1. Christo Wilson Project 4: File System in Pintos
8/22/2012
CS 5600 Computer Systems
Project 4: File System in Pintos
Defense

2. File System in Pintos Pintos already implements a basic file system
Can create fixed size files in a single root directory
But this system has limitations
No support for nested directories
No support for files that grow in size
No caching or preemptive reading

3. Your Goals Implement indexed files Implement nested directories
Files should begin life as a single sector and grow dynamically as necessary
Processes should be able to seek and write past the end of a file
Requires heavily modifying Pintos’ inodes
Implement nested directories
You will need to implement new system calls to manipulate directories
chdir(), mkdir(), readdir(), isdir()
Inode management: inumber()  get the inode of a file or directory

4. Your Goals (cont.) Implement a buffer cache
Up to 64 sectors of disk data should be buffered in RAM
Implement a write-back cache
Cache must be periodically flushed to disk
How to handle eviction?
Carefully synchronize file operations
Accesses to independent files/directories should not block each other
Concurrent reading/writing of a single file needs to be handled carefully

5. What Pintos Does For You
Basic disk management
Read/write access to sectors
Basic management of free space
You’ve already implemented file descriptors and most of the file system API ;)

6. Inodes in Pintos filesys/inode.c /* On-disk inode.
Must be exactly BLOCK_SECTOR_SIZE bytes long. */
struct inode_disk {
block_sector_t start; /* First data sector. */
off_t length; /* File size in bytes. */
unsigned magic; /* Magic number. */
uint32_t unused[125]; /* Not used. */ };

7. Directories in Pintos filesys/directory.c
Implements a single root directory
i.e. no subdirectories
Must be overhauled to allow a directory to contain other directories
e.g. subdirectories

8. Key Challenges Choosing the right data structures
How do you encode directory and file information on disk?
How do you keep track of the locations of dynamically allocated file blocks
Properly managing your cache
Implementing performant cache eviction is tricky
Write-back cache must be periodically flushed
Implementing correct and performant synchronization

9. More Key Challenges
Each process needs to have an associated working directory
Necessary for resolving relative file accesses
E.g. open(“../file.txt”) or open(“./my_thing”)
Used by the pwd program

10. Modified Files filesys/Make.vars 6 filesys/cache.c 473 # new file!
filesys/cache.h 23 # new file!
filesys/directory.c 99
filesys/directory.h 3
filesys/file.c 4
filesys/filesys.c 194
filesys/filesys.h 5
filesys/free-map.c 45
filesys/free-map.h 4
filesys/fsutil.c 8
filesys/inode.c 444
filesys/inode.h 11
userprog/process.c 12
userprog/syscall.c 37
15+ files changed, 1368 insertions(+), 286 deletions(-)

11. This Project Is the Biggest
The reference solution for Project 4 includes way more lines of code than any other project thus far
Start early!

12. Extra Credit! Project 4 can built on top of Project 2 or Project 3
If you build on top of Project 3, you get 2 extra credit points!
This requires having a rock-solid VM implementation

13. Grading 15 (+2) points total To receive full credit:
Turn in working, well documented code that compiles successfully and completes all tests (50%)
Turn in a complete, well thought our design document (50%)
If your code doesn’t compile or doesn’t run, you get zero credit
Must run on the CCIS Linux machines!
All code will be scanned by plagiarism detection software

14. Turning In Your Project
Register yourself for the grading system
$ /course/cs5600f14/bin/register-student [NUID]
Register your group
All group members must run the script!
$ /course/cs5600f14/bin/register project4 [team name]
Run the turn-in script
Two parameters: project name and code directory
$ /course/cs5600f14/bin/turnin project4 ~/pintos/src/

15. DUE: December 3
11:59:59PM EST
Questions?