Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition

Chapter 2: Operating-System Structures

T. Yang, 2012Partially based on the OSCE text book

Chapter 2: Operating-System Structures

Operating System Services & User OS Interface

System Calls System Programs (System utilities) Operating System Design and

Implementation Virtual Machines

A View of Operating System Services

Linux Layers

Nachos system Layers

Base Operating System (Linux for our class)

Nachos kernel threads

Thread 1 Thread 2 Thread N

Nachos OS modules(Threads mgm, File System, Code execution/memory mapping,

System calls/Interrupt)

Simulated MIPS Machine(CPU, Memory, Disk, Console)

User processUser process

Projects 2&3

Project 1

OS UI: Shell Command Interpreter

OS User Interface: GUI

Programming API – OS System Call

Standard C Library Example

C program invoking printf() library call, which calls write() system call

System Calls System calls: Programming interface to the

services provided by the OS

Mostly accessed by programs via a high-level Application Program Interface (API) rather than direct system call use Three most common APIs are

Win32 API for Windows, POSIX API for POSIX-based systems (including virtually

all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)

Why use APIs rather than system calls?

System Calls System calls: Programming interface to the

services provided by the OS

Mostly accessed by programs via a high-level Application Program Interface (API) rather than direct system call use Three most common APIs are

Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all

versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)

Why use APIs rather than system calls? Portability. Simplicity.

Types of System Calls

Process control File management Device management Information maintenance Communications Protection

Examples of Windows and Unix System Calls

Transition from User to Kernel Mode

Unix I/O CallsfileHandle = open(pathName, flags)

A file handle is a small integer, valid only within a single process, to operate on the device or file

Pathname: a name in the file system. In unix, devices are put under /dev. E.g. /dev/ttya is the first serial port, /dev/sda the first SCSI drive

Flags: read only, read/write, append etc… Mode may be added as the third argument for file

permissionerrorCode = close(fileHandle)

Kernel will free the data structures associated

Unix I/O Calls byteCount = read(fileHandle, buf, count)

Read at most count bytes from the device and put them in the byte buffer buf. Bytes placed from 0th byte.

Kernel can give the process fewer bytes, user process must check the byteCount to see how many were actually returned.

A negative byteCount signals an error (value is the error type)

byteCount = write(fileHandle, buf, count) Write at most count bytes from the buffer buf Actual number written returned in byteCount A negative byteCount signals an error

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Copy file1 to file2#command syntax: copy file1 file2#include <stdio.h>#include <fcntl.h>#define BUF_SIZE 8192void main(int argc, char* argv[]) { int input_fd, output_fd; int ret_in, ret_out; char buffer[BUF_SIZE]; /* Create input file descriptor */ input_fd = open (argv [1], O_RDONLY); if (input_fd == -1) { printf ("Error in openning the input file\n"); return; }

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copy file1 file2 /* Create output file descriptor */ output_fd = open(argv[2], O_WRONLY | O_CREAT, 0644); if(output_fd == -1){ printf ("Error in openning the output file\n"); return; } /* Copy process */ while((ret_in = read (input_fd, &buffer, BUF_SIZE)) > 0){ ret_out = write (output_fd, &buffer, ret_in); if(ret_out != ret_in){ /* Write error */ printf("Error in writing\n"); } } close (input_fd); close (output_fd);}

System Programs/Utilities Categories of System programs/utilities

Process status and management File /directory manipulation File modification and text processing Programming language support (compilers) Program loading and execution Communications Application programs

Most users’ view of the operation system is defined by system programs, not the actual system calls

Linux Utility Programs

OS Design & Implementation

Start by defining goals and specifications

Affected by Choice of hardware User goals –

convenient to use, easy to learn, reliable, safe, and fast

System goals – easy to design, implement, and

maintain, as well as flexible, reliable, error-free, and efficient

OS Design Principles

Separate policy (what to do) and mechanism (how to do) Why?

Layered structure Modular Monolithic kernel vs.

Microkernel

Maximize flexibility

Layered Approach The operating system is divided into a

number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

MS-DOS: Simple Layer Structure

written to provide the most functionality in the least space

Traditional UNIX System Structure

Modular approach Object-oriented Each core component is separate Each talks to the others over known

interfaces Each is loadable as needed within the kernel

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Monolithic Kernel vs. Microkernel

Microkernel System Structure Moves as much from the kernel into “user” space Communication takes place between user modules

using message passing

Benefits: Easier to extend a microkernel Easier to port the operating system to new

architectures More reliable (less code is running in kernel mode) More secure

Weakness: Performance overhead of user space to kernel

space communication

Mac OS X Structure

Virtual Machines

A virtual machine takes the layered approach

A virtual machine provides an interface identical to the underlying bare hardware.

The host creates the illusion that each guest has its own processor and virtual memory/storage.

Virtual Machines (Cont.)

(a) Non-virtual machine (b) virtual machine

VMware Architecture

The Java Virtual Machine

New OS Interface for Applications

Google Android

Microsoft WindowsPhone 7 Apple iOS

Application Store Android MarketApp Marketplace AppStore

User InterfaceJava Application Framework Silverlight Cocoa

Browser WebkitInternet Explorer Webkit

3D Graphics OpenGL DirectX OpenGL

Main programming language Java C# Objective-C

Virtual machine Dalvik VM CLR None

Android (Linux-based)

Apple iOS

Unix-based