[TUHS] VFS prior to 1984
gingell at computer.org
Thu Jun 25 10:56:58 AEST 2020
On 6/24/2020 11:31 AM, Paul Ruizendaal wrote:
> I came across this 1979 paper by P.M. Lu from Bell Labs Naperville
> The abstract says:
> "RIDE (Resource-Sharing in a Distributed Environment) ...
RIDE seems very reminiscent of the RSEXEC (Resource Sharing EXEC) done
on TENEX earlier in the 1970s. The implementation of RSEXEC involved
encapsulation of a process fork by its parent rather than an
object-oriented abstraction inserted behind an existing interface like
VFS is. Both are functionally transparent to their users but are kind of
going in opposite directions in implementation.
As with other mechanisms that have been referenced in this thread, these
illustrate the claim that "all problems in computer science can be
solved by [adding] another layer of indirection". I don't know that
that's absolutely true but I've certainly applied it a lot, and like a
lot of things, excessive application can create more problems.
(I never knew who was the first to utter the claim as I've heard it said
by lots of people. However a quick check shows an attribution to David
Wheeler in the form of the "Fundamental theorem of software engineering".)
RSEXEC was a pretty remarkable facility in action. It (approximately)
was like having a command interpreter for the aggregated TENEX resources
of the ARPAnet. It was at least partly intended to serve users of TIPs
(the terminal interface processors used to access hosts) by letting them
treat all TENEXes as a single resource and not worry about which one
they got hosted onto "this time" with respect to their files,
applications, etc., and importantly also not worry about the where their
collaborators were hosted at the moment.
A description of RSEXEC is at:
The encapsulation mechanism was JSYS Traps, JSYS being the system call
instruction on PDP-10s modified to run TENEX. A description of that is at:
In it's way, RSEXEC illustrated one characteristic of many excellent
innovations in that when used as intended it was "deceptively
unimpressive". As in: harder to demo.
NFS and other things share this trait, and indeed early trade show
demonstrations of NFS were frustrating (in those days, the engineers did
booth duty). At first, demos reduced to typing "ls". Which,
unsurprisingly, produced a list of files. It's not until you know how it
was done that it's impressive.
There can be a real utilitarian pleasure in things that, when shown to
others, produce a "yeah, wasn't it supposed to do that?" reaction. Part
of that aesthetic appreciation for me originated with RSEXEC. Which
brings me to VFS and such.
Earlier in this thread Clem Cole observed:
On 6/23/2020 8:12 AM, Clem Cole wrote:
> That said, and to give the NFS team_a huge amount of credit _(and great
> applause), the VFS layer was better thought out than the FSS and in fact
> made it possible to add a lot of different file systems into UNIX
> later. FSS was much more ad hoc.
I think VFS and several related things are another instance of that
aesthetic appreciation. [I'm not claiming any credit, the initial NFS
work was just finishing up as I arrived at Sun. That work like that
happened there was part of why I wanted to be there and so I share
Clem's appreciation for the team.]
NFS could have been implemented by sprinkling "if (network)" statements
around a lot of code. A user or application program would not know any
differently had it been done that way. (Though they would over time as
the code became less maintainable with that implementation approach.)
That VFS has the qualities leading to Clem's applause is I think due to
a confluence of several things that likely hadn't occurred previously
and thus entitle it to claim "first" in response to the thread-starting
One of the motivators was the desire to have a network filing
abstraction, and to replace "nd" for diskless workstations among other
things. (That took a while, "nd" really hung on for various reasons.)
That's occurring in an environment of heterogeneity and "open systems"
thinking (which is a different thing from "open source"), and the desire
to be more "of the network" in the product offerings.
There was kind of a group-innate understanding that to be successful in
introducing these capabilities that they had to occur largely "behind"
the extant interfaces used by the nascent UNIX application market. To
some extent Sun's market success was based on being deliberately "more
vanilla than thou" with respect to APIs. The variations already extant
were a market-fragmenting influence and thus didn't need an additional
player doing more of it.
To be "of the network" made NFS a "file system for the Network (that
happens to look like UNIX)". The similarity and the known semantic
differences lead some to look at it as "it failed to do UNIX" but it's
not. The intent was "do the network, the network is NOT 'a' computer
(irony alert), the fallacies of networking apply and we resolve the
irreconcilable in favor of the network".
(An intangible factor relates to the group that Sun formed, talented
engineers, strikingly different people who shared good taste in design
and the desire to do the work to find the "simple" in a problem. A
different group of people with the same problem set wouldn't have
automatically gotten the same or even similar answer, sometimes it's
just in the air. Of course, a different group might have made an even
better answer, "innovation happens elsewhere" is more true than the
earlier-referenced layer of indirection principle.)
Sometimes (mostly even), good taste is expressed in framing the problem
appropriately. The "N" in NFS is deliberately not a "D". That's obvious
from the resulting definition but earlier in the effort it was a choice.
The intended distinction was that we weren't doing operating system work
in order to transcend the network by submerging it in the abstractions
of an OS. Rather, we wanted to build a network environment populated by
systems which were of a piece with it. While not codified until much
later, Deutsch's "Fallacies of Networking" were the controlling notions
in a lot of thinking and influenced things that at first wouldn't seem
to have anything to do with networking (e.g., msync()).
However, it would be wrong to say we realized enough at the time to
*know* that our goal was to build a system defined by a metric that it
avoid all of the networking fallacies. We knew some of it, were
incrementally hunting it, instincts were oriented that way. Had we been
a research organization that might have given rise to an initiative that
was more clearly defined. (But, I think we did a reasonable job of
pursuing the ideas while making products that people who weren't
thinking of such things bought. As it happens, a lot of FORTRAN users as
has been noted here before.
Regarding the earlier irony alert: to the extent that the evocative
marketing slogan of "The Network is the Computer" had any technical
underpinnings, it was an expression of this aim to design in favor of
the network. It isn't really irony so much as consequence.
The real irony is that when the slogan was first trotted out almost all
of the company but particularly engineering barfed at it. I recall the
marketing person(s) (individual contributors, not the executives later
claiming credit) trying to push it receiving huge rations of abuse. But
it stuck. And we came around once we looked beyond its technical
deficiency as a literal statement and saw it as evocative of what we had
been doing. They knew us better than we did. And, independent of any
technical matter, it worked really well. 'Find the simple" is a useful
admonition for marketing as well as engineering.
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