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Презентация на тему Chapter 3process description and control

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RoadmapHow are processes represented and controlled by the OS. Process states which characterize the behaviour of processes. Data structures used to manage processes. Ways in which the OS uses these data structures to control process execution.
Chapter 3 Process Description and ControlOperating Systems: Internals and Design Principles, 6/E RoadmapHow are processes represented and controlled by the OS. Process states which Requirements of an Operating SystemFundamental Task: Process ManagementThe Operating System mustInterleave the ConceptsFrom earlier chapters we saw:Computer platforms consists of a collection of hardware Concepts cont…OS provides an interface for applications to useOS provides a representation The OS Manages  Execution of ApplicationsResources are made available to multiple What is a “process”?A program in executionAn instance of a program running Process ElementsA process is comprised of:Program code (possibly shared)A set of dataA Process ElementsWhile the process is running it has a number of elements Process Control BlockContains the process elementsCreated and manage by the operating systemAllows support for multiple processes Trace of the ProcessThe behavior of an individual process is shown by Process ExecutionConsider three processes being executedAll are in memory (plus the dispatcher)Lets Trace from the  processes point of view:Each process runs to completion Trace from Processors  point of viewTimeoutI/OTimeoutTimeout RoadmapHow are processes represented and controlled by the OS. Process states which Two-State Process ModelProcess may be in one of two statesRunningNot-running Queuing DiagramEtc … processes moved by the dispatcher of the OS to Process Birth and DeathSee tables 3.1 and 3.2 for more Process CreationThe OS builds a data structure to manage the processTraditionally, the Process TerminationThere must be some way that a process can indicate completion.This Five-State  Process Model Using Two Queues Multiple Blocked Queues Suspended ProcessesProcessor is faster than I/O so all processes could be waiting One Suspend State Two Suspend States Reason for Process SuspensionTable 3.3 Reasons for Process Suspension RoadmapHow are processes represented and controlled by the OS. Process states which Processes  and Resources Operating System  Control StructuresFor the OS is to manage processes and OS Control Tables Memory TablesMemory tables are used to keep track of both main and I/O TablesUsed by the OS to manage the I/O devices and channels File TablesThese tables provide information about:Existence of filesLocation on secondary memoryCurrent Statusother Process TablesTo manage processes the OS needs to know details of the Process AttributesWe can group the process control block information into three general Process IdentificationEach process is assigned a unique numeric identifier.Many of the other Processor State  InformationThis consists of the contents of processor registers. User-visible Pentium II  EFLAGS RegisterAlso see Table 3.6 Process Control InformationThis is the additional information needed by the OS to Structure of Process  Images in Virtual Memory Role of the  Process Control BlockThe most important data structure in RoadmapHow are processes represented and controlled by the OS. Process states which Modes of ExecutionMost processors support at least two modes of executionUser modeLess-privileged Process CreationOnce the OS decides to create a new process it:Assigns a Switching ProcessesSeveral design issues are raised regarding process switchingWhat events trigger a When to switch processesTable 3.8 Mechanisms for Interrupting the Execution of a Change of  Process State …The steps in a process switch are:Save Change of  Process State cont…Select another process for executionUpdate the process Is the OS a Process?If the OS is just a collection of Execution of the  Operating System Non-process KernelExecute kernel outside of any processThe concept of process is considered Execution Within  User ProcessesExecution Within User ProcessesOperating system software within context Process-based  Operating SystemProcess-based operating systemImplement the OS as a collection of system process Security IssuesAn OS associates a set of privileges with each process.Highest level System access threatsIntrudersMasquerader (outsider)Misfeasor (insider)Clandestine user (outside or insider)Malicious software (malware) Countermeasures:  Intrusion DetectionIntrusion detection systems are typically designed to detect human Countermeasures:  AuthenticationTwo Stages:IdentificationVerificationFour Factors:Something the individual knowsSomething the individual possessesSomething the Countermeasures:  Access ControlA policy governing access to resourcesA security administrator maintains Countermeasures:  FirewallsTraditionally, a firewall is a dedicated computer that:interfaces with computers RoadmapHow are processes represented and controlled by the OS. Process states which Unix SVR4 System V Release 4Uses the model of fig3.15b where most UNIX Process State Transition Diagram UNIX Process States A Unix ProcessA process in UNIX is a set of data structures Process CreationProcess creation is by means of the kernel system call,fork( ).This Process Creation  cont…Increment the counters for any files owned by the After CreationAfter creating the process the Kernel can do one of the
Слайды презентации

