[hacktree] Add documentation for parallel-debian

[Colin Walters <walters src gnome org>]

commit 8020f444cf7bbc936be9e45670401e641e297d36
Author: Colin Walters <walters verbum org>
Date:   Mon Oct 17 09:40:12 2011 -0400

    Add documentation for parallel-debian

 README-testing-multiroot.md                        |   38 -----
 .../0001-Add-support-for-subroot-option.patch      |  148 ++++++++++++++++++++
 .../0001-switch_root-Add-subroot-option.patch      |  102 ++++++++++++++
 parallel-debian/README-testing-multiroot.md        |   80 +++++++++++
 parallel-debian/create-wheezy-image.sh             |   16 ++
 parallel-debian/make-image-parallel.sh             |   20 +++
 6 files changed, 366 insertions(+), 38 deletions(-)
---
diff --git a/parallel-debian/0001-Add-support-for-subroot-option.patch b/parallel-debian/0001-Add-support-for-subroot-option.patch
new file mode 100644
index 0000000..5abf7c7
--- /dev/null
+++ b/parallel-debian/0001-Add-support-for-subroot-option.patch
@@ -0,0 +1,148 @@
+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
+
diff --git a/parallel-debian/0001-switch_root-Add-subroot-option.patch b/parallel-debian/0001-switch_root-Add-subroot-option.patch
new file mode 100644
index 0000000..145ee70
--- /dev/null
+++ b/parallel-debian/0001-switch_root-Add-subroot-option.patch
@@ -0,0 +1,102 @@
+From fa0e7df4e3d6550f0391bb3b81b2b6ac5165439d Mon Sep 17 00:00:00 2001
+From: Colin Walters <walters verbum org>
+Date: Sun, 16 Oct 2011 21:01:46 -0400
+Subject: [PATCH] switch_root: Add --subroot option
+
+This is useful for parallel installing multiple operating system
+roots.  See: http://git.gnome.org/browse/hacktree
+---
+ sys-utils/switch_root.8 |    4 ++++
+ sys-utils/switch_root.c |   31 +++++++++++++++++++++----------
+ 2 files changed, 25 insertions(+), 10 deletions(-)
+
+diff --git a/sys-utils/switch_root.8 b/sys-utils/switch_root.8
+index 34ab0d0..6981852 100644
+--- a/sys-utils/switch_root.8
++++ b/sys-utils/switch_root.8
+@@ -27,6 +27,10 @@ process.
+ show help and exit
+ .IP "\fB\-V, \-\-version\fP"
+ show version number and exit
++.IP "\-\-subroot\fP"
++Instead of calling chroot into the / of the new root, instead use the
++given argument.  This helps parallel install multiple operating systems in one
++root filesystem.
+ 
+ .SH RETURN VALUE
+ .B switch_root
+diff --git a/sys-utils/switch_root.c b/sys-utils/switch_root.c
+index 2dfed71..20ae5d6 100644
+--- a/sys-utils/switch_root.c
++++ b/sys-utils/switch_root.c
+@@ -108,7 +108,7 @@ done:
+ 	return rc;
+ }
+ 
+-static int switchroot(const char *newroot)
++static int switchroot(const char *newroot, const char *subroot)
+ {
+ 	/*  Don't try to unmount the old "/", there's no way to do it. */
+ 	const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
+@@ -141,7 +141,7 @@ static int switchroot(const char *newroot)
+ 		return -1;
+ 	}
+ 
+-	if (chroot(".")) {
++	if (chroot(subroot ? subroot : ".")) {
+ 		warn("failed to change root");
+ 		return -1;
+ 	}
+@@ -160,7 +160,7 @@ static int switchroot(const char *newroot)
+ 
+ static void usage(FILE *output)
+ {
+-	fprintf(output, "usage: %s <newrootdir> <init> <args to init>\n",
++	fprintf(output, "usage: %s [--subroot DIR] <newrootdir> <init> <args to init>\n",
+ 			program_invocation_short_name);
+ 	exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
+ }
+@@ -175,22 +175,33 @@ static void version(void)
+ int main(int argc, char *argv[])
+ {
+ 	char *newroot, *init, **initargs;
++	char *subroot = NULL;
++	int argi;
+ 
+-	if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
++	if (argc < 2)
++		usage(stderr);
++
++	argi = 1;
++	if ((!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
+ 		usage(stdout);
+-	if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V")))
++	if ((!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V")))
+ 		version();
+-	if (argc < 3)
++	if (argc > 3 && argv[1] && (!strcmp(argv[1], "--subroot"))) { 
++		subroot = argv[2];
++		argi = 3;
++	}
++	if (argc <= argi+1) {
+ 		usage(stderr);
++	}
+ 
+-	newroot = argv[1];
+-	init = argv[2];
+-	initargs = &argv[2];
++	newroot = argv[argi];
++	init = argv[argi+1];
++	initargs = &argv[argi+1];
+ 
+ 	if (!*newroot || !*init)
+ 		usage(stderr);
+ 
+-	if (switchroot(newroot))
