A PAPER PRESENTATION ON

SOFTWARE ARCHITECTURE OF LINUX

WHAT IS INSIDE

1 Introduction

2 Need of the study of Software Architecture

3 System Structure4 Subsystem Inspection5 Future Work6 References

INTRODUCTION

Linus B. Trovalds wrote the Linux Kernel in 1991.

Free and Open SourceA Unix compatible systemOriginally developed to run on the Intel

80386

Need for the Software Architecture StudyEnhance communication among stakeholders

of the systemSupport for earlier design decisions.Understand transferable abstraction of a

systemSoftware maintenanceExploit the FOSS utilities. To extend, remove,

change,modify functionality of an existing system.

Linux System Structure

Criticism-“Linux kernel is useless by itself,it participates as one layer in the overall system.”

Within the kernel layer Linux has 5 major subsystems.

Process SchedulerMemory ManagerVirtual File SystemNetwork interfaceInter process communication

Sub System InspectionProcess Scheduler

Sub System Inspection - Process SchedulerIt is the heart of Linux Operating SystemFunctions: Allows processes to make new copies.SchedulingInterrupt HandlingLoading, Executing and Terminating of

processes.Timer ManagementSupport for Dynamically loaded modules.

Process Scheduler Dependencies

Sub System Inspection –Memory ManagerProvides:Large address spaceProtectionMemory mappingFair access to Physical memoryShared MemoryMemory Manager abstracts details of all hardware

platforms into one common interface. It maps virtual addresses to physical memory addresses.

It also swaps out processes to allow system to execute processes that use more physical memory than available on the system.

Daemon threads

Memory Manager Dependencies

Subsystem Inspection: Virtual File SystemLinux supports:Multiple hardware devicesMultiple logical File SystemMultiple Executable FormatsHomogenity PerformanceSafetySecurity

The FS of Linux has 2 conceptual layers 1. Device Driver Layer

2. Virtual File systemAdd new Device Driver by simply implementing the

abstract interface,Use of Buffer Cache for optimized Performance.Data Transfer can takes place by1.Polling 2.DMA 3.InterruptsTo support Virtual FS Linux has inodes.It makes all

files appear the same to other Linux subsystems

Subsystem Inspection: Virtual File System

VFS Dependencies

Subsystem Inspection:Inter Process Communication

Concurrent Execution of processes for

*Resource Sharing

*Synchronization

*Exchange of dataLinux provides following forms of IPC

-Signals

-Wait Queues

-File Locks

-Pipes and Named PipesSystem VIPC:

->Semaphore ->Message Queues ->Shared Memory

Interprocess Communication Dependencies

Linux supports network connections between machines and socket communication model.2 types of sockets are identified

-BSD sockets -INET sockets BSD abstracts the communication details to a

common interface. This provides greater portability Linux provides two transfer layer protocols

UDP TCP

INET sits on top of both IP and Transport Protocol.

Subsystem Inspection-Network Interface

Subsystem Inspection-Network InterfaceThree types of connections-Serial Line connections-Parallel Line connections-Ethernet connectionsAn address Resolver (ARP)is responsible for

converting the IP addresses into physical ones. This is necessary as sockets deal with IP addresses which cannot be directly used by hardware devices.

Subsystem Inspection-Network Interface

ConclusionLinux has since been ported to more computer hardware

platforms than any other operating system. It is a leading operating system on servers and other big iron

systems such as mainframe computers and supercomputers more than 90% of today's 500 fastest supercomputers run some variant of Linux .

Linux also runs on embedded systems such as mobile phones, tablet computers, network routers, televisions and video game consoles the Android system in wide use on mobile devices is built on the Linux kernel.

Typically Linux is packaged in a format known as a Linux distribution for desktop and server use. Some popular mainstream Linux distributions include Debian , Fedora and openSUSE.

Future WorkConceptual Architecture shows few dependencies among the components than concrete architectureThe PBS tools should be adjusted to handle the Linux source structure. The conceptual and concrete architectures we have presented should be refined through discussions with the Linux developer community. After refinement, the two models can be compared using the Reflexion model [Murphy 1995].

References[Balasubramanian 1993]

Balasubramanian, K. and Johnson D.: "Linux Memory Management Overview," The Linux Kernel Hacker’s Guide,

http://www.redhat.com:8080/hypernews/get/memory/memory.html

[Tanuan 1998]

Tanuan,M.: "An Introduction to the Linux Operating System Architecture", http://www.grad.math.uwaterloo.ca/~mcta

Sahun Siddiqi,Meyer Tanaun,Ivan Bowman:

“Concrete Architecture of Linux”

LINUX- powerful. open source. secure