Chap_10Lesson07Emsys3EbhuhuFileSysOrg.pdf

book "Embedded Systems - Architecture, Programming and Design" by Raj Kamal

1. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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REAL TIME OPERATING SYSTEMS

Lesson-7:
File System Organization and
Implementation

2. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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1. File

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Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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File
a named entity on a magnetic disc, or
optical disc, or system memory or memory
stick
contains has the data, characters and text

4. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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i) A file 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’ or
simply ,simply, as a ‘file’ itself (virtual
device).
OSes differing abstractions of a file

5. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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(iii) May be an unstructured record of bits
or bytes.
(iv) A file device may be a pipe -like device


OSes differing abstractions of a file

6. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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2. 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 system

8. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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Standard 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 interfaces
must.
Then only then can systems can be portable.

9. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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Two type of file systems─ Block File
System
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.

10. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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Two type of file systems ─ Byte Stream File
System
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 N
bytes

11. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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POSIX
A standard set of interfaces.
File operations are as the operations on a
linear sequence of bytes

12. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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POSIX
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 & T
UNIX System V Interface.

13. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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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 the POSIX
File System

14. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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UNIX and LINUX File Systems
Unix has a structured file system with an
unstructured hardware interface.
Linux supports different standard file-
systems for the system

15. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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File Device
File devices block devices in UNIX.
Linux  permits the use of a block devices
as a char devices also
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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Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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RAM 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 and
then subfolder. There is hierarchical tree
like filing organisation

17. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
Raj Kamal, Publs.: McGraw-Hill Education
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3. File descriptor

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File descriptor─ fd
An integer, which returns on opening a file
and which points to a data structure.

19. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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Data structure for File describing
Identity
Creator or Owner
State
Locks and Protection fields
file Info
Sharing Permission
Count
Storing Media Details

20. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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Summary

21. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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We learnt
•File Manager has functions to create, open,
reads, seek a record, write, and close a file.
•A file has a file descriptor.

22. 2015
Chapter-10 L7: "Embedded Systems - Architecture, Programming and Design" ,
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End of Lesson 7 of Chapter 10