#!/bin/sh
#
# /sbin/init
#
# This init script can be run from an inittar (or initrd) to boot a system
# in the traditional way (i.e. with root=/dev/...)
#
# It loads all required modules (see /etc/load-modules for explanation),
# optionally executes /etc/rc, mounts the fileystem given by $root or in
# /proc/sys/kernel/real-root-dev, exchanges the current root (tmpfs or
# ramdisk) with $root using pivot_root(8) and chroot(8).
#
# Filesystem situation before pivot_root/chroot:
#
# tmpfs		tmpfs	/
# $root		any	$new_root
#
# Situation right after pivot_root/chroot:
#
# $root		any	/
# tmpfs		tmpfs	$old_root
#
# where $new_root and $old_root are /mnt per default (on different fileystems,
# of course).
#
# If the kernel starts with a premounted devfs, the script also mounts
# a devfs on $root and unmounts the devfs on the tmpfs.
#
# Note that you still have to unmount $old_root from within /sbin/init on the
# new rootfs.
#
# Matthias Kilian <kili@outback.escape.de>, 30.11.2001
#
# TODO:
# - pass additional command line arguments to the "real" /sbin/init
# - include fancy things like fsck'ing the real root device.

version=0.9.1

PATH=/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin
export PATH

# Just a simple echo with RDINIT prefix:
say() {
	echo -n "RDINIT: "
	echo "$@"
}

# Who the hell is general failure?
fail() {
	say "Error: $*" >& 2
	say Giving up, dropping you into a shell. Good luck!
	# May be someone wants to check what happened...
	exec /bin/sh -i
}

# Should this script exit (for whatever reason), give an error message and
# start a shell
trap "fail exit." 0


# Some configuration for used mountpoints
# $new_root is the mountpoint on tmpfs used for mounting the new rootfs.
new_root=mnt

# $mntpts contains a space separated list of other valid mountpoints on
# $new_root used for the tmpfs
mntpts="mnt newroot new-root"

# Special mountpoint. If it exists on $new_root, the tmpfs will stay here
# after the pivot_root, and it will *not* be unmounted.
keep_mntpt=initfs


say "initrd/inittar bootup script, version $version"
say "2001, Matthias Kilian"
say "args: $*"
say "press RETURN within 5 seconds to get an interactive shell"

( trap "exit 1" 15; sh -c '( sleep 5 && kill $$ )& read _' ) > /dev/null 2>&1 &&
exec /bin/sh -i

# Run /etc/rc, if it exists
if [ -x /etc/rc ]; then
	say run /etc/rc
	/etc/rc
else
	# Load modules
	say load modules
	/etc/load-modules || fail /etc/load-modules
fi


# mount /proc
test -d /proc || mkdir /proc || fail mkdir /proc
test -e /proc/mounts || mount -t proc proc /proc ||
	fail mount -t proc proc /proc

# check for devfs
unset usedevfs
while read dev dir fstype _; do
	if [ "$dir" = /dev -a "$fstype" = devfs ]; then
		say "there's a devfs mounted"
		usedevfs=y
		break
	fi
done < /proc/mounts

# Mount new root filesystem, given in $root or in
# /proc/sys/kernel/real-root-dev.
if [ -z "$root" ]; then
	rrd=/proc/sys/kernel/real-root-dev
	say root not set, looking up $rrd
	if [ -r "$rrd" ]; then
		mm=$(cat "$rrd") || fail cannot read $rrd
		major=$(($mm / 256)) || fail "major=$(($mm / 256))"
		minor=$(($mm % 256)) || fail "minor=$(($mm % 256))"
		say found "$major:$minor, creating /dev/root"
		root=/dev/root
		mknod $root b $major $minor || fail mknod $root b $major $minor
	else
		fail $rrd does not exist
	fi
fi


test -d /$new_root || mkdir /$new_root || fail mkdir /$new_root
say mounting $root
mount -r $root /$new_root || fail mount $root /$new_root

# If we've devfs mounted, mount it on the new root, too
if [ "$usedevfs" = y ]; then
	say mount devfs on new rootfs
	mount -t devfs none /$new_root/dev ||
		fail mount -t devfs none /$new_root/dev
fi


# Redirect stdin, stdout and stderr to /dev/console on the *new* root
# fs. Without this redirection, it would impossible to unmount
# $old_root later.
say redirect stdin, stdout and stderr to console on /$new_root
console=/$new_root/dev/console
exec < $console > $console 2>&1 || fail redirection

# Now, unmount devfs on initfs
if [ "$usedevfs" = y ]; then
	say unmount devfs from initfs
	umount /dev || fail umount /dev
fi

umount /proc || fail umount /proc

cd /$new_root || fail cd /$new_root

# Check for a valid mountpoint.
say -n searching a mountpoint for initfs...
for mp in $keep_mntpt $mntpts; do
	echo -n " $mp"
	test -d $mp && old_root=$mp && break
done
echo
test -n "$old_root" || fail no valid mountpoint found
say mountpoint for initfs: $old_root

if [ "$old_root" != "$keep_mntpt" ]; then
	:> /.dontkeep
fi

# Exchange current and new root filesystem, leaving current
# filesystem in $old_root.
say swap initfs and rootfs
pivot_root . $old_root || fail pivot_root . $old_root


# Some preparation on the new root filesystem. Finally, the *real*
# /sbin/init is launched.
say chroot to new rootfs
exec chroot .  /bin/sh <<- EOF
	if [ -e /$old_root/.dontkeep ]; then
	    echo RDINIT: umount /$old_root
	    umount /$old_root > /dev/null 2>&1 ||
	    echo RDINIT: Error: could not unmount /$old_root
	fi
	echo INIT: starting /sbin/init "$@"
	exec /sbin/init "$@"
EOF


# Should't happen
fail either the inittar is broken or /sbin/init is missing.