&

Removes old #roesses "hen

om#leted&

,ses a #roess ta!le& Process Table 6 Information

a!o$t eah #roess inl$din%7

Main memory ells (RAM)

Priority

R$nnin% or "aitin% (in#$t

from $ser or savin% to dis+) Ri+ Gra8iani%ra8iani9a!rillo&ed$

7


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:ie"in% #roesses "ith Mirosoft 5indo"s

Tas+ ;ar 6 Ri%ht0li+* Tas+ Mana%er

Endin% a #roess 6 Killing the process Ri+ Gra8iani%ra8iani9a!rillo&ed$

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Proesses Dispatcher 0 Oversees the

e-e$tion of eah #roess !y theCP,&

Gives eah #roess a time slie of

CP, time&

Chan%es !et"een #roesses&

Ri+ Gra8iani%ra8iani9a!rillo&ed$

9


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Proess mana%ement

The OS is res#onsi!le for◦ Create $ser1 system #roesses

◦ 3eletin% $ser1system #roesses

◦ Alloatin% hard"are reso$res to a #roess&

◦ Proess omm$niation

◦ 3eadlo+ handlin%

◦

S$s#end a #roess◦ Res$me a #roess

◦ Clone a #roess

◦ Inter0#roess omm$niation

◦ Inter0#roess synhroni8ation

◦ Create 1 delete a hild #roess


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Memory Mana%ement

Conerned "ith the mana%ement of #rimary memory

5hih #art s !ein% $sed

5hih #roesses are to !e loaded

Alloation tehni'$es

3e0alloation tehni'$es


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ile Mana%ement

A file is a lo%ial olletion of information

OS #rovides a lo%ial vie"

OS reate* deletes files

OS ma#s files onto seondary stora%e

Creatin%1deletin% diretories&

;a+in% $# files


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Seondary stora%e Mana%ement

OS is res#onsi!le for 7

free s#ae mana%ement

Stora%e alloation

3is+ shed$lin%


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I1O Mana%ement

I1O ontroller +ee#s tra+ of the stat$s of the devies ;$fferin%* ahin%* s#oolin% 3evie driver interfae 3rivers0 3evie drivers are the ro$tines that interat "ith s#eifi

devie ty#es7

Ena#s$lates devie s#eifi +no"led%e

E&%& ho" to initiali8e a devie* ho" to re'$est the I1O*

ho" to handle interr$#ts and errors

E&%& SCSI devie drivers* Ethernet ard drivers*

video ard drivers* so$nd ard drivers


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I1O Str$t$re

Synhrono$s I1O

wait instr$tion idles CP, $ntil ne-t interr$#t

no sim$ltaneo$s I1O #roessin%* at most one o$tstandin%

I1O re'$est at a time&

Asynhrono$s I1O

After I1O is initiated* ontrol ret$rns to $ser #ro%ram

"itho$t "aitin% for I1O om#letion&


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Net"or+in%

An OS ty#ially has a !$ilt0in omm$niation infra0str$t$re that

im#lements7 A net"or+ #rotool soft"are sta+

A ro$te loo+$# mod$le to ma# a %iven destinationaddress to a ne-t ho#&

A name loo+$# servie to ma# a %iven name to adestination mahine&


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A particular program that handles thinterpretation of users• commands and helps to manage processes

On some systems, command interpreter may• be a standard part of the OS

On others, its just not privileged code that• provides an interface to the user

On others there may be no command language

Command inter#reter (she


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•Keeps track of resource usage

•Both to enforce quotas “youreover the disk limit!"

Accounting


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Protetion

Proessor #rotetion

Protetion mehanisms are im#lement in OS to s$##ort se$rity #oliies&

The %oal of se$rity system is to a$thentiate and a$thori8e&


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3$al Mode

Gives #rotetion or shared reso$res ,ser mode* #rivile%ed mode A mode !it is added to the hard"are to indiate the mode 5ith the mode !it it is #ossi!le to distin%$ish !et"een the modes& On !ootin% $ser #roess starts in $ser mode& If an attem#t is made to e-e$te a #rivile%ed instr$tion in $ser mode the

hard"are tra#s it to the OS&


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3$al0mode o#eration(ont&)

