Ch2 OS Services F24 (2).pptx

Chapter 2: Operating-System Services Operating System Concepts – 10th Edition Silberschatz, Galvin and Gagne ©2018  Outline  Operating System Services  User and Operating System-Interface  Sy...

Chapter 2: Operating-System Services Operating System Concepts – 10th Edition Silberschatz, Galvin and Gagne ©2018  Outline  Operating System Services  User and Operating System-Interface  System Calls  System Services  Linkers and Loaders Operating System Concepts – 10th Edition 2.2 Silberschatz, Galvin and Gagne ©2018  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).  Varieties: Command-Line (CLI), Graphics User Interface (GUI), Touch-screen, 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 Concepts – 10th Edition 2.3 Silberschatz, Galvin and Gagne ©2018  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 Operating System Concepts – 10th Edition 2.4 Silberschatz, Galvin and Gagne ©2018  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. Logging - 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 Operating System Concepts – 10th Edition 2.5 Silberschatz, Galvin and Gagne ©2018  A View of Operating System Services Operating System Concepts – 10th Edition 2.6 Silberschatz, Galvin and Gagne ©2018  Command Line interpreter  CLI 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 Operating System Concepts – 10th Edition 2.7 Silberschatz, Galvin and Gagne ©2018  Bourne Shell Command Interpreter Operating System Concepts – 10th Edition 2.8 Silberschatz, Galvin and Gagne ©2018  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 is “Aqua” GUI interface with UNIX kernel underneath and shells available Unix and Linux have CLI with optional GUI interfaces (CDE, KDE, GNOME) Operating System Concepts – 10th Edition 2.9 Silberschatz, Galvin and Gagne ©2018  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 Operating System Concepts – 10th Edition 2.10 Silberschatz, Galvin and Gagne ©2018  The Mac OS X GUI Operating System Concepts – 10th Edition 2.11 Silberschatz, Galvin and Gagne ©2018  System Calls  System calls provide Programming interface to the services made available by the OS  System calls are generally available as functions Typically written in a high-level language (C or C++) What if a task need lower-level access?  e.g., access a hardware such as secondary storage  Such system call is implemented in a lower-level language, i.e., Assembly Language Operating System Concepts – 10th Edition 2.12 Silberschatz, Galvin and Gagne ©2018  Example of System Calls  System call sequence that involves in a program to copy the contents of one file to another file  See *book for details description Operating System Concepts – 10th Edition 2.13 Silberschatz, Galvin and Gagne ©2018  API (Application Program Interface)  Frequently, systems execute thousands of system calls per second that programmers never see this level of detail  Typically, application developers design programs via a high-level API  The API specifies a set of functions that are available to an application programmer, including the parameters that are passed to each function and the return values the programmer can expect.  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), Java API for the Java virtual machine (JVM)  Behind the scenes, the functions that make up an API typically invoke the actual system calls on behalf of the application programmer. For example, the Windows API CreateProcess() actually invokes the NTCreateProcess() system call in the Windows kernel. Operating System Concepts – 10th Edition 2.14 Silberschatz, Galvin and Gagne ©2018  Example of Standard API Operating System Concepts – 10th Edition 2.15 Silberschatz, Galvin and Gagne ©2018  Benefits of using API 1. Program portability: An application programmer designing a program using an API can expect her program to compile and run on any system that supports the same API 2. Ease of programming: Actual system calls can often be more detailed and difficult to work with than the API available to an application programmer Operating System Concepts – 10th Edition 2.16 Silberschatz, Galvin and Gagne ©2018  System Call Implementation  Run-time environment (RTE) handles system calls by its full suite of software needed to execute applications written in a given programming language, including its compilers, interpreters, libraries and loaders.  Provides system-call Interface that is a link to system calls  Typically, a number is 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 Operating System Concepts – 10th Edition 2.17 Silberschatz, Galvin and Gagne ©2018  API – System Call – OS Relationship Operating System Concepts – 10th Edition 2.18 Silberschatz, Galvin and Gagne ©2018  Types of System Calls System calls can be grouped roughly into six major categories: i. Process control, ii. File management, iii. Device management, iv. Information maintenance, v. Communications, vi. Protection. Operating System Concepts – 10th Edition 2.21 Silberschatz, Galvin and Gagne ©2018  Types of System Calls (cont.) 1. 