In Mid December 2002, a new feature was added to the system. It changes the previous #//boot to be a directory rather than a file, and allows what used to be a binary that had to be compiled to be a script instead.

Russ Cox said something like this in http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&selm=606456fcdc17ce997666a1895d86f9ba%40plan9.bell-labs.com

There is a new kernel config file section called "bootdir" that lists the files to be placed in #//boot. There are no binaries in #/ itself anymore.

A typical bootdir section might look like

	bootdir
		bootpcdisk.out boot
		/386/bin/ip/ipconfig
		/386/bin/auth/factotum
		/386/bin/disk/kfs
		/386/bin/cfs

which says that /boot will contain four files: boot, ipconfig, factotum, kfs, and cfs, copied from the listed paths.

The kernels have always special cased boot$CONF.out to get it listed as /boot. It is now /boot/boot, and no longer a special case.

Now that everything is in /boot, initcode had to change for all the kernels; /boot/boot itself had to change to exec /boot/ipconfig (instead of /ipconfig), etc. Finally, auth_getkey changed. It looks for /factotum and then /boot/factotum, to deal with either type of kernel.

The boot file /386/bin/ip/ipconfig (e.g.) turns into _386_bin_ip_ipconfig.root.s and then _386_bin_ip_ipconfig.root.8. It's a bit of an ugly name, but mk clean will get rid of them. You could imagine just using the last path element, but that might lead to weird build inconsistencies if kernels were using two different files with the same last element. One unfortunate consequence of the big name is that _386_bin_auth_factotum.root.s is too long for the current file servers to deal with. You could use lnfs to get around this, but I didn't want to require lnfs(4) for the kernel build, so we have a rule in portmkfile that copies factotum and ipconfig to factotum.hack and ipconfig.hack and then the bootdir section actually looks like:

	bootdir
		bootpcdisk.out boot
		ipconfig.hack ipconfig
		factotum.hack factotum
		/386/bin/disk/kfs
		/386/bin/cfs

sadly. That will go away when we get long file names.

The pc initcode is also changed. Whereas before it used to do

	exec("/boot", ["boot", 0]);

in hand-coded assembly (pc/initcode.s), it now does

	open("#c/cons", OREAD);
	open("#c/cons", OWRITE);
	open("#c/cons", OWRITE);
	bind("#c", "/dev", MAFTER);
	bind("#ec", "/env", MAFTER);
	bind("#e", "/env", MCREATE|MAFTER);
	bind("#s", "/srv", MREPL|MCREATE);
	execl("/boot/boot", "/boot/boot", 0);

in C (port/initcode.c). The point is to set up enough of a namespace that /boot/boot can be a shell script. Eventually the other architectures should change too, though it's not urgent. If someone wants to do the bitsy, send me mail and I'll let you know what it took to get one of the old undistributed mips kernels changed over. (The compiler setup is similar.)

As a much bigger example, I built a kernel called pcext the other night. It uses rx and trampoline to connect through a Plan 9 gateway machine to the root file server. It uses this bootdir:

	bootdir
		bootext boot
		/386/bin/rc
		/rc/lib/rcmain
		/386/bin/bind
		/386/bin/cat
		/386/bin/cp
		/386/bin/echo
		/386/bin/mount
		/386/bin/sleep
		factotum.hack factotum
		/386/bin/ip/ipconfig
		/386/bin/cfs
		/386/bin/aux/srvthru

(and does require lnfs to build).

Srvthru is the obvious program -- it connects to rx, authenticates, starts trampoline to the real file server, and then optionally pushes cfs onto the connection.

The point is that bootext is a shell script, which makes it easier to tweak than when /boot was a binary building out of /sys/src/9/boot.

	#!/boot/rc -m /boot/rcmain
	
	cd /boot
	cp '#r/rtc' '#c/time'
	bind -a /boot /bin
	bind -a '#I' /net
	bind -a '#l0' /net
	bind -a '#S' /dev
	bind '#p' /proc
	bind '#d' /fd
	bind -a /boot /
	ipconfig
	echo 'authdom=cs.bell-labs.com auth=204.178.31.3' >>/net/ndb
	factotum -sfactotum -u -a 204.178.31.3
	cargs=()
	if(~ $#cfs 1 && ! ~ $cfs off)
		cargs=(-c $cfs)
	srvthru $cargs tcp!204.178.31.2!17009 il!emelie!9fs boot emelie
	mount -c /srv/boot /root
	bind -ac /root /
	bind -c /root/mnt /mnt
	mount -a '#s/factotum' /mnt
	rootdir=/root
	rootspec=''
	/386/init -t
	/boot/rc -m/boot/rcmain -i	# in case init fails

It takes care of everything /boot traditionally does, using srvthru as the way to establish /srv/boot (and also /srv/emelie, just for kicks).