[TUHS] Systematic approach to command-line interfaces

Greg A. Woods woods at robohack.ca
Wed Sep 29 03:46:25 AEST 2021

[[ I'm digging through old mail -- my summer has been preoccupied by
things that kept me from most everything else, including computing. ]]

At Sun, 1 Aug 2021 18:13:18 -0600, Andrew Warkentin <andreww591 at gmail.com> wrote:
Subject: Re: [TUHS] Systematic approach to command-line interfaces
> There's a third kind of primitive that is superior to either spawn()
> or fork() IMO, specifically one that creates a completely empty child
> process and returns a context that lets the parent set up the child's
> state using normal APIs.

That's actually what fork(2) is, effectively -- it sets up a new process
that then effectively has control over its own destiny, but only by
using code supplied by the parent process, and thus it is also working
within the limits of the Unix security model.

The fact that fork() happens to also do some of the general setup useful
in a unix-like system is really just a merely a convenience -- you
almost always want all those things to be done anyway.

I agree there is some messiness introduced in more modern environments,
especially w.r.t. threads, but there is now general consensus on how to
handle such things.

I'll also note here instead of in a separate message that Ted's followup
questions about the API design and security issues with having the
parent process have to do all the setup from its own context are exactly
the problems that fork() solves -- the elegance of fork() is incredible!
You just have to look at it the right way around, and with the Unix
security model firmly in mind.

I personally find spawn() to be the spawn of the devil, worse by a
million times than any alternative, including the Multics process model
(which could have made very good use of threads to increase concurrency
in handling data pipelines, for example -- it was even proposed at the
time).  Spawn() is narrow-minded, inelegant, and an antique by design.

I struggled for a very long time as an undergrad to understand the
Multics process model, but now that I know more about hypervisors
(i.e. the likes of Xen) it makes perfect sense to me.

I now struggle with liking the the Unix concept of "everything is a
file" -- especially with respect to actual data files.  Multics also got
it right to use single-level storage -- that's the right abstraction for
almost everything, i.e. except some forms of communications (for which
Multics I/O was a very clever and elegant design).  The "unix" nod to
single level storage by way of mmap() suffers from horribly bad design
and neglect.

					Greg A. Woods <gwoods at acm.org>

Kelowna, BC     +1 250 762-7675           RoboHack <woods at robohack.ca>
Planix, Inc. <woods at planix.com>     Avoncote Farms <woods at avoncote.ca>
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