Kernel Mysyslog Project

by: burt rosenberg
at: university of miami
date: 22 sep 2021

  
   
NAME
    my_syslog -- kernel syslog system call
    mysyslog -- command line interface to my_syslog
    
SYNOPSIS
    takes a string argument, and kernel syslogs the string

DESCRIPTION
    The my_syslog takes a string argument, and kernel syslogs the argument. 
    It always returns 0.
    
    The mysyslog command calls my_syslog on the first argument.

HISTORY
    Introduced as Project 2 in CSC521 session 131.
    Made a separate project in csc421 session 191.
	
BUGS

Goals

The goals of this project are:

To build a custom Linux kernel.
To learn the syscall interface, and to add a system call.
To interface to the system calls by user programs and libraries.

The M1/M2 Mac

Virtual box does not run on the M1/M2 macs. Use QEMU is an alternative.

    Install qemu using brew:
    
    brew install qemu
    brew install wget
    
    Make an empty virtual image:
    
    qemu-img create myimage.img 32G
    
    Get the ISO from:
    
    wget https://releases.ubuntu.com/16.04/ubuntu-16.04.6-server-i386.iso
    
    and install it:
    
    qemu-system-i386 -drive file=myimage.img,format=raw,index=0,media=disk -cdrom ubuntu-16.04.6-server-i386.iso -boot d -m 2048
    
    then control-C and restart without the cdrom,
    
    qemu-system-i386 -drive file=myimage.img,format=raw,index=0,media=disk -m 2048
    
    (Note: previously qemu-system-i386  -hda myimage.img -cdrom ubuntu-16.04.6-server-i386.iso -boot d -m 2048)
    
    However this is very slow. Please allow hours of time for your initial kernel build.

Specific steps: Build the Linux Kernel

Build the linux kernel. Here are instructions.
Note: The build takes at least two hours.
Rebuild and reboot on the new kernel.
Ascertain you are on your new kernel by looking for tag in the output of "uname -r"
Make sure you have changed the name of your kernel, and are booted on the new kernel.
Copy [repo]/class/proj2/Makefile to your proj2 directory.
Run "make uname-out" to confirm you have the right kernel.

Specific steps: Add a Syscall to the Linux Kernel

Modify the kernel files to introduce the system calls. Here are hints.
Rebuild and reboot on the new kernel.
Test mysyslog. The evidence.tar file will be created.
Modify the Makefile, adding a myevidence target. This target will create an evidence.out file that contains the exit status of mysyslog when run with message "Captain Kernel has arrived", the line from the syslog showing the syslog'ed Captain Kernel message, and the output of uname -r, in that order.
svn add evidence.tar and myevidence.out, and commit.

Notes about the syscall entries

When you modify the syscall table, the entire kernel will be rebuilt. This is because everything depends on the syscall table. I have shown modifications that in this iteration of kernel modification include four new syscalls, but we are right now only concerned with the first of these four. You can include all four now, saving a long kernel build later, but you must satisfy external dependencies by providing stub programs that have the name of the yet unimplemented syscalls, that just return with a default -1 value. Or you might ignore this for now, but do that consistently among all the files involved.

Testing and submission

Test-mysyslog sends the string "hello kernel!" to the system log. It then saves the return value of mysyslog and the most recent occurence of a syslog message containing "hello kernel!" to a mysyslog.out file. Because the output can vary, there is no mysyslog.ref file. The file mysyslog.out will be judged informally.

Please read the makefile and understand what is going on.

You will submit "evidence" that your project ran, as well as the sources so that we can reproduce your project.

The makefile target evidence collects the evidence into an evidence.tar file, which you will add and commit to the repository. The evidence includes of the 5 kernel files and the output file:

kernel/mysyscalls.h
kernel/mysyscalls.c
entry/syscalls/syscall_32.tbl
linux/syscalls.h
kernel/Makefile
evidence.out

You will then modify the makefile to create a myevidence target. This target will build mysyslog if needed (what should be the dependency of the target?) and run it with argument "Captain Kernel has arrived". A myevidence.out file is created with,

mysyslog's exit status
the line from the syslog file that shows the syslog'ed message "Captain Kernel has arrived"
the result from the uname -r command.

You must add and commit the complete set of sources that built and tested your project:

Makefile (modified)
mysyslog.c (modified)
mysyslog.h (can be unmodified)
evidence.tar (created)
myevidence.out (created)

This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

author: burton rosenberg
created: 27 sep 2015
update: 19 aug 2022