15 Dec
2022
15 Dec
'22
8:18 p.m.
On Thu, Dec 15, 2022 at 9:07 AM Larry McVoy <lm(a)mcvoy.com> wrote:
On Thu, Dec 15, 2022 at 09:02:08AM -0500, Dan Cross
wrote:
I don't know if they did historically, but I kind of doubt it; QNX predates
4.2BSD, and I imagine there wasn't much influence from TENEX/PMAP).
But they seem to now:
https://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.getting_start…
No idea how they handle page caching. That's an interesting question,
given how they adopted POSIX and try to at least give the outward
appearance of being Unix-y.
Given the emphasis on the message-based architecture, where messages
can be sent between nodes, I doubt there's that much support for shared
memory as a basis for IPC; I think they favored explicit messaging copying
facilitated by the ukernel. Whether you could build something bespoke using
the provided primitives is another matter.
- Dan C.
On Thu, Dec 15, 2022 at 12:38 AM Bakul Shah
<bakul(a)iitbombay.org> wrote:
My mind went to similar thoughts. How did QNX manage the page cache?
Did they have mmap? Don't see how unless they put multiple
related services in the same
address space, which reduces context switching but tends toward a
monokernel (& increased coupling). Unless I am misunderstanding you.
I don't see why two services in a microkernel couldn't arrange to
share a region of memory and implement bidirectional queues
between themselves. With an appropriate signalling mechanism,
you'd still be context switching but avoiding a lot of copying.