Слайд 2 Roadmap
How are processes represented and controlled by the

RoadmapHow are processes represented and controlled by the OS. Process states

OS.
Process states which characterize the behaviour of processes.


Data structures used to manage processes.
Ways in which the OS uses these data structures to control process execution.
Discuss process management in UNIX SVR4.

Слайд 3 Requirements of an Operating System
Fundamental Task: Process Management
The Operating

Requirements of an Operating SystemFundamental Task: Process ManagementThe Operating System mustInterleave

System must
Interleave the execution of multiple processes
Allocate resources to

processes, and protect the resources of each process from other processes,
Enable processes to share and exchange information,
Enable synchronization among processes.

Слайд 4 Concepts
From earlier chapters we saw:
Computer platforms consists of

ConceptsFrom earlier chapters we saw:Computer platforms consists of a collection of

a collection of hardware resources

Computer applications are developed to

perform some task

It is inefficient for applications to be written directly for a given hardware platform



Слайд 5 Concepts cont…
OS provides an interface for applications to

Concepts cont…OS provides an interface for applications to useOS provides a

use

OS provides a representation of resources that can be

requested and accessed by application



Слайд 6 The OS Manages Execution of Applications
Resources are made

The OS Manages Execution of ApplicationsResources are made available to multiple

available to multiple applications
The processor is switched among multiple

application
The processor and I/O devices can be used efficiently


Слайд 7 What is a “process”?
A program in execution
An instance

What is a “process”?A program in executionAn instance of a program

of a program running on a computer
The entity that

can be assigned to and executed on a processor
A unit of activity characterized by the execution of a sequence of instructions, a current state, and an associated set of system instructions

Слайд 8 Process Elements
A process is comprised of:
Program code (possibly

Process ElementsA process is comprised of:Program code (possibly shared)A set of

shared)
A set of data
A number of attributes describing the

state of the process

Слайд 9 Process Elements
While the process is running it has

Process ElementsWhile the process is running it has a number of

a number of elements including
Identifier
State
Priority
Program counter
Memory pointers
Context data
I/O status

information
Accounting information

Слайд 10 Process Control Block
Contains the process elements
Created and manage

Process Control BlockContains the process elementsCreated and manage by the operating systemAllows support for multiple processes

by the operating system
Allows support for multiple processes


Слайд 11 Trace of the Process
The behavior of an individual

Trace of the ProcessThe behavior of an individual process is shown

process is shown by listing the sequence of instructions

that are executed
This list is called a Trace
Dispatcher is a small program which switches the processor from one process to another


Слайд 12 Process Execution
Consider three processes being executed
All are in

Process ExecutionConsider three processes being executedAll are in memory (plus the

memory (plus the dispatcher)
Lets ignore virtual memory for this.


Слайд 13 Trace from the processes point of view:
Each process

Trace from the processes point of view:Each process runs to completion

runs to completion


Слайд 14 Trace from Processors point of view
Timeout
I/O
Timeout
Timeout

Trace from Processors point of viewTimeoutI/OTimeoutTimeout

Слайд 15 Roadmap
How are processes represented and controlled by the

RoadmapHow are processes represented and controlled by the OS. Process states

OS.
Process states which characterize the behaviour of processes.


