Download 2.01 - Kangwon

Silberschatz, Galvin and Gagne ©2006
Operating System Principles
Chapter 2:
Operating-System Structures
Mi Jung Choi
[email protected]
Dept. of Computer Science
Ch2. Operating-System Structures
Chapter 2: Operating-System Structures
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Operating System Services
User Operating System Interface
System Calls
Types of System Calls
System Programs
 Operating System Design and Implementation
 Operating System Structure
 Virtual Machines
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Ch2. Operating-System Structures
Objectives
 To describe the services an operating system provides to
users, processes, and other systems
 To discuss the various ways of structuring an operating
system
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Ch2. Operating-System Structures
To whom: Users, Processes, other systems
Operating System Services
With What: Memory, Storage, Devices, CPU
 One set of OS services provides functions that are helpful to the
user
 Another set of OS functions exists for ensuring the efficient
operation of the system itself via resource sharing
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Ch2. Operating-System Structures
Operating System Services
 One set of OS services provides functions that are helpful
to the user:


User Interface
 Almost all operating systems have a user interface (UI)
 Varies between Command-Line Interface (CLI), Graphical User
Interface (GUI), Batch Interface
Program Execution
 The system must be able to load a program into memory and to
run that program, end execution either normally or abnormally
(indicating error)
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Ch2. Operating-System Structures
Operating System Services
 One set of OS services provides functions that are helpful
to the user:
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
I/O Operations
 A running program may require I/O, which may involve a file or
an I/O device.
File-system Manipulation
 The file system is of particular interest.
 Process needs to
–
–
–
–

read and write files and directories
create and delete them
search them
list file Information
permission management is also required.
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Ch2. Operating-System Structures
Operating System Services
 One set of OS services provides functions that are helpful
to the user:


Communications
 Processes may exchange information, on the same computer
or between computers over a network
 Communications may be via shared memory or through
message passing (packets moved by the OS)
Error Detection
 OS needs to be constantly aware of possible errors
– may occur in the CPU and memory, in I/O devices, in user program


For each type of error, OS should take the appropriate action
to ensure correct and consistent computing
Debugging facilities can greatly enhance the user’s and
programmer’s abilities to efficiently use the system
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Ch2. Operating-System Structures
Operating System Services
 Another set of OS functions exists for ensuring the
efficient operation of the system itself via resource sharing

Resource allocation
 When multiple users or multiple jobs running concurrently,
resources must be allocated to each of them
 Many types of resources
– Some (such as CPU cycles, main memory, and file storage) may have
special allocation code.
– Others (such as I/O devices) may have general request and release code.

Accounting
 To keep track of which users use how much and what kinds of
computer resources
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Ch2. Operating-System Structures
Operating System Services
 Another set of OS functions exists for ensuring the
efficient operation of the system itself via resource sharing

Protection and security in a multi-user computer system
 The owners of information may want to control use of that
information
 Concurrent processes should not interfere with each other


Protection involves ensuring that all access to system
resources is controlled
Security of the system from outsiders requires user
authentication,
– extends to defending external I/O devices from invalid access attempts
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Ch2. Operating-System Structures
User Operating System Interface - CLI
 CLI allows direct command entry

Command Line Interface (CLI)
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
Sometimes implemented in kernel,
Sometimes by systems program
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Sometimes multiple flavors are implemented – shells
 BASH (Bourne-Again SHell ), CSH (C SHell), KSH (Korn
SHell), TCSH on Linux
 CMD on windows XP
Primarily fetches a command from user and executes it
 Sometimes commands built-in,
 Sometimes just names of programs
– adding new features doesn’t require shell modification
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Ch2. Operating-System Structures
User Operating System Interface - GUI
 User-friendly desktop metaphor interface
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Usually mouse, keyboard, and monitor
Icons represent files, programs, actions, etc
Various mouse buttons over objects in the interface cause various
actions
 provide information, options, execute function, open directory
Invented at Xerox PARC
 Many systems now include both CLI and GUI interfaces
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Microsoft Windows is GUI with CLI “command” or “cmd” shell
Apple Mac OS X as “Aqua” GUI interface with UNIX kernel
underneath and shells available
Linux is CLI with optional GUI interfaces (GNOM, KDE)
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Ch2. Operating-System Structures
System Calls
The only way that a process communicate with OS
It provides an interface to the service made available by an OS
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Ch2. Operating-System Structures
System Calls
 Programming interface to the services provided by the OS
 Typically written in a high-level language (C or C++)

