diff --git a/bin/tar2fs b/bin/tar2fs
new file mode 100755
index 00000000..8c77778b
--- /dev/null
+++ b/bin/tar2fs
@@ -0,0 +1,236 @@
+#!/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
diff --git a/bin/tar2vm b/bin/tar2vm
deleted file mode 100755
index 4aad1675..00000000
--- a/bin/tar2vm
+++ /dev/null
@@ -1,134 +0,0 @@
-#!/bin/bash -e
-# usage:
-# tar2vm chroot.tar image.raw [size_in_bytes]
-
-. shell-error
-
-if [ $# -lt 2 ]; then
-	fatal "error: tar2vm needs at least two arguments"
-fi
-
-# this needs env_keep sudo setup to actually work
-if [ -n "$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"
-
-# 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 "$IMG")" ] || fatal "target directory doesn't exist"
-
-# image size in bytes (256M is a fallback)
-TARSIZE="$(stat -Lc %s "$TAR")"
-DEFSIZE="$((2 * $TARSIZE))"
-DISKSIZE="${3:-${DEFSIZE:-268435456}}"
-# ...and in megabytes
-DISKSIZEM="$(($DISKSIZE / 1048576))"
-
-# tested to work: ext[234], jfs
-# NB: xfs doesn't have a spare sector for the bootloader
-ROOTFSTYPE="${4:-ext4}"
-
-# single root partition hardwired so far,
-# add another image for swap if needed
-ROOTDEV="/dev/sda1"
-
-# last preparations...
-for i in losetup sfdisk parted kpartx mkfs."$ROOTFSTYPE"; do
-	if ! type -t "$i" >&/dev/null; then
-		fatal "$i required but not found"
-	fi
-done
-
-LOOPDEV="$(losetup --find)"
-ROOTFS="$WORKDIR/chroot"
-
-exit_handler()
-{
-	rc=$?
-	if [ -n "$ROOTFS" ]; then
-		umount "$ROOTFS"{/dev,/proc,/sys,}
-		if [ -n "$LOOPDEV" ]; then
-			kpartx -d "$LOOPDEV"
-			losetup --detach "$LOOPDEV"
-		fi
-		rm -r -- "$ROOTFS"
-		rmdir -- "$WORKDIR"
-	fi
-	exit $rc
-}
-
-trap exit_handler EXIT
-
-# prepare disk image and a filesystem inside it
-rm -f -- "$IMG"
-dd if=/dev/zero of="$IMG" conv=notrunc \
-	bs=1 count=1 seek="$(($DISKSIZE - 1))"
-losetup "$LOOPDEV" "$IMG"
-
-parted --script "$LOOPDEV" mklabel msdos
-parted --script "$LOOPDEV" mkpart primary ext2 1 "$DISKSIZEM"
-
-kpartx -a "$LOOPDEV"
-LOOPDEV1="/dev/mapper/$(basename "$LOOPDEV")p1"
-
-mkfs."$ROOTFSTYPE" "$LOOPDEV1"
-
-# mount and populate it
-mkdir -pm755 "$ROOTFS"
-mount "$LOOPDEV1" "$ROOTFS"
-tar -C "$ROOTFS" --numeric-owner -xf "$TAR"
-for i in /dev /proc /sys; do mount --bind "$i" "$ROOTFS$i"; done
-
-# NB: different storage modules might be needed for non-kvm
-echo "$LOOPDEV1 / $ROOTFSTYPE defaults 1 1" >> "$ROOTFS/etc/fstab"
-echo "MODULES_PRELOAD=sd_mod ata_piix $ROOTFSTYPE" >> "$ROOTFS/etc/initrd.mk"
-
-KERNEL="$(readlink $ROOTFS/boot/vmlinuz | sed 's,vmlinuz-,,')"
-chroot "$ROOTFS" make-initrd -k "$KERNEL"
-
-sed -i "s,$LOOPDEV1,$ROOTDEV," "$ROOTFS/etc/fstab"
-
-# 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=$ROOTDEV rootdelay=3\"
-  label=linux"
-
-cat > "$ROOTFS"/etc/lilo-loop.conf << EOF
-boot=$LOOPDEV
-disk=$LOOPDEV
-  bios=0x80
-  cylinders=$1
-  heads=$2
-  sectors=$3
-  partition=$LOOPDEV1
-  start=63
-$LILO_COMMON
-EOF
-
-chroot "$ROOTFS" lilo -C /etc/lilo-loop.conf
-
-cat > "$ROOTFS"/etc/lilo.conf << EOF
-boot=${ROOTDEV%[0-9]*}
-$LILO_COMMON
-EOF
-
-if [ -n "$SUDO_USER" ]; then
-	chown "$SUDO_USER" "$IMG" "$ROOTFS" "$WORKDIR"
-fi
diff --git a/doc/params.txt b/doc/params.txt
index d2c94be1..0d580220 100644
--- a/doc/params.txt
+++ b/doc/params.txt
@@ -109,7 +109,7 @@
 * VM_SIZE
 ** задаёт размер несжатого образа виртуальной машины в байтах
 ** значение: пусто (по умолчанию двойной размер чрута) или целое
-** см. ../features.in/build-vm/lib/90-build-vm.mk, ../bin/tar2vm
+** см. ../features.in/build-vm/lib/90-build-vm.mk, ../bin/tar2fs
 
