Silberschatz, Galvin and Gagne 2002 Modified for CSCI 346, Royden, 2011 3.1 Operating System...
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Transcript of Silberschatz, Galvin and Gagne 2002 Modified for CSCI 346, Royden, 2011 3.1 Operating System...
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.1Operating System Concepts
Operating Systems
Lecture 4System Calls
OS System Structure
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.2
Computing Environments Traditional Computing Client-Server Computing Peer to Peer Computing (e.g. Napster) Web-based Computing Special Purpose Systems:
Embedded Systems Multimedia Systems Handheld Systems
Operating System Concepts
Client Server Computing
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.3
User-Operating System Interface Command Line Interpreter (CLI) (e.g. UNIX or MS-DOS)
Fetches command from user and executes Commands may be built into O.S. or names of programs to
execute.
Operating System Concepts
Bourne Shell Command Interpreter for Solaris
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.4
User-Operating System Interface--GUI
GUI uses desktop metaphor with Icons for files and folders. Actions executed with mouse-over and button-clicks. Many systems provide both CLI and GUI (e.g. LINUX has
desktop environment, Apple UNIX shell, Windows has CLI shell).
Operating System Concepts
Mac OS X GUI
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.5Operating System Concepts
System Calls
System calls provide the interface between a running program and the operating system.Generally available as assembly-language
instructions. Languages defined to replace assembly language for
systems programming allow system calls to be made directly (e.g., C, C++)
Use API's so don't need to know system details. (Win32, POSIX, Java)
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.6Operating System Concepts
System Calls are Used Frequently
A single program may make numerous system calls. For example, a program to read from one file and write to another would need system calls for the following:(We will discuss this in class)Prompt the user to enter file namesRead in filenamesOpen input fileRead from input fileOpen/create output fileWrite output to fileClose input and output files
The system must be able to signal and handle errors that occur.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.7Operating System ConceptsOperating System Concepts
C program invoking printf() library call, which calls write() system call
API system call
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.8Operating System Concepts
Passing Parameters
Three general methods are used to pass parameters between a running program and the operating system.Pass parameters in registers.Store the parameters in a table in memory,
and the table address is passed as a parameter in a register.
Push (store) the parameters onto the stack by the program, and pop off the stack by operating system.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.9Operating System Concepts
Passing of Parameters As A Table
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.10Operating System Concepts
Types of System Calls Process control
create (fork), execute (exec), wait, end (exit), abort (kill), etc. File management (Can you think of any in Linux?)
create (mkdir), delete (rm, rmdir), open, close, read, write, cp, rm, mkdir, rmdir, ls, cat, more, grep, etc. get/set file attributes
Device management read, write, attach (mount), detach (unmount), get/set device
attributes Information maintenance
get/set time or date, get/set process/device attributes (getpid, du, ps, etc)
Communications send, receive, connect, accept, get/set status information,
gethostid/sethostid, gethostbyname, etc. Protection (Can you think of any?)
get/set file attributes (chmod, chown, chgrp)
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.11Operating System Concepts
Process Control
A process executing one program may want to load and execute another program (e.g. the shell loads and executes programs). The following are important considerations:
Where does control return when the new process is finished? If return control to existing program, must save memory image
of existing program before loading new process. If both programs are to run concurrently, the new process is
added to the multiprogramming set of processes. Controlling execution of the process:
get/set process attributes, terminate process Waiting for the process to finish
wait event, signal event Terminating the process
Normal (exit) or abnormal (abort) termination. There are multiple ways of implementing process control.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.12Operating System Concepts
MS-DOS Execution
At System Start-up Running a Program
MS-DOS runs the command interpreter on startup.
It loads a new program into memory, writing over part of the interpreter.
When the program terminates, the part of the interpreter not overwritten begins execution. It loads the rest of the interpreter from disk.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.13Operating System Concepts
UNIX Running Multiple Programs
UNIX runs the shell on startup.
To start a new process, it uses the fork command to create the process and exec to execute it.
If the process is in the foreground, the shell waits for the process to finish.
If the process is in the background, the user can continue to issue commands while the process is running.
When the process is finished, it executes an exit system call.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.14
System Calls--Communication
Operating System Concepts
How is inter-process communication achieved? Message Passing (think USPS):
• Good for small amounts of data• No conflicts (i.e. with protection and
synchronization)• Easier to implement
Shared Memory• Speed• Convenience
Both are common and most systems have both.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.15Operating System Concepts
Message Passing
Processes use message passing to send messages to one another.
First, the connection must be opened. The name of the communicator must be known (host name or
host id, process name or process id). Use get process id or get host id.
open connection, close connection
The recipient uses "accept connection" The initiator is the client. The recipient of the request is
the server. Exchange of information made with write message
system calls.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.16Operating System Concepts
Shared Memory
In memory sharing, processes communicate by writing and reading to the same memory addresses.
