CS2106 Lec2 Concept

8/8/2019 CS2106 Lec2 Concept

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Lecture 2

OS Conceptsand Structure

17 August, 2010

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Overview of BasicConcepts in OS

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Recall:Time-Sharing

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CPU Memory Disk

Waiting Area

Task 1

Task 2Task 3

Network

...

Task 4

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what do you need to

remember in order toresume a task?

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process:

code + data +context of execution

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example ofprocess-related sys calls:

fork( ) waitpid( ) exec( ) exit( )

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how to prevent one process

from corrupting the memory ofanother process?

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every process has its ownaddress space

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a process may occupy

different physical memorylocation at different time

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but the executable code

remains the same.

(e.g., for instruction:

load from address X to register Ywhat should X be?)

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Memory

stack

data

code

CPU

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Data on disks are organizedinto files and directories

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block special files

character special filesin

/dev

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pipe

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example offile-related sys calls:open( ) close( ) read( ) write( )

lseek( ) state( )

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example offile systems-related sys calls:mkdir( ) rmdir( )

link( ) unlink( )

mount( ) umount( )

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User interfaces to OS:

1. shell2. window systems

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processes

address spacefiles and directories

shell

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Structure of OSes

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Structure ofLinux Kernel

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interrupt dispatcher

system calls

hardware

user program

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system calls

hardware

user program

processmanagement

memorymanagement

I/O component

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system calls

hardware

user program

processmanagement

memorymanagement

device drivers

virtual file sys

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such design is calledmonolithic kernel

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dynamically loadable

kernel modulekeeps the kernel small, extensible

(also in MS Windows, Mac OS X)

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Alternative to monolithic design:microkernel

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system calls

hardware

process managementmemory management

device driversfile systemsnetwork

An example microkernel architecture

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keep minimal functions in kernel

example:

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A brief introduction to

C and programming inUNIX

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#include

#include

voidsay_hello(inttimes)

{

inti;

for(i=0;i


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gcc hello.c

gcc -o hello hello.c

gcc -Wall -g -o hello hello.c

gcc -c hello.c; gcc hello.o

to compile:

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gdb helloto debug:

useful gdb commands:

b c l p r s

where set up down watch display finish

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intx=1;inty=2;

x=y;

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int*x;

inty=2;

x=&y;

*x=3;y=*x;

//whatis*y,&x?

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int*x;

inty=2;

*x=1;

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inty=2;

f(y);

intf(inta)

{a=2;

}

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inty[3];

*y=7;*(y+1)=9

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char*name;

name=malloc(10);

strcpy(name,cs2106);:

:free(name);

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structprocess{

intpid;

char*cmd;

intstatus;}

typedefstructprocessproc;

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proc*create_process(){

proc*p=malloc(sizeof(proc));//initializefieldsreturnp;}

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