Question $3$: xv$6$ System Call $($Max Mark: $40/100)$

This question requires you to modify the source code of xv$6-$riscv. Make sure you start with a fresh copy of the original xv$6$ code.

There is a ps command on Linux and on MacOS. You are required to implement a simple version of the ps command for xv$6.$ You should first become familiar with this command on Linux or MacOS. Documentation of this command can be displayed using the man ps command, while ps $--$help all will list all the options available in a shorter format.

Task $1$: Implement a simple version of the ps command on xv$6-$riscv. When used without any command$-$line argument, this command should display information of all current processes in xv$6$ that are either running or sleeping. The information should include:

Process ID

Parent process ID

State

Name of process

Size $($in bytes$)$

An example of the command and output is as follows:This information can be found in the process table in the kernel part of the xv$6$ code. It is an array of struct proc, one structure per process. You may only access it from code running in kernel mode. Hence you will need to implement a system call that displays this information for you. In addition, you will need to write the ps program as a user program.

Task $2$: Modify your ps program to check for any command$-$line arguments. If the argument is $-r$ then display only the information of the running process. If the user enter any other argument, an error message should be displayed instead. Since you have not learnt how to pass information through a system call yet, a simpler way is to set up another system call to display this.

An example output:

$ ps $-$r

$42$ running ps $12288$