CS考试辅导 CSCI 4061 Introduction to Operating Systems – cscodehelp代写

CSCI 4061 Introduction to Operating Systems
Instructor:
Today
 OS Overview
 OS Structure and APIs  Unix Overview
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What is an Operating System?
 User’s View: Extended Machine
 Programmer’s View: Resource Manager  System View: Control Program
Applications
Operating System
Hardware
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User’s View
 Extended Machine
 Simple abstraction of hardware resources
 CPU -> Processes, Threads
 Memory -> Virtual Memory
 Disks -> Files
 Network interfaces -> Sockets
 Goal: Simple, easy to use
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Programmer’s View
 Resource Manager
 Efficient division of resources among multiple users, programs
 Multiple processes on same CPU
 Multiple files on the same disk
 Multiple connections on same network link
 Arbitrate conflicting demands
 Goal: Maximize system performance
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System View
 Control Program
 Handle different events, user inputs, etc.
 User typing commands on keyboard
 Bytes being read from the disk
 Packets arriving on the network interface
 Multiple concurrent and asynchronous events  Goal: Ensure correctness and fairness
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What services does the OS provide?
 Allows different applications to execute concurrently
 Processes, Memory management
 Allows access to multiple files, user input, display
 File system, File I/O
 Allows parallelism and data sharing
 Threads and synchronization
 Enables communication across machines
 Networking and sockets
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Course Road Map
 Understand different OS components  Processes
 File System
 Memory Management  Threads
 Concurrency and Communication  Thread Synchronization
 Networking and IPC
 Signals
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General Operating System Structure
 Hardware-OS interactions  OS-Application interactions
Applications
Operating System
Hardware
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Kernel
 Core of the Operating System
 Provides the main functionality:
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 Process and Thread Management  Memory Management
 File System and I/O
 Inter-Process Communication
Hardware-OS interactions
 We would mainly worry about hardware abstractions
 E.g.: Processes, files, virtual memory, sockets  Control allocation and management of CPU, disks, devices, memory, network interfaces
 Portability across variety of hardware
 Asynchronous events and concurrency. E.g.: interrupts, I/O events
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OS-Application interactions
 Shells and User interfaces
 Allow users to interact with the OS
 Libraries
 Allow programs to use common services
 System calls
 Direct conduit into the OS
 Signals
 OS interacting with user programs
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Key Questions
 Q.1: How does the OS protect the hardware from (unruly or malicious) applications?
 Q.2: How do applications get access to desired resources (CPU, memory, disk, etc.)?
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Kernel Mode
User Mode
Kernel Mode
 OS runs in kernel mode: hardware-enabled  Higher privileges than user mode
 Access to hardware resources  Access to protected memory  Access to OS data structures
 Tighter control, security of system resources 14
Applications
Operating System
User Mode
User Mode
Kernel Mode
 Applications, utilities, shell run in user mode  Restricted access to
 System resources
 Kernel data structures  Protection boundaries
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Applications
Operating System
Application-OS Interaction: Example Scenario
 Suppose an application needs to read data from a file
 How does the application tell the OS to read the data for it?
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System Calls
User Mode
System Call Result Kernel Mode
 Kernel API: well-defined, small set of operations  Entry points into the kernel
 Provide restricted access to the kernel
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Applications
Operating System
System Call Operation
 User program executes a TRAP instruction  Switches to kernel mode
 Passes parameters, system call no.
 Kernel looks up system call table  System call handler is invoked
 Results returned to user program
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User Mode Kernel Mode
Parameters, Syscall no.
Result
Trap Syscall Table Dispatcher
Syscall Call Example: read
 E.g.: read 16 bytes from file F into buffer  Parameters: (F, buffer, 16)
 User program passes:
 Parameters, read syscall no. (3)
 User program executes TRAP
 Kernel looks up code for syscall no. 3
 Kernel executes code for read system call
 Look up F (File system)
 Transfer 16 bytes from disk to buffer (I/O)  System call returns control to user space
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System Call Implementation
 Requires performing TRAP instruction  Requires passing parameters to kernel
 In registers or in buffers
 Requires getting back control from kernel  May be implemented in assembly language
 How to use in programs easily?
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Libraries
 Pre-written and pre-tested functions
 Programmers can call library functions in their
programs  Two types:
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 Wrappers for system calls. E.g.: read library call
 User-level utility functions. E.g.: String operations (strcpy, strcmp, strlen, …)
Unix Overview
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What is Unix?
 Highly Popular OS
 Programming Platform/Toolbox  Many variants exist
 Multiple implementations, similar functionality  Principles:
 Multiprogramming  Flexibility
 Extensibility
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Unix Evolution
 MULTICS (1965): MULTiplexed Information and Computing Service
 UNIX (1969): Developed at Bell Labs  Developed in C
 Architecture-independent
 Several Evolution Paths:
 AT&T System V (1983) -> SCO Unix
 BSD (1980) -> FreeBSD, NetBSD
 Linux (1991-) -> Android
 Other variants: Solaris, HP/UX, IBM AIX, S/X
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Common Features and Variations
 Common:
 Similar APIs and basic tools  POSIX Standards
 Variations:
 Underlying implementation
 Shells, tools, and user interfaces
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Operating System Structure
Applications
Operating System
Hardware
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Unix Structure
Applications, Utilities, and User Programs
Shell
Libraries
System Call Interface
Kernel
CPU, Memory, Disks, Devices
AUI (Application User Interface)
API (Application Programmer Interface)
Operating System
Hardware
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Shell
 Basic interface to the OS
 Allows users to interact with the OS
 Command interpreter
 Parses and executes several commands
 Many Unix Shells
 Bourne sh, csh, tcsh, ksh, bash
 Shell is just another user-level program  No special privileges
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Shell as Command Interpreter
 Read-eval-print
 Read user input
 Evaluate the input and execute command(s)  Print output
 Example: ls –l
 User types above command
 Shell reads and parses the input
 Shell invokes “ls” program with argument “-l”  Shell prints the output produced by the program
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Standard I/O
 Standard input (stdin): source of input data for a command or program
 Default: Keyboard
 Standard output (stdout): destination of output
from a command or program  Default: Display
 Standard error (stderr): destination of error messages
 Default: Display
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Shell Redirection
 Redirect the input or output of a command to a file
 Input redirection (<): Takes input from a file instead of keyboard  sort < file  Output redirection (>): Send output to a file instead of display
ls -l > file
 cat file1 >> file2
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Shell Plumbing
 Pipes: prog1 | prog2
 Allow multiple commands to be linked together
 Connects output of prog1 to input of prog2
 Examples:
ls -l | more
 cat foo | sort | head
 How will you do the above using only redirection?
 Most UNIX commands consume and produce plain text data
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Unix File System
 Tree-based hierarchy
 File system has a root (/)
 Each user has a home directory ($HOME)  There are several standard directories:
 E.g.: /bin (binary files), /dev: device files, /lib: libraries, …
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Unix Directory Hierarchy
/
bin dev etc home lib usr tmp var
cp ls
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chandra
bin myprog
cc
bin include lib
which libc.so libm.so
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