tar2fs

#!/bin/bash -ex
# usage:
# tar2fs chroot.tar image.raw [size_in_bytes [fstype]]

. shell-error

if [ $# -lt 2 ]; then
	fatal "error: tar2fs needs at least two arguments"
fi

# this needs env_keep sudo setup to actually work
if [ -n "$GLOBAL_BUILDDIR" ]; then
	WORKDIR="$GLOBAL_BUILDDIR/vmroot"
else
	WORKDIR="$(mktemp --tmpdir -d vmroot-XXXXX)"
fi

[ -n "$WORKDIR" ] || fatal "couldn't come up with suitable WORKDIR"

[ -n "$GLOBAL_DEBUG" ] || message "WORKDIR: $WORKDIR"

MB=1048576		# a parted's "megabyte" in bytes is *broken*
SIZE_FACTOR=2		# multiply the sizes found by this value

CUR_BOUNDARY=0		# align first partition at 1MB for performance (+1)

INITRD_MODULES=
BOOTFSTYPE=
BOOTPART=

case "`arch`" in	# NB: sudo => no GLOBAL_ will do either; mind qemu-*
*86*)
	# NB: different storage modules might be needed for non-kvm
	INITRD_MODULES="sd_mod ata_piix"
	BLOCKDEV="/dev/sda"	# might be /dev/vda for virtio
	ROOTPART="1"
	;;
arm*)
	BOOTFSTYPE="ext2"	# support expected in every sane target uboot
	BLOCKDEV="/dev/mmcblk0p"	# ...hopefully...
	BOOTPART="1"
	ROOTPART="2"
	;;
esac

# figure out the part taken by /boot in the given tarball
boot_size() {
	if [ -n "$BOOTPART" ]; then
		tar tvf "$1" \
		| awk ' \
			BEGIN { sum=0 }
			/^-.* \.\/boot\// { sum=sum+$3 }
			END { print sum }'
	else
		echo "0"
	fi
}

# parted wrapper for convenience
parting() { parted "$LOOPDEV" --align optimal --script -- "$@"; }

# unfortunately parted is insane enough to lump alignment controls
# into unit controls so creating adjacent partitions sized in MiB
# is not as straightforward as it might be... thus "+1" padding;
# see also http://www.gnu.org/software/parted/manual/parted.html#unit
mkpart() {
	# a bit different start/end semantics to handle end of device too
	local start="$(($CUR_BOUNDARY + 1))"	# yes, we lose a megabyte
	if [ -n "$1" ]; then
		CUR_BOUNDARY="$(($start + $1))"
		local end="$CUR_BOUNDARY"MiB
	else
		local end="-1s"	# last sector of the image
	fi
	parting mkpart primary ext2 "$start"MiB "$end"
}

# a tarball containing chroot with a kernel
TAR="$1"
[ -s "$TAR" ] || fatal "source tarball doesn't really exist"

# a path to the image to be generated
IMG="$2"
[ -d "$(dirname "$IMG")" ] || fatal "target directory doesn't exist"

# 0 means auto; if a value is specified it holds (no /boot subtracted)
ROOTSIZE="$3"
[ -n "$ROOTSIZE" -a "$ROOTSIZE" != 0 ] || unset ROOTSIZE

# image size in bytes (note the final ceil rounding to megabytes)
TARSIZE="$(stat -Lc %s "$TAR")"
# /boot size in that tarball
BOOTSIZE="$(boot_size "$TAR")"
DEFSIZE="$(($SIZE_FACTOR * ($TARSIZE - $BOOTSIZE)))"	# (exact sizes)
ROOTSIZE="$((${ROOTSIZE:-$DEFSIZE} + $MB - 1))"
# image and /boot sizes in megabytes
ROOTSIZEM="$(($ROOTSIZE / $MB))"
BOOTSIZEM="$((($SIZE_FACTOR * $BOOTSIZE + $MB - 1) / $MB))"

# tested to work: ext[234], jfs
# NB: xfs doesn't have a spare sector for the bootloader
ROOTFSTYPE="${4:-ext4}"

# single root partition hardwired so far,
# add another image for home/data/swap if needed
ROOTDEV="$BLOCKDEV$ROOTPART"

# last preparations...
MKFS="mkfs.$ROOTFSTYPE ${BOOTFSTYPE:+mkfs.$BOOTFSTYPE}"
for i in losetup sfdisk parted kpartx $MKFS; do
	if ! type -t "$i" >&/dev/null; then
		fatal "$i required but not found in host system"
	fi
done

LOOPDEV="$(losetup --find)"	# would be sad about non-binary megabytes too
ROOTFS="$WORKDIR/chroot"

