Part I: Virtual Memory Questions

$1.$ A certain computer provides its users with a virtual$-$memory space of $232$ bytes. The

computer has $218$ bytes of physical memory. The virtual memory is implemented by

paging, and the page size is $4096$ bytes. A user process generates the virtual address

$11123456($this is in hexadecimal $($base $16)).$ Explain how the system establishes the

corresponding physical location. Distinguish between software and hardware

operations. Feel free to use a diagram $($simple ASCII is fine$)$ if you wish, but that$$s

not required.

$2.$ Assume we have a demand$-$paged memory. The page table is held in registers. It takes

$8$ milliseconds to service a page fault if an empty page is available or if the replaced

page is not modified, but $20$ milliseconds if the replaced page was modified. Memory

access time is $100$ nanoseconds.

Assume that the page to be replaced is modified $70\%$ of the time. What is the

maximum acceptable page$-$fault rate for an effective access time of no more than $200$

nanoseconds? Show your work

Coding:

$$ Write UnixLs, a program that emulates ls$,$ in UnixLs.c

$$ Implement only the following options:

$1.-$i

$2.-$l

Testing:

$$ To test the program simply run the program and specify the options the same way

you would for the ls command. Be sure to test every option you have

implemented and all the permutations of the various options $($e$.$g$.-$il$,-$i$,-$li$,-$l$,$

etc.$)$ Of course, don't forget the most obvious test of all, no options. You can

determine if your output is correct by observing what ls with similar options

produces.

The output of your program should mimic the standard ls command with the following

exceptions:

$1.$ You should require that any options $(-$l $-$il $-$i$)$ to your command come before any

directory names. The standard ls command allows options to appear between and

after directory arguments.

$2.$ File listing order does not have to be identical to ls$.$ You may list the files in whatever

order is convenient for you rather than sorted alphabetically as ls normally does.

$3.$ To simplify the printing of dates, you are to use the format

mmm dd yyyy hh:mm

regardless of the date. An example date would look like:

Oct $2201913$:$32$

The real ls command omits the year if the date is less than a year in the past and

replaces the minutes and seconds with the year if the date is more than a year in the

past.

$4.$ When performing a long listing $(-$l$)$ there is no need to print the line that begins with

"total".

$5.$ You should print the files one per line $($as ls $-1$ does, rather than attempting to format

the list of files into multiple columns.

Here are a few other test cases you should try:

$\%$ ls $-$i ~$/$

$\%$ ls $-$l

$\%$ ls $-$i $-$l $..$ ~

$\%$ ls $-$li $...$ ~

Then replace $"$ls$"$ with "UnixLs". The output should be very similar to the original ls

command; however the order with which you list the entries is allowed to be different.

Also note that you may have an alias for ls that provides some arguments all the time. To

see if you have an alias for ls$,$ type alias ls$,$ and to make the alias go away $($for the

duration of the life of your current shell$)$ type unalias ls$.$

Hints

$$ Focus on extracting the proper information and just printing it$.$ Once you have

that all done work on making the format match the ls command.

$$ Consult the the provided file infodemo.c to see what calls to use to get actual

group and user names.

$$ Consult the provided tutorials in the assignments section of the course webpage

for information on UNIX file system structure.

$$ Don't forget to test your code on directories with symbolic links in them.