东南大学操作系统课件(汪芸老师版)

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OS Design and Implementation(1)
• Important principle to separate Policy: What will be done? from Mechanism: How to do it?
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Simple Structure(2)
• MS-DOS – written to provide the most functionality in the least space
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System Calls
• Programming interface to the services provided by the OS • Typically written in a high-level language (C or C++)
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Example of System Calls
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OS Design and Implementation
• User goals and System goals
-- User goals : convenient to use, easy to learn, reliable, safe, and fast -- System : easy to design, implement, and maintain, as well as flexible, reliable, errorfree, and efficient
Chapter 2: Operating-System Structures
Services supported by Operating Systems
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Operating System Services
User interface Program execution - to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error) I/O operations File-system manipulation Communications Error detection
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MS-DOS execution
(a) At system startup (b) running a program
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FreeBSD Running Multiple Programs
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Dtrace in Solaris 10
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System Programs • System programs provide a convenient environment for program development and execution. They can be divided into:
– – – – – – – File manipulation Status information File modification Programming language support Program loading and execution Communications Application programs
– Not divided into modules – Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated
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MS-DOS Layer Structure
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Standard C Library Example • C program invoking printf() library call, which calls write() system call
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System Call Parameter Passing
• Three general methods used to pass parameters to the OS
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Layered Operating System
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UNIX System Structure
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Modules(4)
• Most modern operating systems
– 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
• Similar to layers but with more flexible
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Solaris Modular Approach
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Mac OS X Structure
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Microkernel System Structure(5)
• Moves as much from the kernel into “user” space • Communication takes place between user modules using message passing
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Operating System Structures
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OS Design and Implementation
• Internal structure of different Operating Systems can vary widely • Start by defining goals and specifications • Affected by choice of hardware, type of system
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Virtual Machines
• The resources of the physical computer are shared to create the virtual machines
– CPU scheduling can create the appearance that users have their own processor – Spooling and a file system can provide virtual card readers and virtual line printers – A normal user time-sharing terminal serves as the virtual machine operator’s console
-- Simplest: pass the parameters in registers -- Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register -- Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system
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Example of Standard API
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System Call Implementation
• Typically, a number associated with each system call
– System-call interface maintains a table indexed according to these numbers
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Parameter Passing via Table
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Types of System Calls
• • • • •
Process control File management Device management Information maintenance Communications
• Detriments:
– Performance overhead of user space to kernel space communication
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Virtual Machines • Layered approach to its logical conclusion • Identical interface to the underlying bare hardware • Each process executes on its own processor with its own (virtual) memory
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Microkernel System Structure • Benefits:
– Easier to extend a microkernel – Easier to port the operating system to new architectures – More reliable (less code is running in kernel mode) – More secure
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Operating System Services
• Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing – Resource allocation – Accounting - To keep track of which users use how much and what kinds of computer resources – Protection and security
• The system call interface invokes intended system call in OS kernel and returns status of the system call and any return values
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API /System Call /OS Relationship
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System Call Implementation
• The caller need know nothing about how the system call is implemented
– Just needs to obey API and understand what OS will do as a result call – Most details of OS interface hidden from programmer by API
• System call sequence to copy the contents of one file to another file
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System Calls • Mostly accessed by programs via a highlevel Application Program Interface (API) rather than direct system call use • Three most common APIs -- Win32 API for Windows -- POSIX API for POSIX-based systems -- Java API for the Java virtual machine (JVM)
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Layered Approach(3)
• 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. • Use functions (operations) and services of lower-level layers