file system organization and implementation

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2008 Chapter-8 L7: "Embedded Systems - Architecture, Programming

and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.1

REAL TIME OPERATING SYSTEMS

Lesson-7:

File System Organization and

Implementation


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1. File1. File


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FileFile

a named entity on a magnetic disc, or

optical disc, or system memory or

memory stick

contains has the data, characters and text


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i) Afile may be a named entity that is a

structured record named entity as on a disk,

which has having random access in the

system.

ii) May be a structured record on a RAM

analogous to a disk and may also be either

called separately called as RAM disk orsimply ,simply, as a file itself (virtual

device).

OSes differing abstractions of a fileOSes differing abstractions of a file


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(iii) May be an unstructured record of bits

or bytes.

(iv) Afile device may be a pipe -like device

OSes differing abstractions of a fileOSes differing abstractions of a file


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2. File organization in a file system2. File organization in a file system


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File is organized in a way according to a file

system, which has set of command

functions for operations on the file

File organization in a systemFile organization in a system


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and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

8

Standard set of interfacesStandard set of interfaces

Should a file having integers differ from a

file having bytes?

Should a file having bytes differ from file

having characters?

Due to the differing approaches to device

and file management interfaces, the

development of a set of standard interfacesmust.

Then only then can systems can be portable.


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9

Two type of file systemsTwo type of file systemsBlock FileBlock File

SystemSystem

Block File System. Its application generates

records to be saved into the memory.

First structured into a suitable format and

then translated into block-streams.

A file pointer (record) points to a block

from the start to the end of the file.


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Two type of file systemsTwo type of file systemsByte Stream FileByte Stream File

SystemSystem

Byte Stream File-System. Its application

generates record stream.

Stream are to be saved into the memory.

These are first structured into a suitable

format and then translated into byte-stream.

A file pointer (byte index) points to a byte

from the start index = 0 to N-1 in a file of Nbytes


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POSIXPOSIX

A standard set of interfaces.

File operations are as the operations on a

linear sequence of bytes


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POSIXPOSIX

POSIX stands for Portable Operating

System Interface IEEE standard for coding

the programs when using the multiple

threads.

The X after I is because of the interfaces

being similar to ones in UNIX like.

It is according to the definitions at A T & TUNIX System V Interface.


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open ( )

write ( ) in the byte stream at the present

pointer position

read ( ) from the byte stream present pointer

position

lseek (List seek) or set the file pointer in the

byte stream

fcntl ( )

close ( )

Set of Command Functions in theSet of Command Functions in the

POSIX File SystemPOSIX File System


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UNIX and LINUX File SystemsUNIX and LINUX File Systems

Unix has a structured file system with an

unstructured hardware interface.

Linux supports different standard file-

systems for the system


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File DeviceFile Device

File devices are block devices in UNIX.

Linux permits the use of a block devices as

a char devices also. This is because between

block-device to char-device, Linux has an

additional interface.

Kernel interface is identical for the char and

block devices in Linux and not in UNIX.


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RAM diskRAM disk

File on the RAM that is hierarchically

organized is is known as RAM disk.

RAM memory storage is analogous to that

on the disk and accessing is also analogous

to a disk.

For example, path for accessing a file is

directory, then subdirectory, then folder andthen subfolder. There is hierarchical tree

like filing organisation


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3. File descriptor3. File descriptor


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File descriptorFile descriptor fd fd

An integer, which returns on opening a file

and which points to a data structure.


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File describing data structureFile describing data structure

Identity

Creator or Owner

State

Locks and Protection fields

file Info

Sharing Permission

Count

Storing Media Details


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SummarySummary


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We learntWe learnt

File Manager has functions to create, open,reads, seek a record, write, and close a file.

A file has a file descriptor.


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End of Lesson 7 of Chapter 8End of Lesson 7 of Chapter 8

file system organization and implementation

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