[SOLVED] CS CS162 Operating Systems and Systems Programming

CS162 Operating Systems and Systems Programming
June 21, 2022 Rahul & Edward cs162.org

Introduction

Copyright By Assignmentchef assignmentchef

A Simple Computer
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This system is not easy to use! Why?
Not set up to run multiple programs at the same time
What if you run a program with an infinite loop
Programs have to know how to talk to all kinds of hardware
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Task Manager
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Introduction
There is a body of software that is responsible for making it easy to run programs
This body of software is the Operating System.
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What does an Operating System do?
Share CPU across multiple running programs
Isolate different running programs
Create the notion of files and directories
Provide special services to running programs
Abstract hardware details away from running programs
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Lines of Code
Millions of Lines of Code
(source https://informationisbeautiful.net/visualizations/million-lines-of-code/)
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Course Info & Logistics

Why take CS162?
Some of you will actually design and build operating systems.
Many of you will create systems that utilize the core concepts in operating systems.
The concepts and design patterns appear at many levels
All of you will build applications that utilize operating systems.
The better you understand their design and implementation, the better use youll make of them.
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Who am I? Edward
Graduating senior
CS & Math
6th time on CS162 staff
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Who am I? Rahul
Graduating senior
2nd time on CS162 staff
Previously:EE105,EE140,CS189
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CS162 TAs and Readers
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Course Format
Discussion
In-person, with recorded walkthroughs, 2 sections a week
Office Hours
Project Party
Operating Systems: Principles and Practice (2nd Edition) by Anderson and
cs162.org, all course info can be found here. Piazza for questions.
6 homework assignments (HW0, PROJ0, HW1, HW2, HW3, HW4)
3 group projects (PROJ1, PROJ2, PROJ3)
1 midterm exam
1 final exam
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Getting started
Everyone
Start homework 0 right away
Attend any section you want
Find group members if you havent already
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Assignments
Individual Homeworks
HW0.Tools & Environment,Autograding, recall C, executable PROJ0. Getting Started with PintOS
HW1. Lists in C
HW2. BYOS build your own shell
HW3. Sockets & Threads in HTTP server
HW4. Memory management and MALLOC
Three Group Projects
PROJ1. User-programs (exec & syscall)
PROJ2.Threads & Scheduling (no user multi-threading) PROJ3. File Systems
Extensions policy and form on course website
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Group Projects
Project teams have 4 members!
Each project team will be assigned a TA.
Communication and cooperation will be essential
Joint work on Design Documents
Slack/Messenger/whatever doesnt replace face-to-face!
Everyone should do work and have clear responsibilities
You will evaluate your teammates at the end of each project Not all tasks are equal.Work as a team.
Communicate with your TA
What is the teams plan?
What is each members responsibility?
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PreparingYourself for this Class
The projects will require you to be very comfortable with programming and debugging C
Pointers (including function pointers, void*)
Memory Management (malloc, free, stack vs heap) Debugging with GDB
You will be working on a larger, more sophisticated code base than anything youve likely seen in 61C!
Review Session on C on 6/24
Resources page on website Ebooks on git and C
C programming reference (still in beta): https://cs162.eecs.berkeley.edu/ladder/
First section is dedicated to programming and debugging review
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40% exams
40% projects
20% homework
Projects
Initial design document, design review, code, final report
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CS 162 Collaboration Policy
Explaining a concept to someone in another group Discussing algorithms/testing strategies with other groups Discussing debugging approaches with other groups Searching online for generic algorithms (e.g. hash table)
Sharing code or test cases with another group
Copying OR reading another groups code or test cases Copying OR reading online code or test cases from prior years Helping someone in another group to debug their code
We have tools to detect academic misconduct and will take actions against offenders.
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Basic OS Concepts
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Basic OS Concepts
Operating systems abstract away the underlying hardware
They provide an easier-to-use interface for user programs
Well see several examples in the next few slides
This is just an overview; well go into much more detail later on
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Processes and Threads
Hardware: CPU
OS abstraction: processes and threads
Whats in a process?
Address Space