Sometimes written using assembly-language instructions.
 Mostly accessed by programs via a high-level Application Program
Interface (API) rather than direct system call use
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Each API consists of one or more systems calls.
APIs are OS specific.
 Three most common APIs are
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Win32 API, Win64 API for Windows,
POSIX API for POSIX-based systems (including UNIX, Linux, Mac OS X)
Java API for the Java virtual machine (JVM)
 Why use APIs rather than system calls?

To provide a simplified method of the use of system calls and hide the
implementation details.
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Ch2. Operating-System Structures
Example of System Calls
 System call sequence to copy the contents of one file to
another file
scanf(infile)
scanf(outfile)
fopen(“r”);
fopen(“w”);
fgetc();
fputc();
fclose(infile);
fclose(outfile);
exit();
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Ch2. Operating-System Structures
Example of Standard API
 Consider the ReadFile() function in the Win32 API
 reads data from a file, and starts at the position that the file pointer
indicates.
 You can use this function for both synchronous and asynchronous
operations.
 A description of the parameters passed to ReadFile()
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hFile - [in] A handle to the file to be read.
lpBuffer - [out] A pointer to the buffer that receives the data read from a file.
nNumberOfBytesToRead - [in] The maximum number of bytes to read.
lpNumberOfBytesRead - [out] A pointer to the variable that receives the
number of bytes read.
lpOverlapped - [in] A pointer to an OVERLAPPED structure.
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Ch2. Operating-System Structures
System Call Implementation
 Typically, a number associated with each system call
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System-call interface maintains a table indexed according to these
numbers
The system call interface invokes intended system call in OS
kernel and returns status of the system call and any return values
 The caller needs to know nothing about how the system
call is implemented


Just needs to obey API and understand what OS will do as a result
of the call
Most details of OS interface hidden from programmer by API
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Ch2. Operating-System Structures
API – System Call – OS Relationship
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Ch2. Operating-System Structures
Standard C Library Example
 C program invoking
printf() library call,
which calls
write() system call
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Ch2. Operating-System Structures
System Call Parameter Passing
 Often, more information is required than simple identity of
desired system call
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Exact type and amount of information vary according to OS and
system call
 Three general methods used to pass parameters to the OS
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Simplest: pass the parameters in registers
 In some cases, may be more parameters than registers
Parameters stored in a block, or table, in memory, and address of
block passed as a parameter in a register
 This approach taken by Linux and Solaris
Parameters placed, or pushed, onto the stack by the program and
popped off the stack by the operating system
Block and stack methods do not limit the number or length of
parameters being passed
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Ch2. Operating-System Structures
Parameter Passing via Table
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Ch2. Operating-System Structures
Types of System Calls
 Five types of system calls
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Process control
File management
Device management
Information maintenance
Communications
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Ch2. Operating-System Structures
Types of System Calls
 Process control
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end, abort
load, execute
create process, terminate process
get process attributes, set process attributes
wait for time
wait event, signal event
allocate and free memory
 File management
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create file, delete file
open, close
read, write, reposition (move, rename, etc.)
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Ch2. Operating-System Structures
Types of System Calls
 Device management
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request device, release device
read, write, reposition
get device attributes, set device attributes
logically attach or detach devices
 Information maintenance
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get time or date, set time or date
get system data, set system data
get process, file, or device attributes
set process, file, or device attributes
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Ch2. Operating-System Structures
Types of System Calls
 Communications
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Create, delete communication connection
send, receive messages
transfer status information
attach or detach remote devices
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Ch2. Operating-System Structures
MS-DOS execution
(a) At system startup (b) running a program
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Ch2. Operating-System Structures
FreeBSD Running Multiple Programs
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Ch2. Operating-System Structures
System Programs
 System programs provide a convenient environment for
program development and execution.