Mode !it added to om#$terhard"are to indiate the

$rrent mode7 monitor(=) or$ser(>)&

5hen an interr$#t or fa$lto$rs* hard"are s"ithes tomonitor mode&

Privile%ed instr$tions only in

monitor mode&

User

Monitor

Set

user

mod

Interrupt/

fault


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3$al0mode o#eration

Sharin% system reso$res re'$ires o#eratin% syste

to ens$re that an inorret #ro%ram annot a$seother #ro%rams to e-e$te inorretly&

Provide hard"are s$##ort to differentiate !et"ee

at least t"o modes of o#eration7

>& ,ser mode 00 e-e$tion done on !ehalf of a $ser&

2& Monitor mode (s$#ervisor1+ernel1system mode) 00

e-e$tion done on !ehalf of o#eratin% system&


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I1O Protetion

All I1O instr$tions are #rivile%ed instr$tions&

M$st ens$re that a $ser #ro%ram o$ld never %ain

ontrol of the om#$ter in monitor mode* for e&%& a

$ser #ro%ram that as #art of its e-e$tion* stores ane" address in the interr$#t vetor&


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Memory Protetion

M$st #rovide memory #rotetion

at least for the interr$#t vetorand the interr$#t serviero$tines&

To #rovide memory #rotetion*add t"o re%isters that determinethe ran%e of le%al addresses a#ro%ram may address&◦ ;ase Re%ister 0 holds smallest

le%al #hysial memory address&◦ Limit re%ister 0 ontains the si8e

of the ran%e&

Memory o$tside the definedran%e is #roteted&

5hen e-e$tin% in monitor mode*the OS has $nrestrited aess to!oth monitor and $sers? memory&

0

256000

3000040

420940

880000

1024000

300

120

Base r

imit re

monitor

!o"1

!o" 2

!o" 4

!o" 3

0


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CP, Protetion

Timer 0 interr$#ts om#$ter after s#eified #eriod to

ens$re that OS maintains ontrol&

Timer is deremented every lo+ ti+&

5hen timer reahes a val$e of =* an interr$#t o$rs&

Timer is ommonly $sed to im#lement time sharin%& Timer is also $sed to om#$te the $rrent time&

Load timer is a #rivile%ed instr$tion&


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O#eratin% Systems7


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OS structure #ts not al$ays clear ho$ to stitch OS modules

together%

MemoryManagement

I/O System

Secondary StorageManagement

File System

Protection System

Accounting System

Process Management

Command Interpreter

Information Services

Error Handling


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Early structure: Monolithic &raditionally, OSs 'like ()#*, +OS $ere built as a

monolithic entity%

everything

user programs

hard$are

OS


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Monolithi 3esi%n

Ma4or Advanta%es7

Cost of mod$le interation is lo"

3isadvanta%es


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Monolithi 3esi%n

Ma4or Advanta%es7 Cost of mod$le interation is lo"

3isadvanta%es


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3esi%n

To# do"n a##roah 6 overall f$ntionality is se#arated into om#onents&

Layered a##roah 6 eah layer $ses servies of lo"er layers& Needs aref$l

definition of eah layer& Layer N is $ser* Layer = is hard"are&

La ered OS Str t re


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Layered OS Str$t$re

OS divided into n$m!er of

layers 0 !ottom layer ishard"are* hi%hest layer is

the $ser interfae&

Eah layer $ses f$ntions

and servies of only lo"er0

level layers&

T


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Layered O#eratin% System


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Mod$les0!ased Str$t$re

Most modern o#eratin% systems im#lement mod$les

,ses o!4et0oriented a##roah

Eah ore om#onent is se#arate

Eah tal+s to the others over +no"n interfaes

Eah is loada!le as needed "ithin the +ernel

Overall* similar to layers !$t "ith more fle-i!le

O-./A)0 S1S&.2h i


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O-./A)0 S1S&.2O3./3#.4

5haracterist

#nterrupts%• #nterrupt transfers control to the interrupt service routine genera

through the interrupt vector , $hich contains the addresses ofthe service routines"

• #nterrupt architecture must save the address of the interrupinstruction"

• #ncoming interrupts are disabled $hile another interrupt is beprocessed to prevent a lost interrupt "

• A trap is a soft$are6generated interrupt caused either by an eor a user request"

• An operating system is interrupt driven"

O-./A)0 S1S&.2 St


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:ery fast stora%e is very e-#ensive& So the O#eratin% System mana%es a hierarhy ofstora%e devies in order to ma+e the !est $se of reso$res& In fat* considerable effo%oes into this s$##ort&

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O-./A)0 S1S&.2O3./3#.4

Storage7ierarchy

8ast and .9pensive

Slo$ an 5heap

:irt$al Mahines


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:irt$al Mahines

Lo%ially treats hard"ar

and OS +ernel ashard"are

Provides interfaeidential to $nderlyin%!are hard"are&

Creates ill$sion ofm$lti#le #roesses 0 ea"ith its o"n #roessorand virt$al memory

#ard$are

%irtual maine

'ernel 'ernel 'ernel

pro&esses

pro&esses

pro&esses

operating system lec 2

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