++	if (switchroot(newroot, subroot))
+ 		errx(EXIT_FAILURE, "failed. Sorry.");
+ 
+ 	if (access(init, X_OK))
+-- 
+1.7.6.4
+
diff --git a/parallel-debian/README-testing-multiroot.md b/parallel-debian/README-testing-multiroot.md
new file mode 100644
index 0000000..8c0a134
--- /dev/null
+++ b/parallel-debian/README-testing-multiroot.md
@@ -0,0 +1,80 @@
+
+Experimenting with multiple roots
+---------------------------------
+
+<http://wiki.debian.org/QEMU#Setting_up_a_testing.2BAC8-unstable_system>
+
+Follow the steps for making a disk image, downloading the business
+card CD, booting it in QEMU and running through the installer.
+
+Test that the image works after installation too, before you start
+modifying things below!  Remember to remove the -cdrom and -boot
+options from the installation QEMU command.
+
+Modifying the image
+-------------------
+
+You now have a disk image in debian.img, and the first partition
+should be ext4.
+
+The first thing I did was mount the image, and move almost everythig
+(/boot, /var, /etc), except lost+found to a new directory "r0".
+
+	$ mkdir /mnt/debian
+	$ modprobe nbd max_part=8
+	$ qemu-nbd --connect=/dev/nbd0 debian.qcow
+	$ mount /dev/nbd0p1 /mnt/debian/
+	$ cd /mnt/debian
+	$ mkdir r0
+	$ DIRS="bin boot dev etc lib lib64 media mnt opt proc root run sbin selinux srv sys tmp usr var"
+	$ mv $DIRS r0 
+
+Now with it still mounted, we need to move on to the next part -
+modifying the initrd.  
+
+Then I started hacking on the initrd, making understand how to chroot
+to "r0".  I ended up with two patches - one to util-linux, and one to
+the "init" script in Debian's initrd.
+
+See:
+    0001-switch_root-Add-subroot-option.patch
+    0001-Add-support-for-subroot-option.patch
+
+$ git clone --depth=1 git://github.com/karelzak/util-linux.git
+$ cd util-linux
+$ patch -p1 -i ../0001-switch_root-Add-subroot-option.patch
+$ ./autogen.sh; ./configure ; make
+
+Now you have a modified "sys-utils/switch_root" binary.  Let's next
+patch the initrd and rebuild it:
+
+Make a backup:
+
+	$ mkdir initrd
+	$ cp /mnt/debian/boot/initrd.img-3.0.0-1-amd64{,.orig}
+
+Unpack, and patch:
+
+	$ zcat /mnt/debian/boot/initrd.img-3.0.0-1-amd64 | (cd initrd; cpio -d -i -v)
+	$ (cd initrd && patch -p1 -i ../0001-Add-support-for-subroot-option.patch)
+
+Repack:
+
+	$ (cd initrd; find | cpio -o -H newc) | gzip > /mnt/debian/boot/initrd.img-3.0.0-1-amd64.new
+	$ mv /mnt/debian/boot/initrd.img-3.0.0-1-amd64{.new,}
+
+Running hacktree inside the system
+----------------------------------
+
+This means that after booting, every process would be in /r0 -
+including any hacktree process.  Assuming objects live in say
+/objects, we need some way for hacktree to switch things.  I think
+just chroot breakout would work.  This has the advantage the daemon
+can continue to use libraries from the active host.
+
+Note there is a self-reference here (as is present in Debian/Fedora
+etc.) - the update system would at present be shipped with the system
+itself.  Should they be independent?  That has advantages and
+disadvantages.  I think we should just try really really hard to avoid
+breaking hacktree in updates.
+
diff --git a/parallel-debian/create-wheezy-image.sh b/parallel-debian/create-wheezy-image.sh
new file mode 100755
index 0000000..6f8263a
--- /dev/null
+++ b/parallel-debian/create-wheezy-image.sh
@@ -0,0 +1,16 @@
+#!/bin/sh
+
+set -e
+set -x
+
+if test -f debian.img; then
+  echo debian.img already exists
+  exit 1
+fi
+
+qemu-img create debian.img 600M
+mkfs.ext2 -q -F debian.img
+mkdir -p debian-mnt
+mount -o loop debian.img debian-mnt
+debootstrap --arch amd64 wheezy debian-mnt
+umount debian-mnt
diff --git a/parallel-debian/make-image-parallel.sh b/parallel-debian/make-image-parallel.sh
new file mode 100755
index 0000000..b6aaa9e
--- /dev/null
+++ b/parallel-debian/make-image-parallel.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+
+set -e
+set -x
+
+DIRS="bin boot dev etc lib lib64 media mnt opt proc root run sbin selinux srv sys tmp usr var"
+
+if ! test -f debian.img; then
+  echo need debian.img
+  exit 1
+fi
+
+mount -o loop debian.img debian-mnt
+cd debian-mnt
+if ! test -d r0; then
+  mkdir r0
+  mv $DIRS r0
+fi
+cd ..
+umount debian-mnt