[TUHS] environments/universes (was: Unix v6 problem with /tmp)

[clemc@ccc.com (Clem Cole)]

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​below​

On Thu, Jul 28, 2016 at 7:16 PM, Sven Mascheck <mascheck at in-ulm.de> wrote:

> On Wed, Jul 27, 2016 at 04:57:47PM -0400, Clem Cole wrote:
> > I created Conditionally Dependant Symlinks (CDSL) which I think only
> showed
> > up in Masscomp's RTU, Stellix and Tru64.   The were not only late
> binding,
> > but added the concept of a user settable context.   Very handy when
> trying
> > to create a "single system image" from multiple system.
>
> How did you implement it?
>

​Details are little fuzzy on some of the corner cases.  If I thought about
it, I bet they all come back.   But basically bit crumbs in the u_area
containing the "context" and then only trick was parsing the string in
nami/lookup, so you could have N actions depending on the value of the
context.     i.e.   path with embedded context string and grabbed another
special character (which if I recall we used the @ to deliminate followed
by a null then context1-> replacement1<null>context2->replacement2<null>
.... contextN->nth replacement<null>   which was originally linearly
searched since the original use (universes) had a small number of contexts.


When realized how useful they were @ LCC, and started to add support for
clusters and the node name became one of the contexts, we had to get a bit
smarter.   Tru64 and the unreleased HP-UX implementation did some hashing
and cleanup.  I've forgotten if that was done before or after the Intel
Paragon implementation.

BSD symlink semantics was then left alone, although I think I remember I
hacked the set/read code to handle the special char -- again IIR for set to
translate foo at bar to be foo@@bar and read the opposite.

Obviously you have a new failure of of the context did not match and an
open question of how to set/get the different contexts which varied.   For
universes
(which
​like Pyramid and others, Masscomp ​
RTU also
​provided
), my recollection
​ was
a new command hacked into the shells
​ and we had a general set/get variable services that predates the system
variable stuff of the BSDs and later Unix (that was modeled on VMS given
the Masscomp folks were sometimes ex-VMS kernel developers).

​
For the original work at LCC (which is what went into HP-UX and the Paragon
IIRC) , we had a new system service
​ for contexts and I've forgotten how that worked; but it was different
from the Masscomp or later BSD style scheme​
.

As for m​
y memory of Tru64
​ (which only used CDSL's for handling node dependant info)​;
 the node name was set independently
​ using yet another scheme (which I've now forgotten), but
was already in the u_area
​ so we could just look aside.​

Clem
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