CS380L: Advanced Operating Systems

Emmett Witchel

Assignment #2

User-level file system

The goal of this assignment is to create a user-level networked file system

Download and install FUSE. Write a simple networked file system. During the mount, you should specify the remote server name. Make sure the remote system is one to which you can ssh. Whenever you get a request for a file, copy the entire file (using scp or sftp or libssh, hence the need for ssh access) from the remote server and cache it in /tmp or /var/tmp, then service the requests locally.  Copy modified files back when the file is closed. You may use rcp or libssh or another alternative to scp for the file transfer.

Compare your file system to NFS. Design an experiment that shows the performance advantage and disadvantage of this scheme relative to NFS.  Your writeup should contain at least one graph, but probably more.

Make sure your implementation can run the following program properly.  It is most useful if foo exists.  You should write and read the same number of bytes.

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <assert.h>

main() {
   int fd0 = open("foo", O_RDWR);
   int fd1 = open("foo", O_RDONLY);
   char buf[100];
   buf[0] = 9;
   buf[1] = 81;
   buf[2] = 'A';
   buf[3] = 'q';
   buf[4] = '0';
   int nb0 = write(fd0, buf, 100);
   int nb1;
   nb1 = read(fd1, buf, 100);
   assert(buf[0] == 9);
   assert(buf[1] == 81);
   assert(buf[2] == 'A');
   assert(buf[3] == 'q');
   assert(buf[4] == '0');
   printf("Wrote %d, then %d bytes\n", nb0, nb1);
   return 0;

Please report how much time you spent on the lab.


If you use ssh/scp, you probably want to put your public key in your authorized_keys file or run ssh-agent so you aren't prompted for a password on every file system transaction.

You can use stat on the server to implement getattr, but you might want to consider a helper program to simplify parsing.

System tools

These exercises are meant to introduce you to certain system tools that you might find useful.

A) Type the following lines (including newlines).  ^D means Ctrl-D.  Please hand in the file session_record, and describe what you learned from the experience.

script session_record

strace cat - > new_file

hi mom


B) Type the following lines. What kind of devices do you see listed?   Sometimes you can use this trick to debug a lack of audio output.  One program might hold /dev/dsp open while another program tries to write to it.  DO NOT hand in the output of this command.

lsof | grep /dev

C) Copy this file tcpdump.out to your local disk.  This is a trace of packets from a machine called garcia.  It is mounting a disk over NFS from a host called fagen.  Run the following command, replacing EXPRESSION with a tcpdump expression that will report every packet that originates at fagen and ends at garcia.  How many such packets are there?  Is NFS mounted over TCP or UDP?  Speculate on the nature of all UDP traffic in the trace. DO NOT hand in the output of this command.

tcpdump -r tcpdump.out EXPRESSION