Chapter 10: File-System Interface

Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition,

Chapter 10: File-System Interface

• File Concept
• Access Methods
• Directory Structure

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

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

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

File Concept

• Contiguous logical address space�
• Types:
• Data
• numeric
• character
• binary
• Program

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

File Structure

• None - sequence of words, bytes
• Simple record structure
• Lines
• Fixed length
• Variable length
• Complex Structures
• Formatted document
• Relocatable load file

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

File Attributes

• Name – only information kept in human-readable form
• 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

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

File Operations

• File is an abstract data type
• Create
• Write
• Read
• Reposition within file
• Delete
• Truncate
• Open(F_i) – search the directory structure on disk for entry F_i, and move the content of entry to memory
• Close (F_i) – move the content of entry F_i in memory to directory structure on disk

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

File Types – Name, Extension

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

Access Methods

• Sequential Access

read next

write next

reset

no read after last write

(rewrite)

• Direct Access

read n

write n

position to n

read next

write next

rewrite n

n = relative block number

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

Sequential-access File

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

Simulation of Sequential Access on Direct-access File

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

Directory Structure

• A collection of nodes containing information about all files

F 1

F 2

F 3

F 4

F n

Directory

Files

Both the directory structure and the files reside on disk

Backups of these two structures are kept on tapes

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

Operations Performed on Directory

• Search for a file
• Create a file
• Delete a file
• List a directory
• Rename a file
• Traverse the file system

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Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition

End of Chapter 10

Silberschatz, Galvin and Gagne ©2009

Operating System Concepts – 8^th Edition,