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 Operating System Concepts – 10th Edition 2.22 Silberschatz, Galvin and Gagne ©2018  Types of System Calls (Cont.) 2. File management create file, delete file open, close file read, write, reposition get and set file attributes 3. Device management request device, release device read, write, reposition get device attributes, set device attributes logically attach or detach devices Operating System Concepts – 10th Edition 2.23 Silberschatz, Galvin and Gagne ©2018  Types of System Calls (Cont.) 4. Information maintenance get time or date, set time or date get system data, set system data get and set process, file, or device attributes 5. 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 Operating System Concepts – 10th Edition 2.24 Silberschatz, Galvin and Gagne ©2018  Types of System Calls (Cont.) 6. Protection Control access to resources Get and set permissions Allow and deny user access Operating System Concepts – 10th Edition 2.25 Silberschatz, Galvin and Gagne ©2018  Examples of Windows and Unix System Calls Operating System Concepts – 10th Edition 2.26 Silberschatz, Galvin and Gagne ©2018  Standard C Library Example  C program invoking printf() library call, which calls write() system call Operating System Concepts – 10th Edition 2.27 Silberschatz, Galvin and Gagne ©2018  Example: FreeBSD  Unix variant  Multitasking  User login -> invoke user’s choice of shell  Shell executes fork() system call to create process Executes exec() to load program into process Shell waits for process to terminate or continues with user commands  Process exits with: code = 0 – no error code > 0 – error code Operating System Concepts – 10th Edition 2.28 Silberschatz, Galvin and Gagne ©2018  System Services  System programs provide a convenient environment for program development and execution. They can be divided into: File manipulation Status information sometimes stored in a file Programming language support Program loading and execution Communications Background services Application programs  Most users’ view of the operating system is defined by system programs, not the actual system calls Operating System Concepts – 10th Edition 2.29 Silberschatz, Galvin and Gagne ©2018  System Services (Cont.)  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 Operating System Concepts – 10th Edition 2.30 Silberschatz, Galvin and Gagne ©2018  System Services (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 Concepts – 10th Edition 2.31 Silberschatz, Galvin and Gagne ©2018  System Services (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 Run in user context not kernel context Known as services, subsystems, daemons  Application programs Don’t pertain to system Run by users Not typically considered part of OS Launched by command line, mouse click, finger poke Operating System Concepts – 10th Edition 2.32 Silberschatz, Galvin and Gagne ©2018  Linkers and Loaders  Source code compiled into object files designed to be loaded into any physical memory location – relocatable object file  Linker combines these into single binary executable file Also brings in libraries  Program resides on secondary storage as binary executable  Must be brought into memory by loader to be executed Relocation assigns final addresses to program parts and adjusts code and data in program to match those addresses  Modern general purpose systems don’t link libraries into executables Rather, dynamically linked libraries (in Windows, DLLs) are loaded as needed, shared by all that use the same version of that same library (loaded once)  Object, executable files have standard formats, so operating system knows how to load and start them Operating System Concepts – 10th Edition 2.33 Silberschatz, Galvin and Gagne ©2018  The Role of the Linker and Loader Operating System Concepts – 10th Edition 2.34 Silberschatz, Galvin and Gagne ©2018  Why Applications are Operating System Specific  Apps compiled on one system usually not executable on other operating systems  Each operating system provides its own unique system calls Own file formats, etc.  Apps can be multi-operating system Written in interpreted language like Python, Ruby, and interpreter available on multiple operating systems App written in language that includes a VM containing the running app (like Java) Use standard language (like C), compile separately on each operating system to run on each  Application Binary Interface (ABI) is architecture equivalent of API, defines how different components of binary code can interface for a given operating system on a given architecture, CPU, etc. Operating System Concepts – 10th Edition 2.35 Silberschatz, Galvin and Gagne ©2018  End of Chapter 2 Operating System Concepts – 10th Edition Silberschatz, Galvin and Gagne ©2018