Data structures used to manage processes.
Ways in which the OS uses these data structures to control process execution.
Discuss process management in UNIX SVR4.

Слайд 16 Two-State Process Model
Process may be in one of

Two-State Process ModelProcess may be in one of two statesRunningNot-running

two states
Running
Not-running


Слайд 17 Queuing Diagram
Etc … processes moved by the dispatcher

Queuing DiagramEtc … processes moved by the dispatcher of the OS

of the OS to the CPU then back to

the queue until the task is competed

Слайд 18 Process Birth and Death
See tables 3.1 and 3.2

Process Birth and DeathSee tables 3.1 and 3.2 for more

for more


Слайд 19 Process Creation
The OS builds a data structure to

Process CreationThe OS builds a data structure to manage the processTraditionally,

manage the process
Traditionally, the OS created all processes
But it

can be useful to let a running process create another
This action is called process spawning
Parent Process is the original, creating, process
Child Process is the new process


Слайд 20 Process Termination
There must be some way that a

Process TerminationThere must be some way that a process can indicate

process can indicate completion.
This indication may be:
A HALT instruction

generating an interrupt alert to the OS.
A user action (e.g. log off, quitting an application)
A fault or error
Parent process terminating

Слайд 21 Five-State Process Model

Five-State Process Model

Слайд 22 Using Two Queues

Using Two Queues

Слайд 23 Multiple Blocked Queues

Multiple Blocked Queues

Слайд 24 Suspended Processes
Processor is faster than I/O so all

Suspended ProcessesProcessor is faster than I/O so all processes could be

processes could be waiting for I/O
Swap these processes to

disk to free up more memory and use processor on more processes
Blocked state becomes suspend state when swapped to disk
Two new states
Blocked/Suspend
Ready/Suspend


Слайд 25 One Suspend State

One Suspend State

Слайд 26 Two Suspend States

Two Suspend States

Слайд 27 Reason for Process Suspension
Table 3.3 Reasons for Process

Reason for Process SuspensionTable 3.3 Reasons for Process Suspension

Suspension


Слайд 28 Roadmap
How are processes represented and controlled by the

RoadmapHow are processes represented and controlled by the OS. Process states

OS.
Process states which characterize the behaviour of processes.


Data structures used to manage processes.
Ways in which the OS uses these data structures to control process execution.
Discuss process management in UNIX SVR4.

Слайд 29 Processes and Resources

Processes and Resources

Слайд 30 Operating System Control Structures
For the OS is to

Operating System Control StructuresFor the OS is to manage processes and

manage processes and resources, it must have information about

the current status of each process and resource.
Tables are constructed for each entity the operating system manages


Слайд 31 OS Control Tables

OS Control Tables

Слайд 32 Memory Tables
Memory tables are used to keep track

Memory TablesMemory tables are used to keep track of both main

of both main and secondary memory.
Must include this

information:
Allocation of main memory to processes
Allocation of secondary memory to processes
Protection attributes for access to shared memory regions
Information needed to manage virtual memory

Слайд 33 I/O Tables
Used by the OS to manage the

I/O TablesUsed by the OS to manage the I/O devices and

I/O devices and channels of the computer.
The OS needs

to know
Whether the I/O device is available or assigned
The status of I/O operation
The location in main memory being used as the source or destination of the I/O transfer


Слайд 34 File Tables
These tables provide information about:
Existence of files
Location

File TablesThese tables provide information about:Existence of filesLocation on secondary memoryCurrent

on secondary memory
Current Status
other attributes.
Sometimes this information is maintained

by a file management system


Слайд 35 Process Tables
To manage processes the OS needs to

Process TablesTo manage processes the OS needs to know details of

know details of the processes
Current state
Process ID
Location in

memory
etc
Process control block
Process image is the collection of program. Data, stack, and attributes

