> you mean, the all 9 subsystems works through 9P and filesystems, > that safe for kernel?
the kernel doesn't actually implement all that much, and most complex things are outside the kernel. the biggest exceptions are networking and low-level device drivers, but the interface to those is small, or even tiny. the device drivers aren't that big either. the network has been in and out of the kernel at different times over the years. qnx is probably the most reasonable so-called microkernel i've seen described (but i haven't seen their code).
