2.1 Silberschatz, Galvin and Gagne ©2009Operating System Concepts with Java – 8 th Edition Chapter 2: Operating-System Structures

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

Chapter 2: Operating-System Structures


Standard C Library Example

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


System Call Parameter Passing

Often, more information is required than simply identity of desired system call Exact type and amount of information vary according to OS and

call

Three general methods used to pass parameters to the OS 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


Parameter Passing via Table


Types of System Calls

Process control

File management

Device management

Information maintenance

Communications

Protection


Examples of Windows and Unix System Calls


Process Control Issues

Loading and executing a programWhat happens to the existing program?

LostSuspended (saved and allowed to

continue later)Run concurrently (needs creation of new

process) Control execution of the new program (set

priority, set max execution time, terminate)


Process Control Issues (Contd.)

Waiting for jobs

wait time, wait event and signal event

Managing shared data

acquire lock, release lock, etc.

Handling termination process (Normal or abnormal)

Taking memory dump

Return control to calling process


MS-DOS execution

(a) At system startup (b) running a program


FreeBSD Running Multiple Programs


File Management Issues

Creating files and directories

Deleting files and directories

Read and write

Reposition

Set attributes and get attributes

Move and copy

Some OSes provide explicit system calls

Others provide API which is implemented using other system calls


Device Management Issues

Physical and virtual resources

Request and release devices in multi-user OS

Needed to ensure exclusive access to devices

Unmanaged access can lead to device contention and deadlocks

Read, write, reposition

Unix treats devices as files


Information Management Issues

Transferring information between OS and user programs

System time, date, information about users, processes, resources etc.

Tracing and debugging programs

Dumping, trace, etc.

Single step

Profiling of programs

Get and set of attributes of processes


Communication Issues

Message passing model

exchange between processes on same machine or different machine

Needs opening of a connection

Host name and process id

Open, close, accept connections

Daemon processes – waiting on incoming connections


Shared Memory

Shared memory create

Shared memory attach

Process inform OS that they want to remove the OS placed restriction about accessing each others memory

Modalities of data sharing determined by the processes and not the OS


System Programs

System programs provide a convenient environment for program development and execution. The can be divided into:

File manipulation

Status information

File modification

Programming language support

Program loading and execution

Communications

Application programs

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


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

File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories

Status information

Some ask the system for info - date, time, amount of available memory, disk space, number of users

Others provide detailed performance, logging, and debugging information

Typically, these programs format and print the output to the terminal or other output devices

Some systems implement a registry - used to store and retrieve configuration information


System Programs (Cont.)

File modification 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 Program loading and execution- Absolute loaders, relocatable loaders,

linkage editors, and overlay-loaders, debugging systems for higher-level and machine language

Communications - 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


Operating System Design and Implementation

Design and Implementation of OS not “solvable”, but some approaches have proven successful

Internal structure of different Operating Systems can vary widely

Start by defining goals and specifications

User goals and System goals User goals - Should be convenient to use, easy to learn,

reliable, safe, and fast

System goals - Should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

Affected by choice of hardware, type of system


Mechanism – Policy Separation

Policy: What will be done? Mechanism: How to do it? Examples

Class attendance credit – card scanner/signup sheet/roll call

Time-multiplexing of CPU – Timer constructLRU – Linked list implementation

The separation of policy from allows maximum flexibility if policy decisions are to be changed laterSolaris Scheduler


OS Implementation

Early OSes were written in assembly language Currently most OSes are written in C Advantages of using high-level language

Faster, compactEasier to understand, debug and take advantage of

compiler optimizationsPortable – MS DOS Vs. Unix

Possible disadvantage?Performance


OS Structure

Describes how the code of the OS is organized

Function call, information flow, etc.

Not enough thought on structure in early OSes

Heavy price - crashes, vulnerabilities, etc.

MS-DOS – written 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


MS-DOS Layer Structure


OS Structures (Contd.)

Monolithic Kernel

Layered Structure

Micro-Kernel

Modular Approach


Monolithic Kernel

Approach followed by early UNIX

Kernel and system programs

Kernel is a collection of various sub-systems

File system

CPU Scheduling

Memory management

Communications

Very hard to maintain

Especially modifying or adding new functionality


Traditional UNIX System Structure


Layered Approach OS built as a set of layers

Bottom most layer is hardwareTop most layer is user interface

Each layer can invoke functionalities from layer immediately below it

AdvantagesEasy debugging Information hidingCode modifications are relatively simple

DrawbacksPlacing routines in layersLess efficient – too many calls across layers and too

much data passing


Layered Operating System


Microkernel System Structure

Mach OS by CMU to address problems with monolithic kernel

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

Detriments: Performance overhead of user space to kernel space communication


Modules

Modern OSes implement kernel modulesUses object-oriented approach

Each core component is separate

Each talks to the others over known interfaces

Each is loadable as needed within the kernel

Features can be implemented dynamically

Overall, similar to layers but with more flexibility


Solaris Modular Approach


Hybrid Structure of Mac OS X


Virtual Machines

VM technology takes layered approach to its logical conclusion

Pioneered by IBM CP/CMS in 1967 Abstracts hardware resources into several

different executing environmentEach environment will be a separate machine

A VM provides an interface identical to the underlying bare hardware

Guest process is an OS The operating system creates the illusion that it

has its own processor and (virtual memory).


Virtual Machines (Cont.)

(a) Nonvirtual machine (b) virtual machine


Virtual Machines Benefits

Physical machine protected from VMs and VMs protected from one anotherVirus in a guest OS will not affect the host OS

VMS can share files (through file system volume)

VMs can also communicate (via virtual network interfaces)

Aids in development and testing of OSEliminates system development time

Cloud computing and economies of scaleResource optimization through consolidation


Virtual Machines Implementation

Difficult to produce exact duplicate of the underlying machine

VM software can run in kernel mode. The VMs should execute only in user mode

Guest OSes also have user and kernel modes Virtual user mode – virtual kernel mode

transitionsSystem calls cause transfer to VM monitorVM monitor changes the register contents

and program counter and transfer control back to guest OS

VMs can be slow VMs need some level of hardware support


Operating-System Debugging

Debugging is finding and fixing errors, or bugs.

OSes generate log files containing error information.

Failure of an application can generate core dump file capturing memory of the process.

Operating system failure can generate crash dump file containing kernel memory.

Beyond crashes, performance tuning can optimize system performance.

Kernighan’s Law: “Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.”

DTrace tool in Solaris, FreeBSD, Mac OS X allows live instrumentation on production systems.

Probes fire when code is executed, capturing state data and sending it to consumers of those probes.


End of Chapter 2

Documents

2.1 Silberschatz, Galvin and Gagne ©2009Operating System Concepts with Java – 8 th Edition Chapter 2: Operating-System Structures