1 Chapter 12 File Management Patricia Roy Manatee Community College, Venice, FL ©2008, Prentice...
-
Upload
thomas-greene -
Category
Documents
-
view
219 -
download
2
Transcript of 1 Chapter 12 File Management Patricia Roy Manatee Community College, Venice, FL ©2008, Prentice...
1
Chapter 12File Management
Patricia RoyManatee Community College, Venice,
FL©2008, Prentice Hall
Operating Systems:Internals and Design Principles, 6/E
William Stallings
2
File Management
• File management system consists of system utility programs that run as privileged applications
• Concerned with secondary storage
• Long-term existence
• Shared between processes
• Structure (internal or directories)
3
File Attributes
Possible file attributes
4
File System Calls
• Principle Win32 API functions for file I/O
• Second column gives nearest UNIX equivalent
5
Files System Software Architecture
6
Elements of File Management
7
File Management Functions
• Identify and locate a selected file
• Use a directory to describe the location of all files plus their attributes
• On a shared system describe user access control
8
Criteria for File Organization
• Quick random access– Needed when accessing a single record
• Ease of update
• Economy of storage– Should be minimum redundancy in the data– Redundancy can be used to speed access such as
an index
• Simple maintenance
• Reliability
9
The Pile
10
The Sequential File
11
Indexed Sequential File
12
Indexed File
13
File Organization
• The Direct or Hashed File– Directly access a block at a known address– Key field required for each record
14
Performance
15
File Directories
• Contains information about files– Attributes– Location– Ownership
• Directory itself is a file owned by the operating system
• Provides mapping between file names and the files themselves
16
Information Elements of a File Directory
17
Information Elements of a File Directory
18
Hierarchical, or Tree-Structured Directory
• Master directory with user directories underneath it
• Each user directory may have subdirectories and files as entries
19
Tree-Structured Directory
20
Example of Tree-Structured Directory
21
Hierarchical, or Tree-Structured Directory
• Files can be located by following a path from the root, or master, directory down various branches– This is the pathname for the file
• Can have several files with the same file name as long as they have unique path names
• Current directory is the working directory
• Files are referenced relative to the working directory
22
Directory System Calls
• Principle Win32 API functions for directory management
• Second column gives nearest UNIX equivalent, when one exists
23
File Sharing
• In multiuser system, allow files to be shared among users
• Two issues– Access rights (read, write, execute)– Management of simultaneous access (cf.
interprocess communication, mutual exclusion)
24
Access Matrix
25
Access Control List
26
Capability Lists
27
File System Implementation
A possible file system layout
28
Secondary Storage Management
• Space must be allocated to files
• Must keep track of the space available for allocation
29
Disk Space Management
• Dark line (left hand scale) gives data rate of a disk• Dotted line (right hand scale) gives disk space efficiency• All files 2KB
Block size
30
Contiguous Allocation
• Single set of blocks is allocated to a file at the time of creation
• Only a single entry in the file allocation table– Starting block and length of the file
• External fragmentation will occur– Need to perform compaction
31
Contiguous File Allocation
32
Contiguous File Allocation
33
Chained Allocation
• Allocation on basis of individual block
• Each block contains a pointer to the next block in the chain
• Only single entry in the file allocation table– Starting block and length of file
34
Chained Allocation
• No external fragmentation
• Best for sequential files
• No accommodation of the principle of locality
35
Chained Allocation
36
Chained Allocation
37
Indexed Allocation
• File allocation table contains a separate one-level index for each file
• The index has one entry for each portion allocated to the file
• The file allocation table contains block number for the index
38
Indexed Allocation
39
The MS-DOS File System (1)
The MS-DOS directory entry
40
The MS-DOS File System (2)
• Maximum partition for different block sizes• The empty boxes represent forbidden combinations
41
Inodes
• Index node
• Control structure that contains key information for a particular file: attributes and location of blocks
42
FreeBSD
File
Allocation
43
UNIX Directories and Inodes
44
The UNIX File System
The steps in looking up /usr/ast/mbox
45
Shared Files (1)
File system containing a shared file
46
Shared Files (2)
(a) Situation prior to linking
(b) After the link is created
(c) After the original owner removes the file
47
Windows 2000 (1)
The NTFS master file table
48
Windows 2000 (2)
An MFT record for a three-run, nine-block file
49
Windows 2000 (3)
A file that requires three MFT records to store its runs
50
Linux Virtual File System
• Uniform file system interface to user processes
• Represents any conceivable file system’s general feature and behavior
• Assumes files are objects that share basic properties regardless of the target file system
51
Linux Virtual File System Context
52
Linux Virtual File System Concept