[TUHS] Re: If forking is bad, how about buffering?

[Andrew Warkentin <andreww591@gmail.com>]

On Sat, May 18, 2024 at 7:27 PM Larry McVoy <lm@mcvoy.com> wrote:
>
> Do any micro kernels do address space to address space bcopy()?
>

QNX and some L4-like kernels copy directly between address spaces. QNX
copies between readv()/writev()-style vectors of arbitrary length.
L4-like kernels have different forms of direct copy; Pistachio
supports copying between a collection of "strings" that are limited to
4M each. seL4 on the other hand is limited to a single page-sized
fixed buffer for each thread (I've been working on an as-yet unnamed
fork of it that supports QNX-like vectors for the OS I'm working on; I
gave up on my previous plan to use async queues and intermediary
buffers to support arbitrary-length messages in user space, since that
was turning out to be rather ugly and would have had a high risk of
priority inversion).