Processes use map memory system calls to access memory owned by other processes.
Both processes must agree to remove O.S. memory restriction so that they can access the same region of memory.
The processes are responsible for the form and location of the data.
The processes are responsible for making sure that they are not writing to the same memory area simultaneously.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.17Operating System Concepts
Communication Models
Msg Passing Shared Memory
Communication may take place using either message passing or shared memory.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.18Operating System Concepts
System Programs
System programs provide a convenient environment for program development and execution. The can be divided into: File manipulation (copy, delete, rename, print, list) Status information (get date, disk usage, performance info) File modification (text editors) Programming language support (compilers, interpreters,
debuggers) Program loading and execution (loaders, linkers) Communications (IM, email, remote login) Application programs
Most users’ view of the operation system is defined by system programs, not the actual system calls.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.19
Types of OS Structure
Operating System Concepts
The design of operating systems has evolved over time.We can roughly divide them into the following categories:
1. Monolithic systems (1st operating systems).
2. Modular systems (e.g. early UNIX, Solaris)
3. Hierarchical layered systems (e.g. OS/2)
4. Microkernel systems (e.g. Mach)
5. Virtual Machines
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.20
From monolithic to modular
Operating System Concepts
Monolithic systems: No structure to speak of. As the OS grows, the complexity becomes overwhelming. Example: OS/360 version 1
created by 5000 programmers over 5 years. In 1964, had over 1 million lines of code.
Example: Multics In 1975, had over 20 million lines of code. When UNIX was written, people joked it was EUNUCHS, i.e. a castrated Multics
Modular systems: Divide OS into modules. Example: Original UNIX had 2 modules.
System programs (e.g. emacs, compiler) The kernel (HUGE!)--file system, CPU scheduling, memory management, etc.
Problem: Kernel so big and complex that it was hard to work with and extend.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.21Operating System Concepts
MS-DOS System Structure
MS-DOS – written to provide the most functionality in the least space not divided into modulesAlthough MS-DOS has some structure, its
interfaces and levels of functionality are not well separated
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.22Operating System Concepts
MS-DOS Layer Structure
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.23Operating System Concepts
UNIX System Structure
UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts. Systems programs The kernel
Consists of everything below the system-call interface and above the physical hardware
Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.24Operating System Concepts
UNIX System Structure
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.25Operating System Concepts
Layered Approach
The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.
With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.
Advantage: Modularity makes it easy to modify and extend.
Disadvantage: Some functions may depend on one another, making a strict hierarchy difficult to implement.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.26Operating System Concepts
An Operating System Layer
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.27Operating System Concepts
OS/2 Layer Structure
Jointly developed in the mid 1980's by IBM and MS
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.28
Modules
Operating System Concepts
Most modern operating systems implement kernel modules• Uses object-oriented approach• Each core component is separate• Each talks to the others over known
interfaces• Each is loadable as needed within the
kernel
Overall, similar to layers but with more flexible
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.29
Solaris Modular Approach
Operating System Concepts
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.30Operating System Concepts
Microkernel System Structure
Moves as much from the kernel into “user” space. Communication takes place between user modules
using message passing. Only the kernel is machine/device dependent.
Example: Mac OS X is based on the Mach micro kernel.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.31
Microkernels—Benefits and Drawbacks
Operating System Concepts
Microkernels:Advantages:
Modularity (Easy to modify modules) Extensibility (Can easily add new functions--user processes) Flexibility (Can remove functions that are not needed) Portability (Only the small kernel has hardware specific code) Distributed System support (Message passing can generalize to network communications) Object oriented (A good design).
Disadvantages: (will discuss in class) Performance: create/send receive message takes longer than a system call. Efficiency still a problem.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.32Operating System Concepts
Virtual Machines
Virtual Machines: Provides software interface identical to underlying bare hardware.
Virtual CPU, Virtual Device drivers, Virtual memory, etc. Each process has its own virtual machine Implementation provides interface between virtual machine and real machine. Physical resources divided up between the virtual machines (e.g. minidisks). Advantages: (will discuss in class)
Security (no process has direct access to system resources.) System development (Can use virtual machine to test new OS) System compatibility. Can run Windows on Virtual PC on Mac. Java runs on Java virtual machine--cross platform.
Disadvantage: (will discuss in class) Speed: Each instruction is interpreted. This is slower than a direct system call.
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.33Operating System Concepts
Virtual Machine Diagram
Non-virtual Machine Virtual Machine
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.34
VMWare Architecture
Operating System Concepts
Silberschatz, Galvin and Gagne 2002Modified for CSCI 346, Royden, 2011
3.35Operating System Concepts
Java Virtual Machine
Compiled Java programs are platform-neutral bytecodes executed by a Java Virtual Machine (JVM).
JVM consists of
- class loader
- class verifier
- runtime interpreter
Just-In-Time (JIT) compilers increase performance