-- Lab 3: File Server: Reading, Writing and Sharing Files --

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Introduction

In this lab, you will continue to add functionality to YFS supporting SETATTR, OPEN, WRITE and READ operations.

Getting started

First, merge your solution to Lab 2 with the new code for Lab 3. There are no substantive differences in our code between the labs, except for a new tester. We have also provided stubs for the FUSE functions you need to implement in order to make your job easier. You can use the following commands to get the Lab 3 sources; see the directions for Lab 2 for more background on git.

% cd lab
% git commit -am 'my solution to lab2'
Created commit ...
% git pull
remote: Generating pack...
...
% git checkout -b lab3 origin/lab3
Branch lab3 set up to track remote branch refs/remotes/origin/lab3.
Switched to a new branch "lab3"
% git merge lab2

As before, if git reports any conflicts, edit the files to merge them manually, then run git commit -a. Lab 3 builds upon Lab 2 so make sure you pass the Lab 2 tester before proceeding. When you're done with Lab 3, you should be able to read and write files in your file system. For example, use the start.sh script to start up two separate yfs_clients with mountpoints at "./yfs1" and "./yfs2", which both use the same extent server for organizing its data:

% cd ~/lab
% ./start.sh

Then, you can write files to one directory and read them from the other:

% ls -l yfs1 yfs2
yfs1:
total 0

yfs2:
total 0
% echo "Hello world" > yfs1/hello.txt
% ls -l yfs1 yfs2
yfs1:
total 0
-rw-rw-rw- 1 root root 12 Sep  6 20:14 hello.txt

yfs2:
total 0
-rw-rw-rw- 1 root root 12 Sep  6 20:14 hello.txt
% cat yfs2/hello.txt 
Hello world

Afterwards, be sure to stop your all the processes:

% ./stop.sh

If you try the above commands without implementing the required SETATTR, WRITE and READ operations, you will get an error.

Your Job

Your job is to implement SETATTR, OPEN, WRITE, and READ FUSE operations in fuse.cc. You must store the file system's contents in the extent server, so that you can share one file system among multiple yfs_clients.

If your server passes the tester test-lab-3.pl, then you are done. If you have questions about whether you have to implement specific pieces of FUSE functionality, then you should be guided by the tester: if you can pass the tests without implementing something, then don't bother implementing it. Please don't modify the test program or the RPC library in any way; we will be using our own versions of these files during grading.

The test-lab-3.pl script tests reading, writing, and appending to files, as well as testing whether files written on one yfs_client instance can be read through a second one. To run the tester, first start two yfs_clients using the start.sh script. It runs two yfs_client processes each mounting the same file system under a different name (yfs1 or yfs2).

% ./start.sh

Now run test-lab-3.pl by passing the yfs1 and yfs2 mountpoints. Since the script tests each yfs_client sequentially, we do not need to worry about locking for this lab.

% ./test-lab-3.pl ./yfs1 ./yfs2
Write and read one file: OK
Write and read a second file: OK
Overwrite an existing file: OK
Append to an existing file: OK
Write into the middle of an existing file: OK
Check that one cannot open non-existant file: OK
Check directory listing: OK
Read files via second server: OK
Check directory listing on second server: OK
Passed all tests
% ./stop.sh

If test-lab-3.pl exits without printing "Passed all tests!" or hangs indefinitely, then something is wrong with your file server.

Detailed Guidance

• Implementing SETATTR

  The operating system can tell your file system to set one or more attributes via the FUSE SETATTR operation. As always, see the FUSE lowlevel header file for the necessary function specifications. The to_set argument to your SETATTR handler is a mask that informs the method which attributes should be set. There is really only one attribute (the file size attribute) you need to pay attention to (but feel free to implement the others if you like), which has the corresponding bitmask, FUSE_SET_ATTR_SIZE. Just AND (i.e., &) the to_set mask value with an attribute's bitmask to see if the attribute is to be set. The new value for the attribute to be set is in the attr parameter passed to your SETATTR handler.

  Note that setting the size attribute of a file can correspond to truncating it completely to zero bytes, truncating it to a subset of its current length, or even padding bytes on to the file to make it bigger. Your system should handle all these cases correctly.

• Implementing OPEN/READ/WRITE:

  You are free to store the file contents however you like with the extent_server. You may, for example, treat a file's contents as a std::string. (If so, how would you support very large files? We would not test your FS for large files, but it's a good design exercise.)

  READ/WRITE operations are straightforward. A non-obvious situation may arise if the client tries to write at a file offset that's past the current end of the file. Linux expects the file system to return '\0's for any reads of unwritten bytes in these "holes". See the manpage for lseek(2) for details.

Handin procedure

Prepare a tar file by executing these commands:

% cd ~/ds-class/lab
% make clean
% cd ..
% tar czvf yfs-lab3.tgz lab/

That should produce a file called yfs-lab3.tgz in your ds-class/ directory. Go to submit site to upload yfs-lab3.tgz

You will receive full credit if your software passes the same tests we gave you when we run your software on our machines.

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