[TUHS] Dynamics between BSD and Linux

Theodore Ts'o tytso at mit.edu
Sat Feb 3 03:00:28 AEST 2018

On Wed, Jan 31, 2018 at 01:39:25AM -0700, Kevin Bowling wrote:
> Linux has been described as influenced by Minix and System V.  The Minix
> connection is well discussed.  The SysV connection something something
> Linus had access to a spec manual.

For many of us it was POSIX.1 1990.  I implemented Job Control from
the POSIX.1 spec, and then recompiled bash, and it worked the first
time out of the box.  The Berkeley man pages are not bad, but the
POSIX spec was much more of a formal POSIX spec.

> But I’d guess reality would be more gradual — new contributors that
> liked CSRG BSD would have mostly gravitated to the continuations in
> 386/BSDi/Net/Free that were concurrent to early and formative Linux
> development.. so there’d be an implicit vacuum of BSD people for
> Linux development.

I'll note that my first experiencing hacking kernels was the BSD
4.3+Reno; but it was mostly what I perceived as the toxicity of a
certain core team member (way worse than the caricature of Linus as
portrayed by the press) that caused me to decide to stick with Linux
than with *BSD.

> The kinds of BSD things I am talking about are ufs, kqueue, jails, pf,
> Capsicum.  Linux has grown alternatives, but with sometimes willful
> ignorance of other technology. It seems clear epoll was not a good design
> from the start.

In some cases, the ideas were carefully considered, and they were
rejected.  For example, Soft Updates was one that we looked and we
decided that it was too complicated, and would restrict who could add
new features to the file system afterwards.  This LWN article, "Soft
Updates, Hard Problems"[1] was written much later, but it's a good
summary of our reasons.

[1] https://lwn.net/Articles/339337/

In other cases, it was a case of parallel evolution.  Work done on
epoll, was at least partially funded by IBM as part of the Linux
Scalability Effort, and the basic design had been fixed in advance.  I
wasn't working on that myself, but I vaguely recall that there were
potential Microsoft patent concerns that constrained the epoll design.

> Despite jails not being taken to the logical conclusion of
> modern containers like zones, the architecture is fundamentally closer
> aligned to how people want to securely use containers versus namespaces and
> cgroups.

The original goal of cgroups and namespace was not for
security/isolation.  Cgroups in particular was something Google had
implemented for to allow a large number of jobs on a single shared
system.  The jobs all belonged to different Google teams/product
groups, so mutually distrustful job owners weren't part of the design
requirements; efficiency to decrease compute TCO was the overarching

Using cgroups for containers is something that a startups like Docker
drove, and "time to market" and "keep the VC's happy" were far more
happy than to "delay product launch for years while we burn VC money
to reimplement BSD jails".

> This seems strange to me as BSD people are generally open to other /ideas/,
> we have to be careful with Linux code due to license incompatibility, but
> the converse is does not seem true either in interest in other ideas or
> license hampering code flow.

I'll note that I implemnted e2fsck using a lot of ideas about how to
speed up fsck for the BSD FFS from a paper published in the 1989
Usenix conference in Baltimore.  The core idea was to cache data and
cleverly reorder how various consistency checks were done by fsck so
that metadata blocks would not need read more than once in most cases.
These techniques sped up fsck by a factor of 2-3 I contacted the
author and was told those ideas were never picked up by BSD.  Oh well,
BSD's loss, Linux ext3's gain.  :-)

> The history of UNIX is spectacularly successful because different groups
> got together at the table and agreeed on the ideas.  Is there room for that
> in the modern era where Linux is the monopoly OS?  The Austin Group is
> still a thing but it’s not clear people in any of the Freenix communities
> really care about evolving the standards.  I get that, but not so much
> completely burrying ones head in the sand to what other OSes are doing.  Is
> there any future for UNIX as an “open system” in this climate or are people
> going to go there separate ways?

I don't think it's really about "wilful ignorance".  It's more about
economic considerations and what you can get your employer to pay for.
I can think of a lot of times were my design was driven by the amount
of headcount I could get authorized, and how much time I had before
code freeze for this year's Android release.

Some of these considerations don't apply if the work is done by
starving hobbiest, or by academics who can use cheap grad student
labor.  But I suspect here have also be cases where "minimal
publishable unit" has also driven the way certain work has landed
into, for example the Coda File System, which I was told "contained
the remanants of a dozen Ph.D. theses", and was the code was too ugly
and debt-ridden to be salvaged.  (Which is why Intermezzo was started;
alas, that never went anywhere.)

						- Ted

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