Module 6.1 Operating Systems

File Concept

Contiguous logical address space

• Data

  • Numeric

  • Character

  • Binary

• Program

Enumerate the types of File Concept

Name

only information kept in human-readable form

Identifier

unique tag (number) identifies the file within the file system

Type

needed for systems that support different types

Location

pointer to file location on the device

Size

current file size

Protection

controls who can do the reading, writing, executing

Time, date, and user identification

data for protection, security, and usage monitoring

Directory Structure

Information about files are kept in the ____

Directory Structure

A collection of nodes containing information about all files

DISK

Both the directory structure and the files reside on

• Create

• Write

• Read

• Reposition within file

• Delete

• Truncate

• Open (Fi)

• Close (Fi)

Enumerate File Operations

Open Files

Several pieces of data are needed to manage open files:

Open-file table

tracks 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

Open File Locking

Provided by some operating systems and file systems

Shared lock

It is similar to reader lock

Shared lock

several processes can acquire concurrently

Mandatory

access is denied depending on locks held and requested

Advisory

processes can find status of locks and decide what to do

Executable Files - ex, co, bin`

Ready-to-run machine-language program.

Object Files - obj

Compiled, machine language, not linked

Source Code Files

ource code in various languages

Batch Files

Commands to the command interpreter

Text Files

Textual data, documents.

Word Processor Files

Various word-processor formats

Library Files

Libraries of routines for programmers

Print or View Files

ASCII or binary file in a format for printing or viewing.

Archive Files

Related files grouped into one file, sometimes compressed, for archiving or storage

Multimedia Files

Binary file containing audio or A/V information.

None

sequence of words, bytes

• Lines

• Fixed length

• Variable length

Enumerate Simple record structure

• Formatted document

• Relocatable load file

Enumerate Complex Structures

• Sequential Access

• Direct Access

Types of Access Methods

• read next

• write next

• Reset

• no read after last write (rewrite)

Enumerate the Operations of Sequential Access

Direct Access

A file is fixed length logical records

• read n

• write n

• position to n

  • read next

  • write next

  • rewrite n

Enumerate operation of Direct Access

Relative block numbers

allow OS to decide where file should be placed

Partitions

Disk can be subdivided into ___

RAID

Disks or partitions can be ____ protected against failure

raw and formatted

Disk or partition can be used _____ without a file system, or _____ with a file system

minidisks, slices

Partitions also known as

volume

Entity containing file system

device directory or volume table of contents

volume containing a file system also tracks that file system’s info

tmpfs

memory-based volatile FS for fast, temporary I/O

objfs

interface into kernel memory to get kernel symbols for debugging

ctfs

contract file system for managing daemons

lofs

loopback file system allows one FS to be accessed in place of another

procfs

kernel interface to process structures

ufs, zfs

general purpose file systems

• Efficiency

• Naming

• Grouping

The directory is organized logically to obtain?

Acyclic-Graph Directories

have shared subdirectories and files

Link

another name (pointer) to an existing file

Resolve the link

follow pointer to locate the file

Garbage collection

How do we guarantee no cycles

True

True or False

A file system must be mounted before it can be accessed

File Sharing

• Sharing of files on multi-user systems is desirable

• Sharing may be done through a protection scheme

• On distributed systems, files may be shared across a network

Network File System (NFS)

common distributed file-sharing method

User IDs

identify users, allowing permissions and protections to be per-user

Group IDs

allow users to be in groups, permitting group access rights

File Sharing – Remote File Systems

Uses networking to allow file system access between systems

Client-server model

allows clients to mount remote file systems from servers

NFS

standard UNIX client-server file sharing protocol

CIFS

standard Windows protocol

True

True or false:

All file systems have failure modes

metadata

corruption of directory structures or other non-user data,

state information

Recovery from failure can involve _______ about status of each remote request

Stateless protocols (NFS v3)

include all information in each request, allowing easy recovery but less security

File Sharing – Consistency Semantics

Specify how multiple users are to access a shared file simultaneously

Andrew File System (AFS)

implemented complex remote file sharing semantics

Unix file system (UFS)

Writes to an open file visible immediately to other users of the same open file and shares file pointer to allow multiple users to read and write concurrently