Operating Systems ( )

Transcription

1 Operating Systems ( ) Itai Dinur Office: Alon, 224 Office hours: Wednesday, 16:00-18:00 Danny Hendler Office: Alon, 218 Office hours: Wednesday, 13:00-15:00 Robert Iakobashvili Office: Alon, 316 Office hours: Sundays, 18:00-19:00 Lecturers: Itai Dinur, Danny Hendler and Robert Iakobashvili TAs: Ariel Talmi, Or Dinari, Ahmad Drobi, Matan Drory, Tshai Saporta and Roy Uziel Course site: 1

2 Assignments and grade structure Assignment Programming Programming Midterm (not mandatory) Final Subject Scheduling + Synchronization Memory Management + Files Processes, scheduling, synchronization, memory (TBD) All Weight 15% 15% 15% (0%) 55% (70%) Assignments and exams are mandatory Must pass final exam 2

3 Textbooks A. Tanenbaum: Modern Operating Systems, Prentice-Hall, 4 th Edition, 2015 A. Silbetschatz et al.: Operating System Concepts (9th ed.), Addison Wesley, 2012 G. Nutt: Operating Systems (a modern perspective) (3rd ed.), Addison Wesley, 2003 W. Stallings: Operating Systems (6th ed.), Prentice-Hall, 2009

4 Syllabus 1. Introduction - History; Views; Concepts; Structure 2. Process Management - Processes; State + Resources; Threads; Unix implementation of Processes 3. Scheduling Paradigms; Unix; Modeling 4. Synchronization - Synchronization primitives and their equivalence; Deadlocks 5. Memory Management - Virtual memory; Page replacement algorithms; Segmentation 6. File Systems - Implementation; Directory and space management; Unix file system; Distributed file systems (NFS) 7. Virtualization Virtual machines, type I and II hypervisors, classic virtualization, sensitive and privileged instructions, binary translation, memory virtualization 7. Distributed Synchronization (if there's time)

5 Introduction: outline What is an operating system? Some history OS concepts

6 Layered Hardware-Software Machine Model

7 What is an Operating System? An operating system is: 1. An Extended Machine 2. A Resource manager

8 Computer-System Architecture

9 Operating Systems as extended Machines The problems: Bare machine has complex structure o Processors o Many difficult-to-program devices Primitive Instruction Set Different for Different Machines OS provides: Abstraction! Simple, easier to use interface (machine-independent) Hiding of unnecessary details

10 OS abstraction example: read from disk Read file data from disk (simplified) Read linear sector 17,403 from disk 2 Convert linear sector number to: cylinder, sector, head (may be complicated outer cylinders have more sectors, bad sectors remapped, etc.) Move disk arm to requested cylinder Wait for proper sector to appear OS abstraction return-code = read(fd, buff, nbytes)

11 UNIX high-level architecture User Interface

12 Operating Systems as Resource Managers Multiple resources o Processors; Memory o Disks; Tapes; Printers o Network interfaces; Terminals Controlled allocation of Resources among: o Groups, Users; Processes, Threads, Means of control: sharing/multiplexing/scheduling, monitoring, protection, report/payment

13 Introduction: outline What is an operating system? Some history OS concepts

14 History of Operating Systems First generation o vacuum tubes, plug boards user plugs-in program

15 The first computers Electronic Numerical Integrator And Computer (ENIAC) Mathematical Analyzer, Numeric Integrator And Computer(MANIAC)

16 History of Operating Systems (cont d) Second generation o transistors, batch systems multiple programs on Disk Third generation o ICs and multiprogramming - user interaction (time-sharing) Fourth generation 1980 present o personal computers graphic user-interface o Networks file & computing services o Mobile computing - Cellular phones, Cloud computing

17 Punched-cards job example Second generation o transistors, batch systems multiple programs on Disk

18 History of Operating Systems (cont d) Second generation o transistors, batch systems multiple programs on Disk Third generation o ICs and multiprogramming - user interaction (time-sharing) Fourth generation 1980 present o personal computers graphic user-interface o Networks file & computing services o Mobile computing - Cellular phones, Cloud computing

19 How Bill Gates became rich 1974: Intel releases the 8080 processor, needs an OS Please! develop an OS CP/M OS Gary Kildall

20 How Bill Gates became rich (cont d) 1974: Intel releases the 8080 processor, needs an OS CP/M OS Can you grant me CP/M rights? Sure! Gary Kildall

21 How Bill Gates became rich (cont d) 1980: IBM designs IMB PC, needs an OS Can you find an OS for our PC? Please meet IBM, they need an OS Gary Kildall

22 How Bill Gates became rich (cont d) 1980: IBM designs IMB PC, needs an OS Kildall too busy. Please develop an OS! I de like to buy the DOS OS Sure, it s yours for $75,000

23 How Bill Gates became rich (cont d) 1980: IBM designs IMB PC, needs an OS May I retain the rights for MS- DOS? Sure, why not!!

