From 0e22e86348bb356e69ed28a58e959b7fab7c43cc Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Sun, 16 Oct 2011 14:26:40 -0400
Subject: [PATCH] Add support for subroot= option

Passing this option causes the initrd to chroot() into a subdirectory of /.
This is useful for parallel installing multiple systems in one filesystem.

This relies on a patched switch_root from util-linux.
---
 init                     |   32 +++++++++++++++++++++-----------
 scripts/init-bottom/udev |    5 ++---
 scripts/local            |    6 ++++--
 3 files changed, 27 insertions(+), 16 deletions(-)

diff --git a/init b/init
index 445c354..3ff2750 100755
--- a/init
+++ b/init
@@ -49,6 +49,8 @@ export init=/sbin/init
 export quiet=n
 export readonly=y
 export rootmnt=/root
+export subroot=
+export rootsubmnt=
 export debug=
 export panic=
 export blacklist=
@@ -68,6 +70,10 @@ for x in $(cat /proc/cmdline); do
 	init=*)
 		init=${x#init=}
 		;;
+	subroot=*)
+		subroot=${x#subroot=}
+		rootsubmnt=${x#subroot=}
+		;;
 	root=*)
 		ROOT=${x#root=}
 		case $ROOT in
@@ -218,14 +224,18 @@ maybe_break mountroot
 mountroot
 log_end_msg
 
+if test -n "${rootsubmnt}"; then
+	rootsubmnt=${rootmnt}/${rootsubmnt}
+fi
+
 maybe_break bottom
 [ "$quiet" != "y" ] && log_begin_msg "Running /scripts/init-bottom"
 run_scripts /scripts/init-bottom
 [ "$quiet" != "y" ] && log_end_msg
 
 # Preserve information on old systems without /run on the rootfs
-if [ -d ${rootmnt}/run ]; then
-	mount -n -o move /run ${rootmnt}/run
+if [ -d ${rootsubmnt}/run ]; then
+	mount -n -o move /run ${rootsubmnt}/run
 else
 	# The initramfs udev database must be migrated:
 	if [ -d /run/udev ] && [ ! -d /dev/.udev ]; then
@@ -239,27 +249,27 @@ else
 fi
 
 # Move virtual filesystems over to the real filesystem
-mount -n -o move /sys ${rootmnt}/sys
-mount -n -o move /proc ${rootmnt}/proc
+mount -n -o move /sys ${rootsubmnt}/sys
+mount -n -o move /proc ${rootsubmnt}/proc
 
 validate_init() {
 	checktarget="${1}"
 
 	# Work around absolute symlinks
-	if [ -d "${rootmnt}" ] && [ -h "${rootmnt}${checktarget}" ]; then
-		case $(readlink "${rootmnt}${checktarget}") in /*)
-			checktarget="$(chroot ${rootmnt} readlink ${checktarget})"
+	if [ -d "${rootsubmnt}" ] && [ -h "${rootsubmnt}${checktarget}" ]; then
+		case $(readlink "${rootsubmnt}${checktarget}") in /*)
+			checktarget="$(chroot ${rootsubmnt} readlink ${checktarget})"
 			;;
 		esac
 	fi
 
 	# Make sure the specified init can be executed
-	if [ ! -x "${rootmnt}${checktarget}" ]; then
+	if [ ! -x "${rootsubmnt}${checktarget}" ]; then
 		return 1
 	fi
 
 	# Upstart uses /etc/init as configuration directory :-/
-	if [ -d "${rootmnt}${checktarget}" ]; then
+	if [ -d "${rootsubmnt}${checktarget}" ]; then
 		return 1
 	fi
 }
@@ -273,7 +283,7 @@ if [ -n "${init}" ]; then
 fi
 
 # Common case: /sbin/init is present
-if [ ! -x "${rootmnt}/sbin/init" ]; then
+if [ ! -x "${rootsubmnt}/sbin/init" ]; then
 	# ... if it's not available search for valid init
 	if [ -z "${init}" ] ; then
 		for inittest in /sbin/init /etc/init /bin/init /bin/sh; do
@@ -315,5 +325,5 @@ unset resume
 unset resume_offset
 
 # Chain to real filesystem
-exec run-init ${rootmnt} ${init} "$@" <${rootmnt}/dev/console >${rootmnt}/dev/console
+exec switch_root --subroot ${subroot} ${rootmnt} ${init} "$@" <${rootsubmnt}/dev/console >${rootsubmnt}/dev/console
 panic "Could not execute run-init."
diff --git a/scripts/init-bottom/udev b/scripts/init-bottom/udev
index 375dfab..7922d0f 100755
--- a/scripts/init-bottom/udev
+++ b/scripts/init-bottom/udev
@@ -20,9 +20,8 @@ if [ -e /etc/udev/udev.conf ]; then
 fi
 
 # move the /dev tmpfs to the rootfs
-mount -n -o move /dev ${rootmnt}${udev_root}
+mount -n -o move /dev ${rootsubmnt}${udev_root}
 
 # create a temporary symlink to the final /dev for other initramfs scripts
 nuke /dev
-ln -s ${rootmnt}${udev_root} /dev
-
+ln -s ${rootsubmnt}${udev_root} /dev
diff --git a/scripts/local b/scripts/local
index 521e69a..25b518f 100644
--- a/scripts/local
+++ b/scripts/local
@@ -101,9 +101,11 @@ mountroot()
 	# FIXME This has no error checking
 	# Mount root
 	if [ "${FSTYPE}" != "unknown" ]; then
-		mount ${roflag} -t ${FSTYPE} ${ROOTFLAGS} ${ROOT} ${rootmnt}
+		echo mount ${roflag} -t ${FSTYPE} ${ROOTFLAGS} ${ROOT} ${rootmnt}
+		mount ${roflag} -t ${FSTYPE} ${ROOTFLAGS} ${ROOT} ${rootmnt} || echo "FAILED TO MOUNT ROOT"
 	else
-		mount ${roflag} ${ROOTFLAGS} ${ROOT} ${rootmnt}
+		echo mount ${roflag} ${ROOTFLAGS} ${ROOT} ${rootmnt}
+		mount ${roflag} ${ROOTFLAGS} ${ROOT} ${rootmnt} || echo "FAILED TO MOUNT ROOT"
 	fi
 
 	[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/local-bottom"
-- 
1.7.6.4