Some of them are simply user interfaces to system calls; others
are considerably more complex
 They can be divided into:
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


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File manipulation
Status information
File modification
Programming language support
Program loading and execution
Communications
 Most users’ view of the operation system is defined by
system programs, not the actual system calls
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Ch2. Operating-System Structures
System Programs
 File management
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create, delete, copy, rename, print, dump, list, and generally
manipulate files and directories
 Status information
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Some programs ask the system for info.
 date, time, amount of available memory, disk space, number of
users.
 detailed performance, logging, and debugging information.
Typically, these programs format and print the output to the
terminal, other output devices, files.
Some systems implement a registry - used to store and retrieve
configuration information.
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Ch2. Operating-System Structures
System Programs (cont’d)
 File modification
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Text editors to create and modify files
Special commands to search contents of files or perform
transformations of the text
 Programming-language support

Compilers, assemblers, debuggers and interpreters sometimes
provided
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Ch2. Operating-System Structures
System Programs (cont’d)
 Program loading and execution
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
Once a program is assembled or compiled, it must be loaded into
memory to be executed.
Absolute loaders, re-locatable loaders, linkage editors, and
overlay-loaders, debugging systems for higher-level and machine
language
 Communications
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
provide the mechanism for creating virtual connections among
processes, users, and computer systems
allow users to send messages to one another’s screens, browse
web pages, send electronic-mail messages, log in remotely,
transfer files from one machine to another
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Ch2. Operating-System Structures
OS Design and Implementation
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Ch2. Operating-System Structures
Operating System Design and Implementation
 Design and Implementation of OS is not “solvable”

but some approaches have proven successful
 Internal structure of different OS can vary widely
 Defining goals and specifications

Affected by choice of hardware, type of system
 batch, multiprogramming, multitasking
 single user, multi-user
 distributed, real-time, general purpose.
 User goals and System goals
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
User goals – operating system should be convenient to use, easy to learn,
reliable, safe, and fast
System goals – operating system should be easy to design, implement,
and maintain, as well as flexible, reliable, error-free, and efficient
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Ch2. Operating-System Structures
Operating System Design and Implementation
 Important principle to separate
Policy: What will be done?
Mechanism: How to do it?
 Mechanisms determine how to do something.
 Policies decide what will be done.
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
The separation of policy from mechanism is a very important
principle,
it allows maximum flexibility if policy decisions are to be changed
later
 Once an operating system is designed, it must be
implemented


Traditionally, written in assembly language.
Now, written in high-level languages (C: Linux and Windows)
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Ch2. Operating-System Structures
Operating System Structure
1.
2.
3.
4.
Simple Structure
Layered Structure
Microkernel System Structure
Modular Kernel Structure - Modern OS
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Ch2. Operating-System Structures
1. Simple Structure
 MS-DOS
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Policy - to provide the most functionality in the least space

Not divided into modules

Although MS-DOS has some structure, its interfaces and levels of
functionality are not well separated
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Ch2. Operating-System Structures
MS-DOS Layer Structure
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Ch2. Operating-System Structures
2. Layered Approach
 The operating system is divided into a number of layers
(levels), each built on top of lower layers.
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
The bottom layer (layer 0), is the hardware;
The highest (layer N) is the user interface.
 With modularity, layers are selected such that each uses
functions (operations) and services of only lower-level
layers


A typical OS layer (layer M) consists of data structure and a set of
routines that can be invoked by higher-level layers.
Layer M, in tern, can invoke operations on lower-level layers.
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Ch2. Operating-System Structures
Layered Operating System
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Ch2. Operating-System Structures
Layered Approach
 Advantage




Simplicity of construction and debugging
The design and implementation is simplified.
Each layer is implemented with only those operations provided by
lower-level layers.
A layer does not need to know how these operations are
implemented.
 Disadvantage


