using Vax as fileserver for Xerox Lisp machine

[Charles Root]

We think Xerox is still not very close to being able to remove PUP
support.  From the user's point of view, PUP is much more useful than
you suggest.  First, I don't know what you mean when you say it is
vanishing from 4.3.  It wasn't in 4.2 to begin with.  PUP is
distributed separately from 4.2, as a set of modifications that have
to be added.  It consists of a set of user-level code, a device
driver, and a couple of very small hooks in the Ethernet device
driver.  It was carefully designed to be as separate as possible from
the rest of the kernel.  I find it hard to believe that 4.3 is doing
anything that would make it impossible to install the modifications.
I realize that 4.2 has some modules that seems to be related to PUP.
These modules are not used by the actual PUP implementation, so their
removal would not cause any problem.  The PUP implementation uses
/dev/enet, which is a general-purpose Ethernet packet filter.  It
allows the user to specify tests that define what packets he is
interested in seeing.  Thus it can be used to implement any protocol.
In fact, we use it here to implement PUP, PUP Arp, Internet Reverse
ARP, and a small subset of XNS (nothing exciting, just time of day and
telling Interlisp workstations what their PUP host number is).  The
hook into the kernel effectively reorganizes the switch statement in
the packet-input routine so that any packet not otherwise recognized
is sent to the /dev/enet driver for processing.

Second, as far as I know, PUP is the only protocol currently used by
Interlisp that supports random access.  This means that TCP/IP is not
a replacement for it.  Unless something has changed recently, XNS
isn't either.  

Third, even if XNS were a replacement, sites such as ours would need a
portable implementation of an XNS file server on Unix.  I note that
this is still absent from the list of XNS support you gave.  In order
for us to use it, we would have to be able to port it to the Pyramid
90x.  The XNS situation is certainly getting better as time goes on,
but at the moment Xerox has not done what is necessary to replace PUP
with XNS.  We know that this is a goal, but we trust that they will
not be sufficiently suicidal to remove PUP from Interlisp before all
of their customers are able to replace its functionality with
something else.  What I am hoping for is a file server protocol that
supports random access and runs on top of TCP/IP.  The PUP file server
protocol (LEAF) runs on top of PUP's equivalent of UDP.  It could
probably be moved to work on top of UDP without too much trouble.