[TUHS] V6 networking & alarm syscall

[Paul Ruizendaal]

I'm still happily experimenting with my combination of a V6 kernel with the 1981 tcp/ip stack from BBN, for example figuring out how one would write something like 'ping' using that API. That brought me to pondering the origins of the 'alarm()' sys call and how some things were done on the Spider network.

These are my observations:

1. First of all: I understand that early Unix version numbers and dates mostly refer to the manual editions, and that core users had more frequent snapshots of a constantly evolving code base.

2. If I read the TUHS archive correctly, alarm() apparently did not exist in the original V6 edition of mid-1975. On the same basis, it was definitely there by the time of the V7 edition of early '79 (with sleep() removed) - so alarm() would seem to have appeared somewhere in the '75-'78 time frame.

3. The network enhanced NCP Unix versions in the TUHS archive have alarm() appear next to sleep(). Although the surviving tapes date from '79, it would seem to suggest that alarm() may have originated in the earlier part of the '75-'78 time frame.

4. The Spider network file store program 'nfs' (source here: http://chiselapp.com/user/pnr/repository/Spider/dir?mtime=0&type=flat&udc=1&ci=tip) uses idioms like the below to avoid getting hung on a dead server/network:

	signal(14,timeout); alarm(30);
	if((read(fn,rply,100)) < 0) trouble();
	alarm(0);

The 'nfs' program certainly was available in the 5th edition, maybe even in the 4th edition (the surviving 4th edition source code includes a Spider device driver). However, the surviving source for 'nfs' is from 1979 as well, so it may include later additions to the original design.

5. Replacing sleep() with alarm() and a user space library routine seems to have happened only some time after alarm() appeared, so it would seem that this was an optimization that alarm() enabled, and not its raison d'être.

So here are some questions that the old hands may be able to shed some light on:

- When/where did alarm() appear? Was network programming driving its inception?

- Did Spider programs use a precursor to alarm() before that? (similar to V5 including 'snstat' in its libc - a precursor to ioctl).

Paul