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School of Computer Science & Engineering
University of New South Wales

 Advanced Operating Systems 
 COMP9242 2007/S2 

M7: Process management

Currently your operating system has only been able to run one process, probably sosh. In this milestone you will implement the process related system calls: process_create, process_delete, my_id, process_status and process_wait. Obviously each new process should run it its own address space. This will require you to carefully manage L4 memory spaces.

Currently process_create need only run executables contained within the DITE image, and need only run these executables in-place, and only run them successfully once.

You are supplied with a sos_get_binfo_rec function which iterates over the entries of the dite image. sos/main.c:init_thread has an example of how to iterate over the entries.

sosh has an exec command. This command provides a simple interface to the process_create system call. In a similar style to UNIX shells, if the third argument to exec is an '&' then it will run the process in the background. Otherwise sosh will use process_wait to wait until the child process has finished executing.

To add more executables to the bootimg.bin file you will need to create more newapp = app_env.Application("newapp") in the top-level SConstruct file. In the Bootimage command you can append a comma seperated list of new applications. Each of these images will automatically be added to the dite image.

NOTE: The stime and ctime fields of the process_t data structure are optional. Unlike previous versions of L4, Pistachio does not maintain these values for you.

Design issues

As with most milestones, a lot of the design work will be working out suitable data structures to hold process information. You may also need to extend other data structures in your operating system to handle multiple processes.

You also probably want to change your crt so that when a process's main function exits it will kill itself.


You should show sosh executing a sub-process and show that the ps command works. As processes will be running in-place you need only execute each one once.

You may want to add a kill command to sosh to show that process_delete works.

As always you should be able to explain the data structures and algorithms used.

Last modified: 27 Jul 2007.