jiangyy / mosaic

The MOSAIC Operating Systems Model and Checker

MOSAIC Operating System Model and Checker

This is the artifact for Paper #202 of USENIX ATC'23 "The Hitchhiker’s Guide to Operating Systems". (Cherry-picked from the backend of my course homepage.)

• mosaic.py - The model checker (zero dependency; self-documented)
• vis/ - The visualization script of an interactive state space explorer
• examples/ - The code examples evaluated in the paper

The Operating System Model

MOSAIC supports simple applications with "system calls". The program entry is main():

def main():
    pid = sys_fork()
    sys_sched()  # non-deterministic context switch
    if pid == 0:
        sys_write('World\n')
    else:
        sys_write('Hello\n')

MOSAIC can interpret these system calls, or model-check it:

python3 mosaic.py --run foo.py
python3 mosaic.py --check bar.py

A JSON file (state transition graph) will be printed to stdout. The output (state transition graph) can be piped to another tool, e.g., a visualization tool:

# quick and dirty check
python3 mosaic.py --check examples/hello.py | grep stdout | sort | uniq

# interactive state explorer
python3 mosaic.py --check examples/hello.py | python3 -m vis

Modeled System Calls

System Call	Behavior
sys_fork()	create current thread's heap and context clone
sys_spawn(f, xs)	spawn a heap-sharing thread executing f(xs)
sys_write(xs)	write string xs to a shared console
sys_bread(k)	return the value of block id k
sys_bwrite(k, v)	write block k with value v
sys_sync()	persist all outstanding block writes
sys_sched()	perform a non-deterministic context switch
sys_choose(xs)	return a non-deterministic choice in xs
sys_crash()	perform a non-deterministic crash

Limitation: system calls are implemented by yield. To keep the model checker minimal, one cannot perform system call in a function. (This is not a fundamental limitation and will be addressed in the future.)

Reproducing Results

python3 examples/_reproduce.py

Similar results in Table 2 are expected. Tested on: Python 3.10.9 (macOS Ventura), Python 3.11.2 (Ubuntu 22.04)