Task $3$: Directory Space Usage $[40$ points$]$

In this question, you have to write a program $($myDU$.$c$)$ that finds the space used by a directory $($including its files, sub$-$directories, files in sub$-$directories, sub$-$sub directories etc.$).$ Let$$s call this directory as

the Root directory.

Syntax

$$./$myDU

Example

Figure $3$: Example to illustrate the use of directory space usage finding utility

Figure $3$ shows the structure of a directory called Documents which is the designated Root directory

in this example. This directory contains files such as Bill$\_$Payment.pdf$,$ Experiment$\_$Results.txt and

a sub$-$directory called Office. The Sub$-$directory Office contains a file named Deals.ppt$.$ To find the

size of the Documents directory, its name is passed as $$./$myDU Documents. Your utility is expected

$4$

to print the total size of the contents of the passed root directory in bytes $($For eg: $20284).$ Note that,

this is inclusive of directory sizes.

Output

Only print the size of the Root directory in bytes $($Refer to Figure $3)$

Detailed instructions

To make the calculation process more efficient, we propose a method where different sub$-$directories

under the Root directory will be processed by different processes. The exact working is detailed in the

following points.

$$ Assume that there are N immediate sub$-$directories under the Root directory. For each immediate

child sub$-$directory under the provided Root directory, your program must create a new process

Pi $($i will range from $1$ to the total number of immediate sub$-$directories under Root$).$ Each child

process Pi should find the size of the i

th child sub$-$directory $($including all files and directories

under it and the size of the sub$-$directory itself$)$ and pass this information back to the parent

process. Parent process should find the size of the files immediately under it along with the Root

directory size. Finally, parent process will find the sum of all sizes and print the final output.

Figure $4$: Sample directory structure

For example: In Figure $4,$ there are two immediate sub$-$directories $($HTML$,$ CSS$)$ under the Root

directory $($Tutorials$).$ In this case, the parent process should create two child processes, say,

P$1$ and P$2.$ P$1$ should calculate the size of the sub$-$directory $($HTML$)$ which is a sum of sizes

of all files and directories under HTML including the size of HTML itself. Similarly, P$2$ should

calculate size of the directory CSS$.$ Both P$1$ and P$2$ should return the result back to the parent

using pipes. Finally, the parent process would find the size of the files immediately under it

$($Payment$\_$receipt.pdf$,$ Description.txt$)$ and the size of the Tutorials directory to report the

final result.

$5$

$$ Your program should only use pipes $($pipe$()$ system call$)$ to communicate between parent process

and the child processes. There is no restriction on the number of pipes to be used.

Figure $5$: Example to illustrate the handling of symbolic links by $./$myDU utility

$$ A symbolic link is a special type of file in Linux that points to another file or directory. Symbolic

links can be present anywhere in the Root directory tree. You should resolve the symbolic links

and find the size of the file$/$directory pointed by a symbolic link instead of reporting the size of

the symbolic link file $($Refer figure $5).$ It can be assumed that a symbolic link will never point to

itself recursively. For example, in Figure $5,$ Taxes$22\_23$ directory will not contain a symbolic link

that points to the Taxes$23\_24$ directory or directly to the Sym$\_$link$\_$to$\_$Taxes$22\_23$ symbolic file

in the Taxes$23\_24$ directory.

$$ It is the responsibility of the parent process to find the size of the file$/$directory pointed by a

symbolic link which is present immediately under Root directory. For example, in Figure $5$ parent

process will not create any child process. However, if a symbolic link is present in a sub$-$directory,

it should be processed by the child process handling the sub$-$directory.

$$ During testing, only relative path of the Root directory will be passed to the $./$myDU utility. It

can be assumed that the size of the directory path generated during testing will not exceed $4096$

characters.

$$ You can assume that the total size of the Root directory will fit in a $8-$byte integer type $($i$.$e$.,$

unsigned long on $64-$bit machines$)$

Error handling

In case of any error, print $$Unable to execute$$ as output.

System calls and library functions allowed

$-$ fork $-$ malloc

$-$ exec$*$ family $-$ free

$6$

$-$ pipe $-$ stat

$-$ opendir $-$ lstat

$-$ readdir $-$ readlink

$-$ closedir $-$ strlen

$-$ read $-$ open

$-$ write $-$ close

$-$ strcpy $-$ strcat

$-$ strcmp $-$ strto$*$ family

$-$ ato$*$ family $-$ wait$/$waitpid

$-$ printf family $-$ exit

$-$ dup $-$ dup$2$

Testing

Refer to README document