Слайд 36 Process Attributes
We can group the process control block

Process AttributesWe can group the process control block information into three

information into three general categories:
Process identification
Processor state information
Process control

information

Слайд 37 Process Identification
Each process is assigned a unique numeric

Process IdentificationEach process is assigned a unique numeric identifier.Many of the

identifier.
Many of the other tables controlled by the OS

may use process identifiers to cross-reference process tables


Слайд 38 Processor State Information
This consists of the contents of

Processor State InformationThis consists of the contents of processor registers. User-visible

processor registers.
User-visible registers
Control and status registers
Stack pointers
Program status

word (PSW)
contains status information
Example: the EFLAGS register on Pentium processors


Слайд 39 Pentium II EFLAGS Register
Also see Table 3.6

Pentium II EFLAGS RegisterAlso see Table 3.6

Слайд 40 Process Control Information
This is the additional information needed by

Process Control InformationThis is the additional information needed by the OS

the OS to control and coordinate the various active

processes.
See table 3.5 for scope of information


Слайд 41 Structure of Process Images in Virtual Memory

Structure of Process Images in Virtual Memory

Слайд 42 Role of the Process Control Block
The most important

Role of the Process Control BlockThe most important data structure in

data structure in an OS
It defines the state

of the OS
Process Control Block requires protection
A faulty routine could cause damage to the block destroying the OS’s ability to manage the process
Any design change to the block could affect many modules of the OS


Слайд 43 Roadmap
How are processes represented and controlled by the

RoadmapHow are processes represented and controlled by the OS. Process states

OS.
Process states which characterize the behaviour of processes.


Data structures used to manage processes.
Ways in which the OS uses these data structures to control process execution.
Discuss process management in UNIX SVR4.

Слайд 44 Modes of Execution
Most processors support at least two

Modes of ExecutionMost processors support at least two modes of executionUser

modes of execution
User mode
Less-privileged mode
User programs typically execute in

this mode
System mode
More-privileged mode
Kernel of the operating system

Слайд 45 Process Creation
Once the OS decides to create a

Process CreationOnce the OS decides to create a new process it:Assigns

new process it:
Assigns a unique process identifier
Allocates space for

the process
Initializes process control block
Sets up appropriate linkages
Creates or expand other data structures


Слайд 46 Switching Processes
Several design issues are raised regarding process

Switching ProcessesSeveral design issues are raised regarding process switchingWhat events trigger

switching
What events trigger a process switch?
We must distinguish

between mode switching and process switching.
What must the OS do to the various data structures under its control to achieve a process switch?

Слайд 47 When to switch processes
Table 3.8 Mechanisms for Interrupting

When to switch processesTable 3.8 Mechanisms for Interrupting the Execution of

the Execution of a Process
A process switch may occur

any time that the OS has gained control from the currently running process. Possible events giving OS control are:

Слайд 48 Change of Process State …
The steps in a

Change of Process State …The steps in a process switch are:Save

process switch are:
Save context of processor including program counter

and other registers
Update the process control block of the process that is currently in the Running state
Move process control block to appropriate queue – ready; blocked; ready/suspend


Слайд 49 Change of Process State cont…
Select another process for

Change of Process State cont…Select another process for executionUpdate the process

execution
Update the process control block of the process selected
Update

memory-management data structures
Restore context of the selected process


Слайд 50 Is the OS a Process?
If the OS is

Is the OS a Process?If the OS is just a collection

just a collection of programs and if it is

executed by the processor just like any other program, is the OS a process?
If so, how is it controlled?
Who (what) controls it?