Appropriately defining the various layers
Because a layer can use only lower-level layers, careful planning is
necessary.
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Ch2. Operating-System Structures
UNIX
 The UNIX OS consists of two separable parts


Systems programs
The kernel
 Consists of everything below the system-call interface and
above the physical hardware

Provides the file system, CPU scheduling, memory
management, and other operating-system functions; a large
number of functions for one level
 As UNIX expanded, the kernel became large.
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Ch2. Operating-System Structures
UNIX System Structure
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Ch2. Operating-System Structures
3. Microkernel System Structure
 Make the kernel as light as possible.



moves as much from the kernel into “user” space
Communication takes place between user modules using message
passing
Mach OS from Carnegie Mellon Univ.
 Advantage



Easier to extend a microkernel
Easier to port the operating system to new architectures
More reliable (less code is running in kernel mode) and secure
 Disadvantage

Performance overhead of user space to kernel space
communication
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Ch2. Operating-System Structures
4. Modular Kernel Structure
 Most modern operating systems implement kernel
modules
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
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The kernel has a set of core components and dynamically links to
additional services either during boot time or during run time.
uses object-oriented approach
Each core component is separate
Each talks to the others over known interfaces
Each is loadable as needed within the kernel
 Overall, similar to layers but with more flexible
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Ch2. Operating-System Structures
Solaris Modular Approach
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Ch2. Operating-System Structures
Modular Kernel Structure
 The Modular kernel approach is similar to the Layered
approach

The modular kernel approach requires subsystems to interact with
each other through carefully constructed interfaces
 However, the Modular kernel approach differs from the
Layered approach


The layered kernel imposes a strict ordering of subsystems such
that subsystems at the lower layers are not allowed to invoke
operations corresponding to the upper-layer subsystems.
There are no such restrictions in the modular-kernel approach,
wherein modules are free to invoke each other without any
constraints.
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Ch2. Operating-System Structures
Virtual Machine
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Ch2. Operating-System Structures
Virtual Machines
 A virtual machine takes the layered approach to its logical
conclusion.
 It treats hardware and the operating system kernel as
though they were all hardware
 A virtual machine provides an interface identical to the
underlying bare hardware
 The operating system creates the illusion of multiple
processes, each executing on its own processor with its
own (virtual) memory
 The resources of the physical computer are shared among
the virtual machines
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Ch2. Operating-System Structures
Virtual Machines
Non-virtual Machine
Virtual Machine
(a) Nonvirtual machine
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(b) virtual machine
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Ch2. Operating-System Structures
Virtual Machines
 The virtual-machine concept provides complete protection
of system resources since each virtual machine is isolated
from all other virtual machines. This isolation, however,
permits no direct sharing of resources.
 A virtual-machine system is a perfect vehicle for operatingsystems research and development. System development
is done on the virtual machine, instead of on a physical
machine and so does not disrupt normal system operation.
 The virtual machine concept is difficult to implement due to
the effort required to provide an exact duplicate to the
underlying machine
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Ch2. Operating-System Structures
VMware Architecture
http://www.vmware.com/
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Ch2. Operating-System Structures
The Java Virtual Machine
http://java.sun.com/
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Ch2. Operating-System Structures
Summary
 OS provides a number of services


Functions that are helpful to the user
 user interface, program execution, I/O operation
 file system manipulation, communications, error detection
Functions that ensure the efficient operation of the system
 resource allocation , accounting, protection and security
 Three types of user interface from OS

CLI, GUI, Batch Interface
 System calls allow a process to make requests to the OS.

To send a request, program use system APIs or standard library functions which
are translated into a sequence of system calls.
 Three methods of parameter passing in system call

Register, Block, Stack
 The separation of policy from mechanism is a very important principle in the
design of OS
 Four types of OS structures

Simple, Layered, Microkernel, Modular
 Virtual machine is an illusion of a computer system with own CPU, memory
and I/O, which is created on top of host OS.
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Silberschatz, Galvin and Gagne ©2006
Operating System Principles
End of Chapter 2
Mi Jung Choi
[email protected]
Dept. of Computer Science