Intruiging bits in the nsys kernel - TUHS

20 Jan 1999

In article by Eric Fischer:
...
  Congratulations on getting the nsys kernel running!  I
have
 a couple of random comments on what you posted to the list:

  Syscalls in `nsys' but not in V5:
 ---------------------------------
         1, &quit,                       /* 26 = quit */
         1, &intr,                       /* 27 = intr */
         1, &cemt,                       /* 29 = cemt */
         1, &ilgins,                     /* 33 = ilgins */
         1, &fpe,                        /* 40 = fpe */

                 These deliver signals QUIT, INTR, EMT, INS or FPE
                 to the pid in arg0. Any user can send these signals.  
 I think this is backwards -- these system calls don't deliver
 signals, they trap them.  That is, they're the predecessors
 of signal(), not kill(). 
Eric is quite correct, and I realised this after reading some comments
on the V2 kernel. The nsys kernel also has a sig() system call which
allows a process to trap an arbitrary signal. This is why the syscalls
above were removed: there was a more general system call available.

...

  Syscalls in V5 but not in `nsys':
 ---------------------------------
         0, &getpid,                     /* 20 = getpid */
         1, &smdate,                     /* 30 = smdate */
         0, &nice,                       /* 34 = nice */
         0, &pipe,                       /* 42 = pipe */		!!!
         4, &profil,                     /* 44 = prof */  
 This part seems really weird.  Since it has fpe() but not nice() and
 pipe(), that would have to mean it's somewhere intermediate between
 v2 and v3, at least if the details in Doug McIlroy's "Research Unix
 Reader" are all accurate.  And I *really* don't understand why there
 would be space reserved in the system call table for nice and pipe
 but no implementations of the functions.

 The other weird part is that McIlroy says that smdate() was in v1
 through v3 but disappeared after that.  I don't have the v5 kernel
 source at hand right now, so I can't check up on that, but it's
 strange that smdate should be missing here if this is an early v3.

 Actually, on further inspection this must be a *late* v3, since it
 has mknod(), getgid(), and setgid(), which aren't supposed to have
 shown up until v4.  (No signal(), though, so it's not quite v4.)
 That's still very odd that pipes would be left out, unless this
 version was crunched to run in an especially small memory or something.

 And yet, v3 was supposed to have been released in February, 1973, and
 this is earlier than that, so what are any v4 features doing there at
 all?  This just gets stranger and stranger...
 eric 
I've had some chat with Dennis about this kernel, and how it fitted into
development. The summary is: Ken tried to rewrite the assembly version of
the kernel in B (or NB) in 1972, but gave up because structures didn't
exist. Once B -> NB -> C and got structures, they tried again. Apparently,
the `new' kernel (aka nsys) was developed in parallel with the `old' 
assembly kernel during early to mid-1973. Then, Dennis says:

	I'm pretty sure that we didn't adopt [the C version of the kernel]
	as the standard "production" system until about September 1973.
	It is very likely that the real "sys" was still in assembler.
	Pipes were probably added first to [the sys] version, given the
	evidence in "nsys."

Dennis also says:

	During 1972, Ken finally puts pipes into Unix at McIlroy's urging.

which would explain why there is a reserved syscall in `nsys', but no
code as yet.

I can't explain the existence of the mknod(), getgid(), and setgid()
system calls. Norman and Bob Keys, I think one/both of you have got the
old manuals, can you look through them and find out when these syscalls
appeared?

Cheers all,
	Warren

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 From Warren Toomey &lt;wkt(a)henry.cs.adfa.edu.au&gt; Wed
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Subject: Old pic of ken and dmr
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Date: Wed, 20 Jan 1999 14:46:41 +1100 (EST)
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All,
	Patrick Regan, from Bell Labs, has sent in a 2M jpg of
Ken and Dennis at the console of a PDP-11/20, around 1970. It's at:

http://minnie.cs.adfa.edu.au/PUPS/Images/ken-and-den.jpg

Ciao,
	Warren

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