File System Design: Name Management and Protection in High Performance Computing, Slides of Computer Science

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High Performance Computing

Lecture 36

2 File System Design Issues

1. Disk management: efficient use of disk space

2. Name management: how users select files for

use

3. Protection: of files from users

4 Name Management: Directory

 Directory: mapping between file name and

file descriptor

 The OS could maintain a single directory for the

whole disk

 Problem: Need for unique name for files across all users  e.g., we could have only one file called program.c in the entire system

5 Name Management: Directory

 Directory: mapping between file name and

file descriptor

 The OS could maintain a single directory for the

whole disk

 The OS could maintain a separate directory for

each user

 My directory would be referred to when I try to access a file  Then each user could have a file called program.c  But only one file called README

7 Tree Structured Directory Hierarchy

 Tree: A kind of data structure

8 Tree Structured Directory Hierarchy

 Tree: A kind of data structure

node or vertex edge from parent node to child node the root node leaf nodes or leaves

10  Directories are stored on disk like regular files  Each contains (filename, index node) pairs  Each contains an entry with name. for itself  Special (nameless) directory called the root  Each file has a pathname that starts from the root directory  / separated sequence of directories Tree Structured Directory Hierarchy

11

Tree Structured Directory Hierarchy

root a (^) b c d e (^) f g^ h^ i j k l (^) m n o

a 78 b 85 c 100 /c/h/o

13 Protection

Objective: to prevent accidental or intentional

misuse of a file system

 Aspects of a protection mechanism

1. User identification (authentication)

 Establishing that the user is who he/she claims to be  Could be done using userid/password, and password verification on login  Passwords must be stored securely  There are other possibilities  Biometrics (fingerprints, iris recognition, etc)

14 Protection

Objective: to prevent accidental or intentional

misuse of a file system

 Aspects of a protection mechanism

1. User identification (authentication)

2. Authorization determination: determining what

the user is entitled to do to the file

 the system must keep track of what operations each user is allowed to do to each file  But that could be a huge amount of information

16 Protection

Objective: to prevent accidental or intentional

misuse of a file system

 Aspects of a protection mechanism

1. User identification (authentication)

2. Authorization determination: determining what

the user is entitled to do to the file

3. Access enforcement

• preventing users from doing unauthorized access