Chapter 10: File-System Interface File Concept File Structure File ...

File Concept Contiguous logical address space Types: z

Data numeric

Chapter 10: FileFile-System Interface

character binary z

Program

Operating System Concepts – 7th Edition, Jan 1, 2005

File Structure

10.2

Silberschatz, Galvin and Gagne ©2005

File Attributes

None - sequence of words, bytes

Name – only information kept in human-readable form

Simple record structure

Identifier – unique tag (number) identifies file within file system

z

Lines

Type – needed for systems that support different types

z

Fixed length

Location – pointer to file location on device

z

Variable length

Size – current file size

Complex Structures z

Formatted document

z

Relocatable load file

Protection – controls who can do reading, writing, executing Time, date, and user identification – data for protection, security,

and usage monitoring

Can simulate last two with first method by inserting appropriate

control characters

Information about files are kept in the directory structure, which is

maintained on the disk

Who decides: z

Operating system

z

Program


10.3



File Operations

10.4


Open Files Several pieces of data are needed to manage open files:

File is an abstract data type Create

z

File pointer: pointer to last read/write location, per process that has the file open

z

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

Delete

z

Disk location of the file: cache of data access information

Truncate

z

Access rights: per-process access mode information

Write Read Reposition within file

Open(Fi) – search the directory structure on disk for entry Fi, and

move the content of entry to memory Close (Fi) – move the content of entry Fi in memory to directory

structure on disk


10.5



10.6


1

File Types – Name, Extension

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


10.7


SequentialSequential-access File


10.9


A Typical FileFile-system Organization


10.8


Example of Index and Relative Files


10.10


Operations Performed on Directory Search for a file Create a file Delete a file List a directory Rename a file Traverse the file system


10.11



10.12


2

SingleSingle-Level Directory

TwoTwo-Level Directory Separate directory for each user

A single directory for all users

Naming problem Path name

Grouping problem

Can have the same file name for different user Efficient searching No grouping capability


10.13


TreeTree-Structured Directories


10.14


TreeTree-Structured Directories (Cont) Efficient searching Grouping Capability Current directory (working directory)


10.15


TreeTree-Structured Directories (Cont)

z

cd /spell/mail/prog

z

type list


10.16


AcyclicAcyclic-Graph Directories Have shared subdirectories and files

Absolute or relative path name Creating a new file is done in current directory Delete a file

rm Creating a new subdirectory is done in current directory

mkdir Example: if in current directory /mail mkdir count

mail prog

copy prt exp count

Deleting “mail” ⇒ deleting the entire subtree rooted by “mail” Operating System Concepts – 7th Edition, Jan 1, 2005

10.17



10.18


3

General Graph Directory

File System Mounting A file system must be mounted before it can be

accessed A unmounted file system (i.e. Fig. 11-11(b)) is

mounted at a mount point


10.19



(a) Existing. (b) Unmounted Partition


10.21


Mount Point


Protection what can be done

z

by whom

Mode of access: read, write, execute

Three classes of users

Types of access z

Read

z

Write

z

Execute

z

Append

z

Delete

z

List


10.22

Access Lists and Groups

File owner/creator should be able to control: z


10.20

a) owner access

7

⇒

b) group access

6

⇒

c) public access

1

⇒

RWX 111 RWX 110 RWX 001

Ask manager to create a group (unique name), say G, and add some users to the group.

For a particular file (say game) or subdirectory, define an appropriate access.

owner chmod

group

public

761

game

Attach a group to a file chgrp Operating System Concepts –

7th

Edition, Jan 1, 2005

10.23


Operating System Concepts –

7th

Edition, Jan 1, 2005

G

game

10.24


4

Windows XP AccessAccess-control List Management


10.25


A Sample UNIX Directory Listing


10.26


End of Chapter 10

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