We changed the cpu protocol between editions.  The change was
to get rid of the second connection for notes.  This was a good
suggestion from Dave Mazieres at MIT.

You can convert the 2ed cpu.c to run on 3ed.  Here's the
diffs:

% diff cpu.c /sys/src/cmd/ocpu.c
21a22
> int	filter(int);
26a28
> int	fflag;
30,31c32,33
< char	*srvname = "cpu";
< char	*notesrv = "cpunote";
---
> char	*srvname = "ocpu";
> char	*notesrv = "ocpunote";
39a42
> int fdd;
50a54,56
> 	case 'f':
> 		fflag++;
> 		break;
109a116,118
> 	if(fflag)
> 		data = filter(data);
> 
124a134
> 	va_list arg;
126c136,138
< 	doprint(buf, buf+sizeof(buf), fmt, (&fmt+1));
---
> 	va_start(arg, fmt);
> 	doprint(buf, buf+sizeof(buf), fmt, arg);
> 	va_end(arg);
183a196
> 
185c198,202
< 	if(amount(fd, "/mnt/term", MREPL, "") < 0)
---
> 
> 	/* push fcall */
> 	if(fflag)
> 		fd = filter(fd);
> 	if(amount(fd, "/mnt/term", MCREATE|MREPL, "") < 0)
282a300
> 	char dir[4*NAMELEN];
285c303
< 	if((*fd = dial(na, 0, 0, 0)) < 0)
---
> 	if((*fd = dial(na, 0, dir, 0)) < 0)
288a307,308
> 	if(strstr(dir, "tcp"))
> 		fflag = 1;
318a339,366
> 
> /* Network on fd1, mount driver on fd0 */
> int
> filter(int fd)
> {
> 	int p[2];
> 
> 	if(pipe(p) < 0)
> 		fatal(1, "pipe");
> 
> 	switch(rfork(RFNOWAIT|RFPROC|RFFDG)) {
> 	case -1:
> 		fatal(1, "rfork record module");
> 	case 0:
> 		dup(fd, 1);
> 		close(fd);
> 		dup(p[0], 0);
> 		close(p[0]);
> 		close(p[1]);
> 		execl("/bin/aux/fcall", "fcall", 0);
> 		fatal(1, "exec record module");
> 	default:
> 		close(fd);
> 		close(p[0]);
> 	}
> 	return p[1];	
> }
> 

You also need to create the /rc/bin/service files on 3ed for
the 2ed ports:

% cat > /rc/bin/service/il17006 << EOF
#!/bin/rc
exec /bin/ocpu -R
EOF
% cat > /rc/bin/service/il17006 << EOF
#!/bin/ocpu -N
EOF
% cat > /rc/bin/service/tcp17005 << EOF
#!/bin/rc
exec /bin/ocpu -f -R
EOF
% cat > /rc/bin/service/tcp17006 << EOF
#!/bin/ocpu -N
EOF
% chmod +x /rc/bin/service/*1700[56]

You can then use ocpu to get back to 2ed.
I'll put these puppies in the next update.