24 How Bill Gates became rich (cont d) Well, this is 20:20 hind vision

25 Introduction: outline What is an operating system? Some history OS concepts

26 OS Key Functions Process management o process creation; deletion; suspension/preemption o process synchronization; communication; scheduling Main-memory management o Manage used parts and their current users o Select processes to load from secondary storage o Allocate memory to running processes Secondary storage management o Free-space management o Storage allocation

27 OS Key Functions (cont d) File system management o File + directory - creation; deletion o File manipulation primitives o Mapping files onto secondary storage I/O system management o General device-driver interface o Drivers for specific hardware devices Protection system o Distinguish between authorized and unauthorized usage o Provide means of enforcement

28 Processes - a key concept Resource container for program in execution Timesharing, process suspension/preemption Process Table Process Groups Signals

29 Why do we need multiple processes? Single application: We want things to happen concurrently (E.g.: paging and typing in a text editor) Multiple applications: processes running in the background (e.g., Anti Virus) Multiple users: The departmental computer; all types of Servers

30 Multiprogramming: how is it done? CPU much faster than I/O o Computation/communication overlap Memory large enough requires memory protection! Scheduler which manages flow of jobs in and out and shares CPU between jobs requires Timer

31 Process trees A process tree A created two child processes, B and C B created three child processes, D, E, and F

32 Inter-Process Communication (IPC) Two processes communicating via a pipe

33 Files: non volatile data File types and operations on files Directories - hierarchical structure Working directories Root directory Students Faculty Amnon Gil Roni Or Papers Progs Grants

34 Files: non volatile data (cont d) Protection and Security Unix - user; group; other (rwx bits) File descriptors (handles) I/O as a special file Block & Character special files Standard input; output; error Pipes Links

35 I/O is performed in kernel mode All I/O instructions are privileged instructions I/O devices and CPU can execute concurrently CPU moves data between main memory and device controllers' buffers (done by device drivers) Device controllers interrupt upon completion Interrupt handler runs in kernel mode

36 Steps in performing I/O

37 Driver initiates operation Steps in performing I/O

38 Steps in performing I/O Device signals interrupt controller

39 Interrupt controller notifies CPU Steps in performing I/O

40 Interrupt controller writes device number Steps in performing I/O

41 Steps in performing I/O CPU starts handling interrupt

42 Steps in performing I/O Appropriate interrupt handler called

43 Steps in performing I/O Execution resumed

44 Interrupts and the fetch-decode-execute loop Do forever{ IR = memory[pc]; execute(ir); PC++; If(Interrupt_Request) { memory[0] = PC; PC = memory[1] } } An interrupt is an asynchronous event The kernel interrupt handling routine may use a disable_interrupts instruction to avoid losing data while processing an interrupt request Interrupt handler is typically called indirectly via the interrupt vector

45 Synchronous vs. Asynchronous I/O execute

46 Steps in Making a System Call There are 11 steps in making the system call: read (fd, buffer, nbytes) Is this call Synchronous or Asynchronous?

47 System Calls processes files directories miscellaneous

48 The Shell Command Language sort < file1 > file2 cat file1 sort lpr The Shell is a process which executes its commands as offspring processes Processes may call shell commands by using the system system call

49 Shell structure Parent & child A stripped-down shell: while (TRUE) { /* repeat forever */ type_prompt( ); /* display prompt */ read_command (command, parameters) /* input from terminal */ } if (fork() > 0) { /* fork off child process */ /* Parent code */ wait(); /* wait for child to exit */ } else { /* Child code */ execvp (command, parameters); /* execute command */ }

50 Linux Shell initialization The init program (process 1) runs getty on all ports Upon detecting a terminal, getty runs login Typing in a user name and a password login checks the passwd file and if correct runs a shell the one specified in the UID entry The shell is run with that user ID environment parameters

51 Running user commands User types: grep some_word file_name Shell parses the command, inserts the strings grep, some_word, file_name into argv and their number to argc Next, the shell uses fork() to create a process (same user ID) Now, it takes the executable name grep and the arguments, all from argv, and uses execvp() (or a similar system call) to run the grep executable On foreground execution, the shell would use the wait() system call and continue its session only after the child process terminates

52 UNIX Utility Programs A few of the more common UNIX utility programs required by POSIX