One or more threads of control executing in that address space
Additional system state associated with it Open files
Open sockets (network connections)
Application
Operating System
Abstract Machine Interface Physical Machine Interface
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Hardware Multiplexing
What if you want to run 2 processes on 1 single-core CPU?
Give the illusion that both are running simultaneously
Applications cant be trusted to voluntarily give up the CPU
OS needs a mechanism to retake control of the CPU
Typically: a hardware timer interrupts the CPU, giving control to the OS The OS can then pick another thread/process to run
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Filesystems
Hardware: Disk
OS abstraction: files/directories
How does the OS provide a filesystem?
Disk is essentially just a collection of bytes, organized into chunks called sectors
Ask disk to load ith sector; get back a chunk of (say) 4096 bytes
When you access the file /a/b/c/foo.txt, OS translates the file path into a set of sectors that store the contents of foo.txt
Applications dont worry about how exactly the disk works; they can think solely in terms of files and directories
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Hardware: Physical memory (usually SRAM/DRAM) OS abstraction:Virtual memory
Like disk, physical memory is just a collection of chunks of bits
OS performs address translation: converting virtual addresses into physical addresses to send to the memory controller
Applications can act as if they have their entire address space to themselves
Address translation often accelerated by hardware
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Isolation/Security
Isolation is a very important job of the operating system!
Processes should not be able to access memory belonging to another process
Bugs in one application should not crash the entire system
Applications must not be able to read or modify operating system data
Other security features the OS helps enforce:
Filesystem permissions (read/write/execute, access control lists)
Firmware verification / secure boot
Firewalls / network access control
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Only one way for applications to use OS services: syscalls.
Syscalls are the interface between user programs and the OS kernel
The narrow waist between user programs and the kernel
Use syscalls to:
open/read/write files
create processes
access the network
get the system time
communicate with other processes
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Example: Shell
Before modern user interfaces, the shell was the only way to interact with a computer.
Nowadays, shells are wrapped in their own graphical user interface. Many flavors:sh,bash,fish,zsh,csh
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What happens when you run ls? 1. Shell reads the command, and parses arguments.
Command:ls /
Two arguments:ls, /
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What happens when you run ls? 2. Shell searches for an executable file called ls.
Where does it search? The directories listed in PATH. How can you tell which file it found? Run which ls.
On my system:/bin/ls.
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What happens when you run ls?
3. Shell spawns a new process running the executable /bin/ls.
Syscalls:fork, exec.
Shell passes the arguments [ls, /] to this process.
Fork returns a PID (process ID) well use this later!
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What happens when you run ls? 4.The process running ls reads the current working directory.
Syscalls:opendir, readdir,
How does it know which directory to read? The current working directory is inherited by the child process.
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What happens when you run ls? 5. ls writes the directory entries to its standard output.
Syscalls: write.
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What happens when you run ls? 6.The shell displays the standard output.
Child processes inherit standard output.
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What happens when you run ls?
7.The shell waits for ls to finish before prompting you for another command.
Syscalls:wait, waitpid.
Repeat the same process for other commands! A bit more complicated: shells
support redirection, pipes, aliases, etc.
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PintOS is the educational operating system we use in all projects.
Youll add several basic features:
Project 1: User program support Argument passing
Syscalls
Project 2: Scheduling
Scheduling
Timer interrupts
Thread synchronization
Project 3: Filesystems Files
Directories Cache
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In conclusionOperating Systems:
Provide convenient abstractions to handle diverse hardware
Convenience, protection, reliability obtained in creating the illusion
Coordinate resources and protect users from each other Using a few critical hardware mechanisms
Simplify application development by providing standard services Provide fault containment, fault tolerance, and fault recovery
CS162 combines things from many other areas of computer science: Languages, data structures, hardware, and algorithms
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Acknowledgements
Slides courtesy of, . Joseph,,AJ Shankar,,AlexAiken, , ,Ion Stoica,DougTygar, ,,
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CS: assignmentchef QQ: 1823890830 Email: [email protected]