Exercise #4

Read lesson 5 then 6 on creating a system call.

1. Create two counters inside of the Xv6 kernel to count the number of bytes read and written via the read()/write() system calls. Then create a system call to get the values of those two counters. You may decide for yourselves the names of the counters and system call and its API.

   Consider placing the system call in the sysproc.c file.

2. Make a user-space program (iostat.c) that uses the system call. With no parameters it should just read and print the current values. With an integer value (N) it should loop and print the values while sleeping every N seconds. The sleep() system call sleeps about 100 ticks / second (so multiply N by 100 to get the number of ticks to give sleep().)

3. The files you will likely need to modify will probably include at a minimum:

    Makefile
    syscall.h
    syscall.c
    sysfile.c
    usys.S
    user.h
    iostat.c

Note that the xv6-public found in the "Class Code" section for this course has all the solutions to all the exercises (and all the other things done during the course) already found within it.