| OpSys Fall 2006 - HW4 |
| OpSys Home | Assignment | Programs | Requirements | Submitting | Notes |
- Minimal Filesystem
The objectives of this assignment are:
You are to design and partially implement a filesystem that is either a FAT (File Allocation Table) or inode based filesystem. We won't be actually adding the code to Unix kernel, instead we will develop a number of Unix programs that provide access to the filesystem (which will actually occupy a single Unix file).
Your filesystem must support a number of operations (listed below), and must be based on either:
File Allocation Table: a table that provides information about the location of the blocks that make up a file. The FAT basically holds a linked list of block numbers for each file that exists in the file system. It is assumed that the entire FAT is memory resident, so that it is not necessary to read files sequentially (random access is supported).
Inode type filesystem: The information about which disk blocks correspond to a file are stored in a fixed-size data structure called an inode. Each inode contains a list of disk blocks, and possibly a pointer to other inodes (if the file is too large to describe with a single inode).
Chapter 6 has a description of both approaches.
For this assignment you only need to support a single directory for the entire filesystem. File names can be alphanumeric strings of up to 255 characters, you do not need to support white space in file names. There should not be any artificial limit on the size of any file (as long as there is enough room in your file system, it should allow a file of any size to be created).
Your filesystem will be stored in a single 2MB Unix file named "myfs". All of the programs described below should assume this file is in the current working directory. The file itself must be a sequence of 4096 blocks of size 512 bytes. Every part of the filesystem must be held in these 2048 blocks (including the FAT or inodes and the single directory).
There is no fixed format for your filesystem other than those described above, the general idea is that you pretend you have a 2MB hard disk with block size 512 bytes, you decide how to represent the FAT or inodes and the single directory. It is not expected that your code will work with anyone else's file.
- File system programs
You must provide all of the programs listed below using the command line parameters indicated. Feel free to support additional command line options. We will use test scripts based on the command lines shown below!
fscreate
The fscreate command
must create the file named "myfs" in the current working directory
and initialize this file to represent an empty file system (a file
system that doesn't happen to hold any files).
fsinsert filename:
The fsinsert
command adds a new file to your filesystem. The name of the new file
is given as the only command line argument. This program should
read the Unix file of the same name (in the current working directory)
and add it to your filesystem
(assuming there is sufficient room). The program should return
a 0 if the file has been added successfully (either have main
return(0), or call exit(0)). If there is
no room for the file, or if there is no such Unix file, the program
should print an error message (and have main return(1)).
Our scripts will use the program status (return value from main), so
you must make sure you set the exit status correctly!
fsremove filename:
The fsremove
command removes a file from your filesystem. This command should
free up any blocks used by this file and update all data structures
(and write the updates to the file "myfs"). This command has
nothing to do with the Unix filesystem, you should not delete any
Unix files. The program should set the exit status to 0 if there
removal works, 1 if there are any problems (perhaps the named
file doesn't exist) and print an error message.
fscat filename:
The fscat command
prints the contents of the named file (in your filesystem) to stdout.
Use write, not printf or cout (so you can handle binary
files). Set the exit status as in the other commands (0 if everything
is OK, 1 if there is any problem).
fsls:
The fsls command should
print out the names and sizes of all files contained in your
filesystem.
fsmap:
The fsmap command should
print out a string that depicts the block usage of your filesystem.
For each of the 4096 blocks you should print either a "*" meaning the
block is currently used, or a '-' (minus) if the block is free. The
output of this command should look something like this:
***************************--*************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ******************************************************************************** ***********------------------------***------------------------**---------------- ---------****-------------------------****------------------------***----------- -------------**------------------------***---******-***------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- ---------------- |
fsinfo filename:
The fsinfo command
should print information about the named file to standard output. The
information printed must include:
If the named file does not exist in your filesystem, print an error message and set the exit status to 1.
- Project Requirements
The following are the requirements for the project:
Your programs can be written in C or C++ and
must compile and run on the CS department
FreeBSD machines (freebsd.remote.cs.rpi.edu).
If you want to consider something other than C or C++,
please ask Dave first.
Your programs must function as described above, with the command line arguments as shown.
Your submission must include a Makefile.
Your submission must include a file named README that includes the following information:
Grading: Your code will be graded according to the formula below. Note that to get full credit we must be able to understand your code (it must be commented!)
| 60% | fscreate, fsinsert, fsremove and fscat commands (these provide minimal functionality). Partial credit is available. |
|---|---|
| 30% | fsls, fsmap and fsinfo commands are worth 10% each). |
| 10% | Code quality (comments, organization, how hard is it to understand ?). |
You can get partial credit for any part.
If your code does not compile and run under FreeBSD, you will lose at least 1/2 the relevant points ( partial credit will be awarded based on visual inspection of the code).
- How to Submit
Log in to WebCT at webct.rpi.edu using your RCS id and password. Once you get to MyWebCT click on "Operating Systems", and from there go to the homework drop boxes. Submit your files (individually, zipped or tarred) to the drop box labeled HW4.
- Notes:
The bulk of the code you need should be shared by your programs. For example, you might create a file named "fat.c" that holds all the FAT related code, a file named "dir.c" that contains all the code related to the single directory you need to support, and a file named "fio.c" that supports actual file I/O to the myfs file. The following might then be a Makefile that would build all your programs:
all: fscreate fsinsert fsremove fscat fsls fsmap fsinfo
SHARED=fat.c dir.c fio.c
fscreate: fscreate.c ${SHARED}
gcc -o fscreate fscreate.c ${SHARED}
fsinsert: fsinsert.c ${SHARED}
gcc -o fsinsert fsinsert.c ${SHARED}
fsremove: fsremove.c ${SHARED}
gcc -o fsremove fsremove.c ${SHARED}
... and so on...
|
Note that the partial Makefile above compiles all the shared .c files for each executable (which is inefficient!). If you read up on Make you can certainly build a better Makefile that links object modules (.o files) instead...
SPEND SOME TIME PLANNING! You will save lots of time on this assignment if you take the time to design your filesystem first, then build parts of the support code (and test each part individually when possible). This project is not particularly hard (there is no difficult programming) as long as you are organized. If you try to write each program as a single main() function you will waste lots of time!!!
There is probably very little use for any str
functions (and C library function starting with the prefix "str")!
File names are strings, but you should never treat the contents of a
file as a string. We will test your code on binary files (images, executables, etc).