Operating Systems - OS3 · • System Calls are the interface the Operating System offers to...

Operating Systems

Operating Systems - Winter 2012

Andrew S. TanenbaumMelanie Rieback

Arno Bakker

Design and Implementation

Vrije Universiteit Amsterdam

Outline

Vrije Universiteit Amsterdam Slide 4

• Introduction• What is an OS?

• Concepts

• Processes and Threads

• Memory Management

• File Systems

Operating Systems 2012

Chap 1 - Overview


• What is an Operating System?

• Concepts

• System Calls

• Structure


What is an OS?



2 Views on OSes


• OS as a Virtual Machine

• Extending the HW functionality

• Hides the messy details of programming the HW

• OS as a Resource Manager

• Protects against simultaneous usage of resources

• Fair sharing of resources (scheduling)

• Resource accounting


How to View an OSOperating Systems 2011


OS

Program

System calls

Concept: ProcessesOperating Systems 2011


Multiple ProcessesOperating Systems 2011


some_program

init

shell

System CallsOperating Systems 2011


Hardware

Operating SystemSystem Calls

LibrariesLibrary functions

Applications / Processes

Instruction Set Architecture

• System Calls are the interface the Operating System offers to applications.• Problem: Mechanics of issuing a system call are highly machine dependent• Solution: Provide a library to allow system calls from C programs: libc

Bashlibc

Linux kernel

x86_64

System Calls: Process Management (1/2)


System Calls: Process Management (2/2)


System Calls: SignalsOperating Systems 2011


Concept: Mounting (1/2) Operating Systems 2011


File System Mounting (2/2) Operating Systems 2011


Special Files (1/2) Operating Systems 2011


Storage devices are mapped into the file tree via mounting. Idea: do this for all devices.

Mechanism: Special files in /dev

Two types:

Special Files (2/2) Operating Systems 2011


System Calls: FilesOperating Systems 2011


System Calls: DirectoriesOperating Systems 2011


System Calls: Implementation Operating Systems 2011


OS Structure: UNIXOperating Systems 2011


OS Structure: LinuxOperating Systems 2011


Operating Systems


Chapter 2 - Processes


Chap 2 - OverviewOperating Systems 2012


• Scheduling Processes

• Threads

Recall: Process



One CPU, Many Processes



• Processes share the CPU(s)• A scheduler determines which process to run next• Keeps track of the process state• Following some scheduling policy (random robin, shortest

job first, etc).

Process States



Context SwitchingOperating Systems 2011


Process ImplementationOperating Systems 2011


ProcessTable: ps -ef

ThreadsOperating Systems 2011


Threads: Minimal SupportOperating Systems 2011


Threads – Some ProblemsOperating Systems 2011


Mutual ExclusionOperating Systems 2011


Operating Systems


Chapter 4 – Memory Management




• Memory Management

• Paged Memory

• Virtual Memory

• Segmentation

Memory Management – SimpleOperating Systems 2012


Memory Management - ComplexOperating Systems 2012


Multiple processes in the same memory

Paged Memory Systems (1/2) Operating Systems 2012


Paged Memory Systems (2/2)


Virtual Memory Operating Systems 2012


• Idea: Not all virtual pages have to be in physical memory• Instead stored on disk -> cheap storage• In swap partition• Much more memory available• Works if not all pages are used at the same time

Segmentation Operating Systems 2012


Stack

Data

Code

N

0Code Data Stack

N

0

• Segments can grow independently• Hardware helps to map segments to virtual memory• Hardware helps to protect: read-only, no-execute

Operating Systems


Chapter 5 – File Systems




• Files

• Directories

• File system implementation

• UNIX/MINIX filesystem

Directories



i-node

File Attributes



Directories – Pathnames



File System Design



File Storage: Disk Layout



File Storage – Inodes



File Storage – UNIX



File Storage – Name Resolution



Disk Space Management (1/2)



File System Consistency



Buffer Cache



Log-Structured File Systems



MINIX Filesystem



MINIX Superblock



Operating Systems - OS3 · • System Calls are the interface the Operating System offers to...

Documents

Transcript of Operating Systems - OS3 · • System Calls are the interface the Operating System offers to...