CSC 326 Chapter 2, Spring 2016

Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Chapter 2: Operating-System Structures 2.2 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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 2.3 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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  To explain how operating systems are installed and customized and how they boot 2.4 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Operating System Services  Operating systems provide an environment for execution of programs and services to programs and users  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 2.5 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Operating System Services (Cont.)  One set of operating-system services provides functions that are helpful to the user (Cont.):  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.  Communications – Processes may exchange information, on the same computer or between computers over a network  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 2.6 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Operating System Services (Cont.)  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 - CPU cycles, main memory, file storage, I/O devices.  Accounting - To keep track of which users use how much and what kinds of computer resources  Protection and security - The owners of information stored in a multiuser or networked computer system 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 2.7 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition A View of Operating System Services 2.8 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition User Operating System Interface - CLI 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 2.9 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Bourne Shell Command Interpreter 2.10 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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)  Many systems now include both CLI and GUI interfaces  Microsoft Windows is GUI with CLI “command” shell  Apple Mac OS X is “Aqua” GUI interface with UNIX kernel underneath and shells available  Unix and Linux have CLI with optional GUI interfaces (KDE, GNOME) 2.11 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Touchscreen Interfaces  Touchscreen devices require new interfaces  Mouse not possible or not desired  Actions and selection based on gestures  Virtual keyboard for text entry  Voice commands. 2.12 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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 Programming 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) Note that the system-call names used throughout this text are generic 2.13 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Example of System Calls  System call sequence to copy the contents of one file to another file 2.14 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Example of Standard API 2.15 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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 the intended system call in OS kernel and returns status of the system call and any return values  The caller need know nothing about how the system call is implemented  Just needs to obey API and understand what OS will do as a result call  Most details of OS interface hidden from programmer by API  Managed by run-time support library (set of functions built into libraries included with compiler) 2.16 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition API – System Call – OS Relationship 2.17 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Types of System Calls  Process control  create process, terminate process  end, abort  load, execute  get process attributes, set process attributes  wait for time  wait event, signal event  allocate and free memory  Dump memory if error  Debugger for determining bugs, single step execution  Locks for managing access to shared data between processes 2.18 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Types of System Calls  File management  create file, delete file  open, close file  read, write, reposition  get and set file attributes  Device management  request device, release device  read, write, reposition  get device attributes, set device attributes  logically attach or detach devices 2.19 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Types of System Calls (Cont.)  Information maintenance  get time or date, set time or date  get system data, set system data  get and set process, file, or device attributes  Communications  create, delete communication connection  send, receive messages if message passing model to host name or process name  From client to server  Shared-memory model create and gain access to memory regions  transfer status information  attach and detach remote devices 2.20 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Types of System Calls (Cont.)  Protection  Control access to resources  Get and set permissions  Allow and deny user access 2.21 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Examples of Windows and Unix System Calls 2.22 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Standard C Library Example  C program invoking printf() library call, which calls write() system call 2.23 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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  Most users’ view of the operation system is defined by system programs, not the actual system calls  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 2.24 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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 2.25 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition System Programs (Cont.)  Background Services  Launch at boot time  Some for system startup, then terminate  Some from system boot to shutdown  Provide facilities like disk checking, process scheduling, error logging, printing  Known as services, subsystems  Application programs  Don’t pertain to system  Run by users  Not typically considered part of OS  Launched by command line, mouse click, finger poke 2.26 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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 the design by defining goals and specifications  Affected by choice of hardware, type of system  User goals and System goals  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 2.27 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Implementation  Much variation  Early OSes in assembly language  Then system programming languages like Algol, PL/1  Now C, C++  Actually usually a mix of languages  Lowest levels in assembly  Main body in C  Systems programs in C, C++, scripting languages like PERL, Python, shell scripts  More high-level language easier to port to other hardware  But slower  Emulation can allow an OS to run on non-native hardware 2.28 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Operating System Structure  General-purpose OS is very large program  Various ways to structure ones  Simple structure – MS-DOS  More complex -- UNIX  Layered – an abstrcation  Microkernel -Mach 2.29 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Simple Structure -- MS-DOS  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 2.30 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Non Simple Structure -- UNIX UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. 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 2.31 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Traditional UNIX System Structure Beyond simple but not fully layered 2.32 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 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.  With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers 2.33 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Microkernel System Structure  Moves as much from the kernel into user space  Mach example of microkernel  Mac OS X kernel (Darwin) partly based on Mach  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)  Detriments:  Performance overhead of user space to kernel space communication 2.34 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Microkernel System Structure 2.35 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Modules  Many modern operating systems implement loadable kernel modules  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  Linux, Solaris, etc 2.36 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Solaris Modular Approach 2.37 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Hybrid Systems  Most modern operating systems are actually not one pure model  Hybrid combines multiple approaches to address performance, security, usability needs 2.38 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition iOS  Apple mobile OS for iPhone, iPad  Structured on Mac OS X, added functionality  Does not run OS X applications natively  Also runs on different CPU architecture (ARM vs. Intel)  Cocoa Touch Objective-C API for developing apps  Media services layer for graphics, audio, video  Core services provides cloud computing, databases  Core operating system, based on Mac OS X kernel 2.39 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Android  Developed by Open Handset Alliance (mostly Google)  Open Source  Similar stack to IOS  Based on Linux kernel but modified  Provides process, memory, device-driver management  Adds power management  Runtime environment includes core set of libraries and Dalvik virtual machine  Apps developed in Java plus Android API  Java class files compiled to Java bytecode then translated to executable than runs in Dalvik VM  Libraries include frameworks for web browser (webkit), database (SQLite), multimedia 2.40 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition Android Architecture Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition End of Chapter 2