Project 2

• In this project, for both Questions 1 and 2, you need to write a new system call my_get_physical_addresses(unsigned int * initial, int len_vir, unsigned int * result, int len_phy) so that a process can use it to get the physical addresses of some virtual addresses.
• The return value of this system call is either 0 or a positive value. 0 means that an error occurs when executing this system call. A positive value means the system call is executed successfully.
• The first argument of this system call is the address of an unsigned integer array. Each element of the array stores a virtual address of a process.
• The second argument of this system call is the number of elements in the array.
• The third argument is the address of an unsigned integer array. Each element with index i of this array stores the physical address of the virtual address stored as element i in the array pointed by the first argument.
• The fourth argument is the number of elements stored in the array pointed by the third argument.

                 //prototype of the new system call is as follows:     

                 int my_get_physical_addresses(unsigned int * initial, int len_vir, unsigned int * result, int len_phy)
               
              

• Two threads show a physical memory cell (one byte) if both of them have a virtual address that is translated into the physical address of the memory cell.
• The kernel usually does not allocate physical memories to store all code and data of a process when the process starts execution. Hence, if you want kernel to allocate physical memories to a piece of code, execute the code first. If you want kernel to allocate physical memories to a variable, access the variable first.
• Inside the Linux kernel, you need to use function copy_from_user() and function copy_to_user() to copy data from/to a user address buffer.
• Check the "Referenced Material" part of the Course web site to see how to add a new system call in Linux.