代做COMP3430、代写C++代写、代做Operating Systems、代写C++程序语言

日期：2019-03-19 09:21

COMP3430

Operating Systems

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Assignment 4: File Systems

Due: April 4, 11:59pm

Write a program that reads a FAT 16-formatted drive. For this assignment we will use disk image -

though you are encouraged to read a USB ash

drive as a raw device (ie. /dev/disk3).

Your program requires 2 functions:

1. Print information about the drive. The command, assuming your program is named fat16,

would be ./fat16 imagename info. Print out the following:

Drive name

Free space on the drive in kB

The amount of usable storage on the drive (not free, but usable space)

The cluster size in number of sectors, and in KB.

2. Output all les

and directories on the drive. The output should look roughly like the output

from tree, where there is the same number of "-" characters as the depth of the le/folder.

The command, assuming your program is named fat16, would be ./fat16 imagename

list

Output should look something like:

file.txt

Directory: FOLDER

-Directory: FOLDER2

--Directory: FOLDER3

---File: THEFILE.TXT

file2.txt

3. Be able to fetch, and return a le

from the drive

3/18/2019 Assignments - COMP3430

http://www.cs.umanitoba.ca/~comp3430/assignments/assignment4/ 2/4

The command, assuming your compiled program name is fat16, would be ./fat16

imagename get path/to/file.txt

To work with the disk / disk image, use the low-level, unbuered

open, close, read, write, and

lseek system calls. This will save you headaches, buering,

conversions, etc., and let you work

on the byte level.

You have been provided with a Microsoft white paper on their FAT le

systems (Fat12/16/32). You

will only worry about the FAT32 short name implementation so you should use your

discretion on reading.

Also, the minimal header le

fat.h provides a struct data structure for the boot sector. In

addition to any other data structures you may need for your implementation, you will need to

create a similar struct for the FSInfo type. Note the datatypes used instead of the standard int,

etc. Note carefully the #pragma commands used and use them for any structures that you tie

directly to reading from disk (what do these do and why are they important?

http://en.wikipedia.org/wiki/Data_structure_alignment)

Finally, you've been provided with a disk image for testing.

Directories

Directories (aka folders) are simply les

on disk with a special format. There are some good

things to note before reading a directory:

The rst

byte of an entry tells you things such as whether the entry is empty or if it’s the last

entry.

You will nd

empty entries interspersed through the directory. Do not stop searching on an

empty entry! Only the last one!

A directory le

can be quite large and span multiple clusters (Check in the FAT!), so don’t just

stop at one cluster.

The most confusing part here is that you will nd

what appear to be garbage entries.

Fat12/16 only supported 8-character le

names with a 3-character extension. Fat32 added

long lename

support but did it in a way that is backward compatible - old Fat12/16

systems would only see an 8-char version. E.g., le

somelongfilename would show up as

SOMELO~1 - you may have seen such les

up until the mid 2000's. The full lename

is

hidden across several extra added directory entries. For this assignment we will use the

short names only (much simpler) and can skip the ller

entries. Note that you can lter

out

these unwanted long-name additional entries by ltering

against the ATTR_LONG_NAME

attribute.

An additional side eect

is that everything in FAT12/16 was uppercase, so you should stick

to uppercase

Directory entries inside a directory point to the cluster where another directory le

is stored

- look in that le

to see what is in the directory

Memory and Data Types

3/18/2019 Assignments - COMP3430

http://www.cs.umanitoba.ca/~comp3430/assignments/assignment4/ 3/4

Integer overows

and memory layout and alignment are serious issues in this assignment. Note

#pragma comment above. When dealing with addressing specic

bytes of a le

(or disk.) and you

seek using the lseek command, you can easily get bytes addressed well out of range of a

standard 32 bit integer, particularly if it is signed. When dealing with addresses use the explicit

uint32_t family of types to be sure you have enough memory, and use the off_t type (le

oset,

as in man lseek) to be safe. In addition, you will want to add the following line to the TOP

of your main source le

before you load the system libraries:

#define _FILE_OFFSET_BITS 64

This tells the compiler to make the off_t 64 bits wide instead of 32 bits. This is more important if

you are implementing FAT32 (the bonus). Further, it is recommended that you think of reading

and writing to disk in units of sectors and clusters. Not only for eciency

reasons, but it will help

you conceptualize the assignment a lot easier. Try to work in sectors and clusters as much as

possible and only convert to bytes when necessary (e.g., when doing a seek and read)

Disk layout

1. Reserved Area - boot sector and bios parameter block (BPB) at sector 0 (1 sector only).

Read sector 0 directly into the fatBS struct provided.

2. FAT Area - File allocation table (list of 16-bit entries). Immediately follows the reserved area.

3. Data Area - Most of the disk. All the le

data is stored in here, directory entries are stored

in here. NOTE: The rst

cluster of this area is ocially

called Cluster 2 regardless of where it

starts on the disk. The space used by the proceeding two areas is quite denitely

more than

2 clusters large (which would only be ~8k on many disks) luckily, from here the following

clusters are of the appropriate size.

Notes

The top 2 addresses of the FAT are are signatures. You must validate these signatures

before using the le

system

The FAT can be quite large so do not load the entire FAT into memory at once.

Be very careful with unit types! You will need to work in sectors, clusters, and bytes, at

dierent

times. Maybe create functions to convert the types.

How to get started (just suggestions)

1. You will most likely get overows,

null pointers, etc. Some bad math and who knows where

you'll end up on disk (or in memory!). Be extremely defensive in your programming.

2. Check parameters, ranges, and printf meaningful error messages. This will save you

debug time

3. First, load and parse the boot sector / BPB into the struct and write your info function as

much as possible. CHECK THE SIGNATURE BYTES. This tells you if you loaded it correctly.

4. Calculate the location of the FAT and check the FAT Signature

3/18/2019 Assignments - COMP3430

http://www.cs.umanitoba.ca/~comp3430/assignments/assignment4/ 4/4

5. Implement methods to read specic

fat items for disk clusters

Handin

Include a makele

to build your assignment, with proper build and clean rules. Make sure to

run make clean before handing in your assignment. A penalty of 25% of your nal

mark

will apply, if your submission contains temporary les

(including the sample disk image! Do

NOT submit it...)

Include a readme, that explains how to build and run your assignment.

Your assignment must run on the CS Aviary lab computers.

A completed copy of your the honesty declaration for this assignment.

Bonus

Implement FAT32, in addition to FAT16. Choose the driver appropriately based on the signature.