Operating System Services and System Calls: An Overview, Slides of Operating Systems

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Lecture 3

Chapter 2: Operating-System Structures

Chapter 2: Operating-System Structures

• 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
• Operating System Debugging
• Operating System Generation
• System Boot

Operating System Services

• One set of operating-system services provides functions that are helpful to the user:
  • User interface - Almost all operating systems have a user

interface (UI)

• Varies between Command-Line (CLI), Graphics User Interface (GUI), Batch
• 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)

• 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. Programs need to read and write files and

directories, create and delete them, search them, list file

Information, permission management.

Operating System Services (Cont)

• One set of operating-system services provides functions that are helpful to the user (Cont): - 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 hardware, 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

User Operating System Interface - CLI

Command Line Interface (CLI) or command

interpreter allows direct command entry

• Sometimes implemented in kernel, sometimes by

systems program

• Sometimes multiple flavors implemented – shells
• Primarily fetches a command from user and executes

it

• Sometimes commands built-in, sometimes just names of programs

» If the latter, adding new features doesn’t require shell modification

User Operating System Interface - GUI

• User-friendly desktop metaphor interface
  • 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 (known as a folder)
  • Invented at Xerox PARC
• Many systems now include both CLI and GUI interfaces
  • Microsoft Windows is GUI with CLI “command” shell
  • Apple Mac OS X as “Aqua” GUI interface with UNIX kernel underneath and shells available
  • Solaris is CLI with optional GUI interfaces (Java Desktop, KDE)

The Mac OS X GUI

System Calls

• Programming interface to the services provided by the OS
• Typically written in a high-level language (C or C++)
• 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?

Example of Standard API

• Consider the ReadFile() function in the
• Win32 API—a function for reading from a file
• A description of the parameters passed to ReadFile()
  • HANDLE file the file to be read
  • LPVOID buffer a buffer where the data will be read into and written from
  • DWORD bytesToRead the number of bytes to be read into the buffer
  • LPDWORD bytesRead the number of bytes read during the last read
  • LPOVERLAPPED ovl indicates if overlapped I/O is being used

System Call Implementation

• Typically, a number associated with each

system call

– 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 need know nothing about how theDocsity.com

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

Types of System Calls

• Process control

• File management

• Device management

• Information maintenance

• Communications Docsity.com

Examples of Windows and Unix System Calls