ch10 操作系统

Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.6
Silberschatz, Galvin and Gagne ©2007
文件系统（ 文件系统（File Systems） ）
文件系统软件结构
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.9
Silberschatz, Galvin and Gagne ©2007
File Attributes
Name – only information kept in human-readable form 有些OS区分大小写（如Linux，Unix），有些不区分 （如DOS, Windows） Identifier – unique tag (number) identifies file within file system Type – needed for systems that support different types Location – pointer to file location on device Size – current file size Protection – controls who can do reading, writing, executing Time, date, and user identification – data for protection, security, and usage monitoring Information about files are kept in the directory structure, which is maintained on the disk
Chapter 10: File-System Interface
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
Silberschatz, Galvin and Gagne ©2007
Chapter 10: File-System Interface
Operating System Concepts with Java – 7th Edition, Nov 15, 2006 10.4 Silberschatz, Galvin and Gagne ©2007
File Concept
Contiguous logical address space Types: Data numeric character binary Program
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.13
Silberschatz, Galvin and Gagne ©2007
File import java.io.*; import java.nio.channels.*; public class LockingExample { public static final boolean EXCLUSIVE = false; public static final boolean SHARED = true; public static void main(String arsg[]) throws IOException { FileLock sharedLock = null; FileLock exclusiveLock = null; try { RandomAccessFile raf = new RandomAccessFile("file.txt", "rw"); // get the channel for the file FileChannel ch = raf.getChannel(); // this locks the first half of the file - exclusive exclusiveLock = ch.lock(0, raf.length()/2, EXCLUSIVE); /** Now modify the data . . . */ // release the lock exclusiveLock.release();
10.2
Silberschatz, Galvin and Gagne ©2007
Objectives
To explain the function of file systems To describe the interfaces to file systems To discuss file-system design tradeoffs, including access methods, file sharing, file locking, and directory structures To explore file-system protection
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.3
Silberschatz, Galvin and Gagne ©2007
File Concept
所有的计算机应用程序都要：存储信息、检索信息。 三个基本要求： 能够存储大量的信息（程序的输入/输出） 长期保存信息 可以共享（并发存取）信息 解决方法：把信息以一种单元，即文件的形式存储在 磁盘或其他外部介质上 文件是通过操作系统来管理的，包括文件的结构、命 名、存取、使用、保护和实现方法等——文件(管理) 系统
10.7
Silberschatz, Galvin and Gagne ©2007
文件管理要素（重点） 文件管理要素（重点）
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.8
Silberschatz, Galvin and Gagne ©2007
File Structure
None - sequence of words, bytes Simple record structure Lines Fixed length Variable length Complex Structures Formatted document Relocatable load file Can simulate last two with first method by inserting appropriate control characters Who decides: Operating system Program
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.5
Silberschatz, Galvin and Gagne ©2007
文件（ 文件（Files） ）
文件相关术语 域（Field）：基本数据单元 记录（Record）：一组相关的域 文件（File）：相似记录的集合 数据库（Database）：相关数据的集合 文件：一组带标识（称文件名）的在逻辑上有完整意义的信息项的序列 信息项：构成文件内容的基本单位 信息项长度：单个字节，或多个字节 文件内容的意义：由文件的建立者和使用者解释
File Concept Access Methods Directory Structure File-System Mounting File Sharing Protection
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.11
Silberschatz, Galvin and Gagne ©2007
Open Files
Several pieces of data are needed to manage open files: File pointer: pointer to last read/write location, per process that has the file open File-open count: counter of number of times a file is open – to allow removal of data from open-file table when last processes closes it Disk location of the file: cache of data access information Access rights: per-process access mode information
Operating System Concepts with Java – 7th Edition, Nov 15, 2006
10.12
Silberschatz, Galvin and Gagne ©2007
Open File Locking
Provided by some operating systems and file systems Mediates access to a file Mandatory or advisory: Mandatory – access is denied depending on locks held and requested Advisory – processes can find status of locks and decide what to do