1. Project 4. “File System Implementation”
Dong Jin Kim,
PhD student

2. Introduction to Projects
Project 1: Setting up Environment for Project
Project 2: Linux Fundamental
Project 3: System Call and Synchronization
Project 4: File System
Project 5: Device Driver for Embedded H/W
Especially, including “BeagleBoard Development”

3. Contents of Project 4
Task 1. Data encryption on FUSE file system (30%)
Task 2. Buffer cache implementation on FUSE file system (30%)
Task 3. File system performance evaluation (10%)
Report (30%)
Explanation about your work
Answer to questions

4. FUSE File System What is FUSE?
FUSE : File System in User space
General File System is in the Kernel Space
Our Goal
Simple Buffer Cache Management in FUSE

5. FUSE Install
Download provided “fuse tar.gz” from the course home page
# wget
# tar xf fuse tar.gz
# cd fuse-2.9.4
# ./configure
# make
# make install

6. FUSE Tools
# wget
# tar xf fuse-tutorial.
# cd fuse-tutorial
# ./configure
# make

7. Use FUSE File System # cd src # mkdir /mnt/fuse # mkdir /root/fuse
# ./bbfs -o direct_io /mnt/fuse /root/fuse
# mount
Check information
Mounting Point
Real Dir.

8. General File System File system operation in kernel space User Program
read()
write()
User Space
Kernel Space
VFS
File System

9. Current FUSE File System
File system operation in user space
FUSE
bb_read
bb_write
User Program
read()
write()
read()
write()
User Space
System Call
Kernel Space
VFS
File System

10. Data Encryption Encrypt data using “keys” FUSE User Program read()
Task 1
Data Encryption
Encrypt data using “keys”
FUSE
bb_read
bb_write
User Program
Encrypted data
read()
write()
read()
write()
User Space
System Call
Kernel Space
VFS
File System

11. Simple Encryption and Decryption Method
Task 1
Simple Encryption and Decryption Method
Using encryption, only users with correct keys can take correct data
Incorrect keys will give incorrect data
For each “char” or “byte”, encrypt with …
Addition: add a value to original data
Right shift: after addition, an amount of bit-shift operation to the data
Decryption = reverse of encryption 1 1
2-bit right shift

12. Modify FUSE for Encryption and Decryption
Task 1
Modify FUSE for Encryption and Decryption
Modify 2 functions in bbfs.c
bb_read
Decrypt after pread called
bb_write
Encrypt before pwrite called
With correct keys, correct data should be available
With incorrect keys, correct data should not be available
How to give encryption keys
Create “fuse-tutorial /src/ee516.conf” file
First line: two non-negative integer, separated by space or tab(\t)
First integer: key for addition
The number that should be added to original data
Second integer: key for shift
The number of bit-shifts for each byte
When you mount fuse file system, read this file and take keys
If you want to change keys, unmount fuse  modify ee516.conf file  mount fuse

13. Example Result File written in (addition, shift) = (3, 5)
Task 1
Example Result
File written in (addition, shift) = (3, 5)
Read with (4, 5), (3, 4), and (4, 4), respectively

14. Buffer Cache Implementation
Task 2
Buffer Cache Implementation
Add buffer cache
Add this
FUSE
bb_read
bb_write
Buffer Cache
User Program
read()
write()
read()
write()
User Space
System Call
Kernel Space
VFS
File System

15. Modify FUSE for Buffer Cache Implementation
Task 2
Modify FUSE for Buffer Cache Implementation
Modify 3 functions in bbfs.c
bb_read
bb_write
bb_release
Read and write operations
Read
Buffer hit
Return contents
Buffer miss
If buffer is full, evict some contents
Read from disk and write to buffer
Write
Write into the buffer
Release
If there are dirty data of corresponding file in the buffer, write them to the disk

16. Eviction Algorithms to Implement
Task 2
Eviction Algorithms to Implement
Implement 2 eviction algorithms
1. Random eviction
Choose victim randomly
2. LRU
Least Recently Used
For buffer hit, entry moves to the head of the queue

17. Specification to Implement the Buffer Cache
Task 2
Specification to Implement the Buffer Cache
Do not use O_DIRECT flags for testing the given FUSE file system
FUSE doesn’t support O_DIRECT yet
“Buffer Cache” should have an array of “chunks” and a linked list
Each “chunk” stores 4KB data
You can assume that request size is fixed to 4KB
The linked list will manage eviction algorithm
Buffer Cache
Buffer Cache Size : 5MB
Don’t care about consistency (for just 1 user)
Eviction policy will given as an integer in the second line of “ee516.conf” file
0: no buffer / 1: random eviction / 2: LRU

18. Performance Evaluation
Task 3
Performance Evaluation
Use benchmark tool of project 1
Remove all O_DIRECT flags for FUSE
Use FILESIZE 10MB
Use request size (second parameter of execution) 4096
You can use
Run benchmark and analyze
Current Linux file system
Same as project 1
FUSE with
0. No encryption and no buffer
1. No encryption and random eviction buffer
2. No encryption and LRU buffer
3. Encryption and no buffer
4. Encryption and random eviction buffer
5. Encryption and LRU buffer

19. Questions for the Report
Find answers from your brain, web site, book,
Q1. Pros. and Cons. of FUSE file system (against file system in kernel space)
Q2. In our encryption, can different key pairs give same encrypted / decrypted data? Why?
Q3. List several encryption methods and analyze them.
Q4. Why performances of Linux and FUSE file systems are different?
Q5. Why performances of different eviction algorithms are different? In which cases each eviction algorithm can have advantage?
Specify the references

20. Submission Contents Submission Source codes Report
Implemented and modified codes
Include comments in the source codes
Report
Key points of your source code
Do not attach entire source codes in the report
Result screenshots
Answers of questions
Submission
Due date: Nov. 28., PM 23:59
Delay penalty
10% per day (AM 00:00)
Joo Kyung Ro
Title: [EE516 Project 4] student_number
Attached file: student_number.zip
Various compression format is allowed