iPodLinux Operating System Project: Implementing a System Call | Study Guides, Projects, Research Operating Systems

CMSC 321 — Operating Systems

iPod Project

iPodLinux System Call(s)

Due: 18:45 Friday 04 May 2007

Overview: For this final project you will implement one or more system calls in the iPodLinux kernel and

provide user-level test program(s) for testing your system calls.

This project must be done individually, without assistance from anyone else but me. You are free to use any

textbooks or online resources that you may find, but you are not allowed to copy code, and you must cite

any resources that you used.

Minimum Requirements: To meet the minimum requirements for this project, you must implement a

system call that mimics the ps (process status) command — man ps for more information.

More specifically, for all processes currently executing in the system, for each process you must list the

process id, user id, group id, process start time, and process name. Refer back to the notes from earlier

in the semester on the process image struct task struct located in include/linux/sched.h. Much of the

information to be reported can be found therein, including cycling through the list of active processes. You

may choose, but are not required, to sort the output by process id.

Your output must be returned to the user-level program through a single char* parameter. For successful

completion of the system call, it is the user’s responsibility to have allocated sufficient space for the buffer

into which your system call will place its output. However, you are required in your system call to check if

sufficient space exists at the user level before you attempt to write to the user level (i.e., use verify area).

You system call must include an appropriate return value. Definition of this return value is at your discretion,

but generally 0 indicates success and -1 indicates failure.

Upon successful completion of the system call, the user level program should be able to print the contents of

the string parameter directly and show well-formatted output. In other words, it is up to your kernel-level

system call to handle formatting in the string returned to the user-level. The user-level program must be

able to invoke your system call similar to the following:

int returnValue = syscall(SYSCALL_NUM, psString);

if (!returnValue)

printf("%s", psString);

with resulting well-formatted output that looks something like the following:

pid uid gid Time Name

0 0 0 0 swapper

1 0 0 25 init

2 0 0 26 keventd

...

41 0 0 13553 userTest

(Note that, for iPodLinux, all processes will be run as root, so the user id and group id will always correspond

to root — i.e., zero.)

Items You Need To Know:

•A pointer to the current process is readily available (see include/asm-archnommu/current.h).

iPodLinux Operating System Project: Implementing a System Call, Study Guides, Projects, Research of Operating Systems