BOOTFS=
if [ -n "$BOOTPART" ]; then
	BOOTFS="$ROOTFS/boot"
fi

exit_handler() {
	rc=$?
	if [ -n "$ROOTFS" ]; then
		umount ${BOOTFS:+"$BOOTFS"} "$ROOTFS"{/dev,/proc,/sys,}

		if [ -n "$LOOPDEV" ]; then
			kpartx -d "$LOOPDEV"
			losetup --detach "$LOOPDEV"
		fi
		rm -r -- "$ROOTFS"
		rmdir -- "$WORKDIR"
	fi
	exit $rc
}

# handle -e in shebang as well
trap exit_handler EXIT ERR

# prepare disk image and a filesystem inside it
rm -f -- "$IMG"
OFFSET="$(($CUR_BOUNDARY + $BOOTSIZEM + $ROOTSIZEM - 1))"
dd if=/dev/zero of="$IMG" conv=notrunc bs=$MB count=1 seek="$OFFSET"
losetup "$LOOPDEV" "$IMG"

parting mklabel msdos

if [ -n "$BOOTPART" ]; then
	BOOTDEV="$BLOCKDEV$BOOTPART"
	mkpart "$BOOTSIZEM"
fi

# not ROOTSIZEM but "the rest"; somewhat non-trivial arithmetics lurk in parted
mkpart

kpartx -a "$LOOPDEV"
LOOPROOT="/dev/mapper/$(basename "$LOOPDEV")p$ROOTPART"

# might take a tiny bit of time to actually appear
for i in `seq 10`; do
	[ -b "$LOOPROOT" ] && break || sleep 0.1
done

mkfs."$ROOTFSTYPE" "$LOOPROOT"

if [ -n "$BOOTPART" ]; then
	LOOPBOOT="/dev/mapper/$(basename "$LOOPDEV")p$BOOTPART"
	mkfs."$BOOTFSTYPE" "$LOOPBOOT"
fi

# mount and populate it
mkdir -pm755 "$ROOTFS"
mount "$LOOPROOT" "$ROOTFS"

if [ -n "$BOOTPART" ]; then
	mkdir -pm700 "$BOOTFS"
	mount "$LOOPBOOT" "$BOOTFS"
fi

tar -C "$ROOTFS" --numeric-owner -xf "$TAR"
for i in /dev /proc /sys; do mount --bind "$i" "$ROOTFS$i"; done

# loop device so lilo could work...
echo "$LOOPROOT / $ROOTFSTYPE relatime 1 1" >> "$ROOTFS/etc/fstab"

# target device at once
if [ -n "$BOOTPART" ]; then
	echo "$BOOTDEV /boot $BOOTFSTYPE defaults 1 2" >> "$ROOTFS/etc/fstab"
fi

echo "MODULES_PRELOAD=$INITRD_MODULES $ROOTFSTYPE" >> "$ROOTFS/etc/initrd.mk"

KERNEL="$(readlink $ROOTFS/boot/vmlinuz | sed 's,vmlinuz-,,')"
chroot "$ROOTFS" make-initrd -k "$KERNEL"

# ...target device too
sed -i "s,$LOOPROOT,$ROOTDEV," "$ROOTFS/etc/fstab"

if [ -x /sbin/lilo ]; then
	# configure and install bootloader
	REGEXP='^Disk .*: ([0-9]+) cylinders, ([0-9]+) heads, ([0-9]+) sectors/track*$'
	set -- $(sfdisk -l "$LOOPDEV" | grep -E "$REGEXP" | sed -r "s@$REGEXP@\1 \2 \3@")

	LILO_COMMON="lba32
delay=1
vga=0
image=/boot/vmlinuz
  initrd=/boot/initrd.img
  append=\"root=$ROOTDEV rootdelay=3 quiet\"
  label=linux"

	cat > "$ROOTFS"/etc/lilo-loop.conf <<-EOF
	boot=$LOOPDEV
	disk=$LOOPDEV
	  bios=0x80
	  cylinders=$1
	  heads=$2
	  sectors=$3
	  partition=$LOOPROOT
	  start=63
	$LILO_COMMON
	EOF

	chroot "$ROOTFS" lilo -C /etc/lilo-loop.conf

	cat > "$ROOTFS"/etc/lilo.conf <<-EOF
	boot=$BLOCKDEV
	$LILO_COMMON
	EOF
fi

if [ -n "$SUDO_USER" ]; then
	chown "$SUDO_USER" "$IMG" "$ROOTFS" "$WORKDIR"
fi