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Nội dung Text: Bài giảng Hệ điều hành nâng cao - Chapter 10: File - System Interface
- Chapter 10:
File-System Interface
Operating System Concepts – 8th Edition
Operating System Concepts – 8th Edition 10.1 Silberschatz, Galvin and Gagne ©2009
- Chapter 10: File-System Interface
s File Concept
s Access Methods
s Directory Structure
s File-System Mounting
s File Sharing
s Protection
Operating System Concepts – 8th Edition 10.2 Silberschatz, Galvin and Gagne ©2009
- Objectives
s To explain the function of file systems
s To describe the interfaces to file systems
s To discuss file-system design tradeoffs, including access methods, file
sharing, file locking, and directory structures
s To explore file-system protection
Operating System Concepts – 8th Edition 10.3 Silberschatz, Galvin and Gagne ©2009
- File Concept
s Contiguous logical address space
s Types:
q Data
4 numeric
4 character
4 binary
q Program
Operating System Concepts – 8th Edition 10.4 Silberschatz, Galvin and Gagne ©2009
- File Structure
s None - sequence of words, bytes
s Simple record structure
q
Lines
q Fixed length
q Variable length
s Complex Structures
q Formatted document
q Relocatable load file
s Can simulate last two with first method by inserting appropriate control
characters
s Who decides:
q Operating system
q Program
Operating System Concepts – 8th Edition 10.5 Silberschatz, Galvin and Gagne ©2009
- File Attributes
s Name – only information kept in human-readable form
s Identifier – unique tag (number) identifies file within file system
s Type – needed for systems that support different types
s Location – pointer to file location on device
s Size – current file size
s Protection – controls who can do reading, writing, executing
s Time, date, and user identification – data for protection, security, and
usage monitoring
s Information about files are kept in the directory structure, which is
maintained on the disk
Operating System Concepts – 8th Edition 10.6 Silberschatz, Galvin and Gagne ©2009
- File Operations
s File is an abstract data type
s Create
s Write
s Read
s Reposition within file
s Delete
s Truncate
s Open(Fi) – search the directory structure on disk for entry Fi, and move
the content of entry to memory
s Close (Fi) – move the content of entry Fi in memory to directory
structure on disk
Operating System Concepts – 8th Edition 10.7 Silberschatz, Galvin and Gagne ©2009
- Open Files
s Several pieces of data are needed to manage open files:
q File pointer: pointer to last read/write location, per process that has
the file open
q 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
q Disk location of the file: cache of data access information
q Access rights: per-process access mode information
Operating System Concepts – 8th Edition 10.8 Silberschatz, Galvin and Gagne ©2009
- Open File Locking
s Provided by some operating systems and file systems
s Mediates access to a file
s Mandatory or advisory:
q Mandatory – access is denied depending on locks held and
requested
q Advisory – processes can find status of locks and decide what to
do
Operating System Concepts – 8th Edition 10.9 Silberschatz, Galvin and Gagne ©2009
- File Locking Example – Java API
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();
Operating System Concepts – 8th Edition 10.10 Silberschatz, Galvin and Gagne ©2009
- File Locking Example –
Java API (Cont.)
// this locks the second half of the file - shared
sharedLock = ch.lock(raf.length()/2+1, raf.length(),
SHARED);
/** Now read the data . . . */
// release the lock
sharedLock.release();
} catch (java.io.IOException ioe) {
System.err.println(ioe);
}finally {
if (exclusiveLock != null)
exclusiveLock.release();
if (sharedLock != null)
sharedLock.release();
}
}
}
Operating System Concepts – 8th Edition 10.11 Silberschatz, Galvin and Gagne ©2009
- File Types – Name, Extension
Operating System Concepts – 8th Edition 10.12 Silberschatz, Galvin and Gagne ©2009
- Access Methods
s Sequential Access
read next
write next
reset
no read after last write
(rewrite)
s Direct Access
read n
write n
position to n
read next
write next
rewrite n
n = relative block number
Operating System Concepts – 8th Edition 10.13 Silberschatz, Galvin and Gagne ©2009
- Sequential-access File
Operating System Concepts – 8th Edition 10.14 Silberschatz, Galvin and Gagne ©2009
- Simulation of Sequential Access on
Direct-access File
Operating System Concepts – 8th Edition 10.15 Silberschatz, Galvin and Gagne ©2009
- Example of Index and Relative Files
Operating System Concepts – 8th Edition 10.16 Silberschatz, Galvin and Gagne ©2009
- Directory Structure
s A collection of nodes containing information about all files
Directory
Files
F1 F2 F4
F3
Fn
Both the directory structure and the files reside on disk
Backups of these two structures are kept on tapes
Operating System Concepts – 8th Edition 10.17 Silberschatz, Galvin and Gagne ©2009
- Disk Structure
s Disk can be subdivided into partitions
s Disks or partitions can be RAID protected against failure
s Disk or partition can be used raw – without a file system, or formatted
with a file system
s Partitions also known as minidisks, slices
s Entity containing file system known as a volume
s Each volume containing file system also tracks that file system’s info in
device directory or volume table of contents
s As well as general-purpose file systems there are many special-
purpose file systems, frequently all within the same operating system
or computer
Operating System Concepts – 8th Edition 10.18 Silberschatz, Galvin and Gagne ©2009
- A Typical File-system Organization
Operating System Concepts – 8th Edition 10.19 Silberschatz, Galvin and Gagne ©2009
- Operations Performed on Directory
s Search for a file
s Create a file
s Delete a file
s List a directory
s Rename a file
s Traverse the file system
Operating System Concepts – 8th Edition 10.20 Silberschatz, Galvin and Gagne ©2009
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