CSE Opera+ng System Principles

Transcription

1 CSE Opera+ng System Principles Lecture 3 Systems Structure Project 1 Intro CSE Opera+ng System Principles 2 1

2 Recap Last Lecture I/O Structure (I/O Interface, DMA) Storage and Memory Hierarchy Modern CPUs, Symmetric Mul+processing, Clusters Opera+ng System Structure Mul+programming Interrupts Mode bits Process/Memory/Storage Management CSE Opera+ng System Principles 3 Overview What are System Calls? What are System Programs? How is the OS structured? What are Virtual Machines? CSE Opera+ng System Principles 4 2

3 Program Execu+on $ echo 'int main () { return 0; }' > example.c $ gcc example.c $./a.out What services is the OS providing? CSE Opera+ng System Principles 5 A View of Opera+ng System Services CSE Opera+ng System Principles 6 3

4 Opera+ng System Services User interface: Command-line (CLI) terminal, flavors: shells Direct command entry (fetch command, execute it); some commands built-in Graphics User Interface (GUI) User-friendly desktop metaphor interface Batch Program execu+on: Load program into memory, run program, terminate program (normally, abnormally) I/O opera+on: File, I/O devices, etc. CSE Opera+ng System Principles 7 Bourne Shell Command Interpreter CSE Opera+ng System Principles 8 4

5 The Mac OS X GUI CSE Opera+ng System Principles 9 Opera+ng System Services (User) File-system manipula+on: Read/write files/directories, create/delete, search, permission management, etc. Communica+ons: Exchange informa+on on same computer or between computers Shared memory or message passing Error detec+on: Hardware/sogware errors OS should take appropriate ac+ons CSE Opera+ng System Principles 10 5

6 Opera+ng System Services (System) Resource alloca+on Mul+ple users or mul+ple jobs Accoun+ng Which resources are used and how much? Protec+on & Security Protec+on: control all access to system resources Security: protect system from malicious users or jobs CSE Opera+ng System Principles 11 Interfacing with the OS Interrupt Driven! I/O Timer Interrupt User Program Errors Memory Faults CSE Opera+ng System Principles 12 6

7 How Are Interrupts Handled? Fetch Decode Execute Handle Interrupts 0x00: PCI Intr 0 0x08: PCI Intr 1 0x10: Memory Fault 0x18: Timer Intr CSE Opera+ng System Principles 13 Interrupts: System Calls Interrupt to request OS services! Special interrupt (for all syscalls) (0x80 on Unix) Programming interface, typically wrijen in highlevel language (C, C++) Typically wrapped in Applica+on Programming Interface (API) rather than direct syscalls Win32 API, POSIX (Portable OS Interface for Unix), Java API (Java VM) CSE Opera+ng System Principles 14 7

8 Why APIs? Portability Cleaner (parameters) Combine mul+ple system calls CSE Opera+ng System Principles 15 System Call API UNIX/POSIX ssize_t write(int fildes, const void *buf, size_t nbyte); int open(const char *path, int oflag,... ); WINDOWS BOOL ReadFile ( HANDLE hfile, LPVOID lpbuffer, DWORD nnumberofbytestoread, LPDWORD lpnumberofbytesread, LPOVERLAPPED lpoverlapped ); CSE Opera+ng System Principles 16 8

9 API System Call OS Rela+onship CSE Opera+ng System Principles 17 Standard C Library Example CSE Opera+ng System Principles 18 9

10 System Call Parameters Most system calls require arguments, like a C func+on! Three general methods used to pass parameters to the OS Simplest: pass the parameters in registers In some cases, may be more parameters than registers Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register This approach taken by Linux and Solaris Parameters placed, or pushed, onto the stack by the program and popped off the stack by the opera+ng system Block and stack methods do not limit the number or length of parameters being passed CSE Opera+ng System Principles 19 Types of System Calls Process control end, abort load, execute create process, terminate process get process ajributes, set process ajributes wait for +me wait event, signal event allocate and free memory File management create file, delete file open, close file read, write, reposi+on get and set file ajributes CSE Opera+ng System Principles 20 10

11 Types of System Calls (cont.) Device management request device, release device read, write, reposi+on get device ajributes, set device ajributes logically ajach or detach devices Informa+on maintenance get +me or date, set +me or date get system data, set system data get and set process, file, or device ajributes Communica+ons Create, delete communica+on connec+on send, receive messages transfer status informa+on ajach and detach remote devices CSE Opera+ng System Principles 21 System Call Examples CSE Opera+ng System Principles 22 11

12 MSDOS (a) At system startup (b) running a program CSE Opera+ng System Principles 23 FreeBSD CSE Opera+ng System Principles 24 12

