Here are the details on Dennis Ritchie's Plan 9 plug-in to read the s2-bits
tape, as sent in by e-mail.

From: dmr@plan9.bell-labs.com
Subject: Re: Happy New Year + 1stEd binaries run again
Date: Tue, 4 Jan 2000 22:19:01 -0500
To: wkt@cs.adfa.edu.au
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Status: RO

Attached below is  the "plugin" for tapfs (part of the plan 9 things that
mount things as file systems).  It's the only part that's tap-specific.

Just got your latest mail--as I said, I don't recognize the format of s1
either.  My headers for s2 are consistent with yours, I think, modulo
date understanding.  (And mapping of permissions etc into Plan 9).
For example: 

--r---wxrw- M 10745 79524 28 1912 Jan  3  1973 bin/form

The M 10745 79524 28 part is just Plan 9; there's a possible year
ambiguity; the day difference is probably US vs AU.

	---

#include <u.h>
#include <libc.h>
#include "tapefs.h"

/*
 * File system for old tap tapes.
 */

struct tap {
	unsigned char	name[32];
	unsigned char	mode[1];
	unsigned char	uid[1];
	unsigned char	size[2];
	unsigned char	tmod[4];
	unsigned char	taddress[2];
	unsigned char	unused[20];
	unsigned char	checksum[2];
} dir[192];

int	tapefile;
char	buffer[8192];
long	cvtime(unsigned char *);

void
populate(char *name)
{
	int i, isabs;
	struct tap *tpp;
	Fileinf f;

	replete = 1;
	tapefile = open(name, OREAD);
	if (tapefile<0)
		error("Can't open argument file");
	read(tapefile, dir, sizeof dir);
	for (i=0, tpp=&dir[8]; i<192; i++, tpp++) {
		unsigned char *sp = (unsigned char *)tpp;
		int j, cksum = 0;
		for (j=0; j<32; j++, sp+=2)
			cksum += sp[0] + (sp[1]<<8);
		cksum &= 0xFFFF;
		if (cksum!=0) {
			print("cksum failure\n");
			continue;
		}
		if (tpp->name[0]=='\0')
			continue;
		f.addr = (void *)(tpp->taddress[0] + (tpp->taddress[1]<<8));
		if (f.addr==0)
			continue;
		f.size = tpp->size[0] + (tpp->size[1]<<8);
		f.mdate = cvtime(tpp->tmod);
		f.mode = tpp->mode[0]&0777;
		isabs = tpp->name[0]=='/';
		f.name = (char *)tpp->name+isabs;
		poppath(f, 1);
	}
}

long
cvtime(unsigned char *tp)
{
	unsigned long t = (tp[1]<<24)+(tp[0]<<16)+(tp[3]<<8)+(tp[2]<<0);
	t /= 60;
	t += 3*365*24*3600;
	return t;
}

void
popdir(Ram *r)
{
	USED(r);
}

void
dotrunc(Ram *r)
{
	USED(r);
}

void
docreate(Ram *r)
{
	USED(r);
}

char *
doread(Ram *r, long off, long cnt)
{
	if (cnt>sizeof(buffer))
		print("count too big\n");
	seek(tapefile, 512*(int)r->data+off, 0);
	read(tapefile, buffer, cnt);
	return buffer;
}

void
dowrite(Ram *r, char *buf, long off, long cnt)
{
	USED(r); USED(buf); USED(off); USED(cnt);
}

int
dopermw(Ram *r)
{
	USED(r);
	return 0;
}