Слайд 51 Execution of the Operating System

Execution of the Operating System

Слайд 52 Non-process Kernel
Execute kernel outside of any process
The concept

Non-process KernelExecute kernel outside of any processThe concept of process is

of process is considered to apply only to user

programs
Operating system code is executed as a separate entity that operates in privileged mode


Слайд 53 Execution Within User Processes
Execution Within User Processes
Operating system

Execution Within User ProcessesExecution Within User ProcessesOperating system software within context

software within context of a user process
No need for

Process Switch to run OS routine


Слайд 54 Process-based Operating System
Process-based operating system
Implement the OS as

Process-based Operating SystemProcess-based operating systemImplement the OS as a collection of system process

a collection of system process


Слайд 55 Security Issues
An OS associates a set of privileges

Security IssuesAn OS associates a set of privileges with each process.Highest

with each process.
Highest level being administrator, supervisor, or root,

access.
A key security issue in the design of any OS is to prevent anything (user or process) from gaining unauthorized privileges on the system
Especially - from gaining root access.




Слайд 56 System access threats
Intruders
Masquerader (outsider)
Misfeasor (insider)
Clandestine user (outside or

System access threatsIntrudersMasquerader (outsider)Misfeasor (insider)Clandestine user (outside or insider)Malicious software (malware)

insider)
Malicious software (malware)


Слайд 57 Countermeasures: Intrusion Detection
Intrusion detection systems are typically designed

Countermeasures: Intrusion DetectionIntrusion detection systems are typically designed to detect human

to detect human intruder and malicious software behaviour.
May be

host or network based
Intrusion detection systems (IDS) typically comprise
Sensors
Analyzers
User Interface


Слайд 58 Countermeasures: Authentication
Two Stages:
Identification
Verification
Four Factors:
Something the individual knows
Something the

Countermeasures: AuthenticationTwo Stages:IdentificationVerificationFour Factors:Something the individual knowsSomething the individual possessesSomething the

individual possesses
Something the individual is (static biometrics)
Something the individual

does (dynamic biometrics)


Слайд 59 Countermeasures: Access Control
A policy governing access to resources
A

Countermeasures: Access ControlA policy governing access to resourcesA security administrator maintains

security administrator maintains an authorization database
The access control function

consults this to determine whether to grant access.
An auditing function monitors and keeps a record of user accesses to system resources.


Слайд 60 Countermeasures: Firewalls
Traditionally, a firewall is a dedicated computer

Countermeasures: FirewallsTraditionally, a firewall is a dedicated computer that:interfaces with computers

that:
interfaces with computers outside a network
has special security

precautions built into it to protect sensitive files on computers within the network.


Слайд 61 Roadmap
How are processes represented and controlled by the

RoadmapHow are processes represented and controlled by the OS. Process states

OS.
Process states which characterize the behaviour of processes.


Data structures used to manage processes.
Ways in which the OS uses these data structures to control process execution.
Discuss process management in UNIX SVR4.

Слайд 62 Unix SVR4 System V Release 4
Uses the model of

Unix SVR4 System V Release 4Uses the model of fig3.15b where

fig3.15b where most of the OS executes in the

user process
System Processes - Kernel mode only
User Processes
User mode to execute user programs and utilities
Kernel mode to execute instructions that belong to the kernel.




Слайд 63 UNIX Process State Transition Diagram

UNIX Process State Transition Diagram

Слайд 64 UNIX Process States

UNIX Process States

Слайд 65 A Unix Process
A process in UNIX is a

A Unix ProcessA process in UNIX is a set of data

set of data structures that provide the OS with

all of the information necessary to manage and dispatch processes.
See Table 3.10 which organizes the elements into three parts:
user-level context,
register context, and
system-level context.

Слайд 66 Process Creation
Process creation is by means of the

Process CreationProcess creation is by means of the kernel system call,fork(

kernel system call,fork( ).
This causes the OS, in Kernel

Mode, to:
Allocate a slot in the process table for the new process.
Assign a unique process ID to the child process.
Copy of process image of the parent, with the exception of any shared memory.

Слайд 67 Process Creation cont…
Increment the counters for any files

Process Creation cont…Increment the counters for any files owned by the

owned by the parent, to reflect that an additional

process now also owns those files.
Assign the child process to the Ready to Run state.
Returns the ID number of the child to the parent process, and a 0 value to the child process.



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