13 ps $ ps -a -u pdonnel3 PID TTY TIME CMD 9387? 00:00:00 sshd 9388 pts/1 00:00:00 csh 9602? 00:00:00 screen 9603 pts/2 00:00:00 bash 9607 pts/3 00:00:00 bash 16641? 00:00:00 sshd pts/0 00:00:00 csh pts/0 00:00:00 screen pts/3 00:00:00 sudo pts/3 00:00:00 make pts/3 00:00:00 make pts/3 00:00:00 installkernel pts/3 00:00:00 new-kernel-pkg pts/3 00:00:02 depmod pts/4 00:00:00 bash pts/4 00:00:00 ps CSE Opera+ng System Principles 25 System Programs System programs provide a convenient environment for program development and execu+on. They can be divided into: File manipula+on Status informa+on File modifica+on Programming language support Program loading and execu+on Communica+ons Most users view of the opera+on system is defined by system programs, not the actual system calls CSE Opera+ng System Principles 26 13

14 System Programs Most system programs are simply user interfaces to system calls; others are considerably more complex File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories Status informagon Some ask the system for info - date, +me, amount of available memory, disk space, number of users Others provide detailed performance, logging, and debugging informa+on Typically, these programs format and print the output to the terminal or other output devices Some systems implement a registry - used to store and retrieve configura+on informa+on CSE Opera+ng System Principles 27 System Programs File modificagon Text editors Text transforma+on Programming-language support Compilers, assemblers, debuggers and interpreters Program loading and execugon Absolute loaders, relocatable loaders, linkage editors, and overlayloaders, debugging systems for higher-level and machine language CommunicaGons - Provide the mechanism for crea+ng virtual connec+ons among processes, users, and computer systems Allow users to send messages to one another s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another CSE Opera+ng System Principles 28 14

15 Policy vs. Mechanism Policy is what will be done? Which process runs next? The process used inaccessible memory (NULL), what do we do? Mechanism is how we implement policy An extendable scheduler The process is killed and memory core dumped. CSE Opera+ng System Principles 29 OS Implementa+ons Modern kernels are programmed in C Hardware details are abstracted away CPU specific instruc+ons needed for normal OS tasks, e.g. seqng the +mer interrupt, are wrijen in assembly CSE Opera+ng System Principles 30 15

16 Opera+ng System Structure All opera+ng systems have some structure which usually dictates the flexibility and robustness of the sogware Separa+on of components: Drivers Scheduler Process Management File system Organiza+on of components can have huge impact on the usability of the OS, from a user and system standpoint! CSE Opera+ng System Principles 31 MSDOS Not well modularized, wrijen to take lijle space. CSE Opera+ng System Principles 32 16

17 Layered Approach (UNIX) CSE Opera+ng System Principles 33 Layered System Origin of the term shell and kernel. Many challenges: Clean separa+on of layers, no viola+ons ( cross layer boundaries inappropriately ) Speed! Iden+fying layers CPU scheduling vs. Memory Management CSE Opera+ng System Principles 34 17

18 Android Structure CSE Opera+ng System Principles 35 Extreme Approach: Microkernels CSE Opera+ng System Principles 36 18

19 Microkernels Moves as much from the kernel into user space Communica+on takes place between user modules using message passing Benefits: Easier to extend a microkernel Easier to port the opera+ng system to new architectures More reliable (less code is running in kernel mode) More secure Detriments: Performance overhead of user space to kernel space communica+on CSE Opera+ng System Principles 37 Mac OS graphical user interface Aqua application environments and services Java Cocoa Quicktime BSD kernel environment BSD Mach I/O kit kernel extensions CSE Opera+ng System Principles 38 19

20 Plug and Play: Kernel Modules Modern opera+ng systems must be flexible enough to change/add/remove behavior on the fly. Examples: Scheduling classes File systems Loadable system calls (uncommon) Executable formats Drivers (most common) CSE Opera+ng System Principles 39 CSE Opera+ng System Principles 40 20

21 $ /sbin/lsmod Module `lsmod` Size Used by openafs autofs sunrpc q bnx2fc cnic CSE Opera+ng System Principles 41 Virtual Machines A layered system structural model which is capable of running a kernel as a regular user program, trea+ng the actual hardware and underlying OS as virtual hardware CPU and memory access is iden+cal Host opera+ng system allocates and manages hardware used by virtual machine CSE Opera+ng System Principles 42 21

22 Virtual Machines (a) Regular Machine (b) Virtualized Machine CSE Opera+ng System Principles 43 Why have VMs? Efficient use of hardware resources Commercial benefits: Expand customer base Cut costs (consumer and business) Research benefits: Rapid deployment of kernels for tes+ng Honeypots and security tes+ng Infrastructure modulariza+on One VM dedicated to a single task (DNS, HTTP, etc.) CSE Opera+ng System Principles 44 22

23 Recap Key Points: Services an OS provides System calls System programs OS Design Goals and implementa+on OS structure Virtual Machines CSE Opera+ng System Principles 45 23