1 Last class: Computer architecture support for systems Today: - - PowerPoint PPT Presentation

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1 Last class: Computer architecture support for systems Today: - - PowerPoint PPT Presentation

Jan 05, 2023 286 likes •548 views

1 Last class: Computer architecture support for systems Today: Operating Systems Structures and Basics 2 Interlude Recap of OS goals Resource management Memory, Devices Scheduling Security Services to

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  • Last class:

– Computer architecture support for systems

  • Today:

– Operating Systems Structures and Basics

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Interlude

  • Recap of OS goals

– Resource management

  • Memory, Devices

– Scheduling – Security – Services to programs/applications

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Functionality Expected from a Modern OS

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Libertarian View

  • Everyone should get to do

whatever they want

– As long as they let others live

  • Processes should feel they have

the entire computer

– Infinite CPU, RAM, … – No threat of someone harming them

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Socialistic View

  • To each according to

his needs

– Co-operative existence enforced by govt/OS – Fair allocation of resources

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OS as a Communist Govt.

  • Centralized control

and monitoring

  • Allocate resources

efficiently

  • Misbehavior =>

Termination

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Theory vs. Practice

  • The Theory

– Many OS problems are NP-complete

  • What’s the best schedule for all possible processes?

– So, optimal solutions are not possible

  • What do we do?
  • Evaluate (preferably, using appropriate

workload)

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Software Architecture

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Operating System Layers

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System Layers

  • Application
  • Libraries (in application process)
  • System Services
  • OS API
  • Operating system kernel
  • Hardware

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  • Application Programming Interface

– Library functions (e.g., libc)

  • Examples

– printf of stdio.h

  • All within the process’s address space

– Static and Dynamic linking

Applications to Libraries

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Applications to Services

  • Provide syntactic sugar for using resources

– Printing, program mgmt, network mgmt, file mgmt, etc. – E.g., chmod

  • Provide special functions beyond OS

– E.g., cron

  • UNIX man pages, sections 1 and 8

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Libraries to System

  • System call interface

– UNIX man pages, section 2 – Examples

  • open, read, write – defined in unistd.h

– Call these via libraries? fopen vs. open

  • Special files

– Drivers, /proc, sysfs

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System to Hardware

  • Software-hardware interface
  • OS kernel functions

– Concepts == Managers -- Hardware – Files == drivers -- devices – Address space == virtual memory -- memory – Instruction Set == process model -- CPU

  • OS provides abstractions of devices and hardware
  • bjects (files)

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System Call Overview

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System Call Handling

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System Call Handling

  • Procedure call in user process
  • Initial work in user mode

(libc)

  • Trap instruction to invoke kernel

(int 0x80)

  • Preparation

(e.g., sys_read, mmap2)

  • I/O command

(read from disk)

  • Wait

(disk is slow)

  • Completion

(interrupt handling)

  • Return-from-interrupt instruction
  • Final work in user mode

(libc)

  • Ordinary return instruction

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File Interface

  • Goal: Provide a uniform abstraction

for accessing the OS and its resources

  • Abstraction: File

– Use file system calls to access OS services – Devices, sockets, pipes, etc. – And OS in general

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Regular File

  • File has a pathname: /tmp/foo
  • Can open the file

– int fd = open( “/tmp/foo”, O_RDWR ) – For reading and writing

  • Can read from and write to the file

– bytes = read( fd, buf, max ); /* buf get output */ – bytes = write( fd, buf, len ); /* buf has input */

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Socket File

  • File has a pathname: /tmp/bar

– Files provide a persistence for a communication channel – Usually used for local communication (UNIX domain sockets)

  • Open, read, and write via socket operations

– sockfd = socket( AF_UNIX, TCP_STREAM, 0 ); – local.path is set to /tmp/bar – bind ( sockfd, &local, len ) – Use sock operations to read and write

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Device File

  • Files for interacting with physical devices

– /dev/null (do nothing) – /dev/cdrom (CD-drive)

  • Use file system operations, but are handled in

device-specific ways

– Open, read, write correspond to device-specific functions

  • Function pointers!

– Also, use ioctl (I/O control) to interact (later)

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Sysfs File and /proc Files

  • These files enable reading from and writing

to kernel

  • /proc files

– enable reading of kernel state for a process

  • Sysfs files

– Provide functions that update kernel data

  • File’s write function updates kernel based on input

data

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Summary

  • Operating systems must balance many needs

– Impression that each process has individual use of system – Comprehensive management of system resources

  • Operating system structures try to make use of

system resources straightforward

– Libraries – System services – System calls and other interfaces

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  • Next time: Processes

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