 [float]
 === пример ===
diff --git a/doc/vm.txt b/doc/vm.txt
index d7b727a3..c486ebb8 100644
--- a/doc/vm.txt
+++ b/doc/vm.txt
@@ -2,14 +2,14 @@
 
 *ВНИМАНИЕ:* заключительная операция создания образа жёсткого диска
 из архива с содержимым корневой файловой системы требует доступа
-к sudo и разрешения на выполнение скрипта bin/tar2vm в корневом
+к sudo и разрешения на выполнение скрипта bin/tar2fs в корневом
 каталоге метапрофиля при установке mkimage-profiles из пакета
 (это в планах исправить, но подход к libguestfs пока успехом
 не увенчался).
 
 Соответствующий фрагмент конфигурации sudo(8) может выглядеть как:
 
-  mike ALL=NOPASSWD: /usr/share/mkimage-profiles/bin/tar2vm
+  mike ALL=NOPASSWD: /usr/share/mkimage-profiles/bin/tar2fs
 
 При работе с локальной копией mkimage-profiles.git следует иметь
 в виду, что предоставлять недоверенному пользователю право выполнять
@@ -25,3 +25,10 @@
 Пример сборки и запуска VM:
 
   $ make ROOTPW=reallysecret1 vm/bare.img && kvm -hda ~/out/bare.img
+
+Если при сборке образа файловой системы произойдёт сбой, может оказаться
+нужным вручную освободить используемые loop-устройства, например, так:
+
+  # losetup -a
+  # kpartx -d /dev/loop0
+  # losetup -d /dev/loop0
diff --git a/features.in/build-vm/generate.mk b/features.in/build-vm/generate.mk
index 399baf74..b2ef598f 100644
--- a/features.in/build-vm/generate.mk
+++ b/features.in/build-vm/generate.mk
@@ -1,4 +1,4 @@
-# copy tar2vm helper into generated profile to enable standalone builds
+# copy tar2fs helper into generated profile to enable standalone builds
 
 all:
-	@install -pD $(MKIMAGE_PROFILES)/bin/tar2vm $(BUILDDIR)/bin/tar2vm
+	@install -pD $(MKIMAGE_PROFILES)/bin/tar2fs $(BUILDDIR)/bin/tar2fs
diff --git a/features.in/build-vm/lib/90-build-vm.mk b/features.in/build-vm/lib/90-build-vm.mk
index 20c6296a..2bb27d77 100644
--- a/features.in/build-vm/lib/90-build-vm.mk
+++ b/features.in/build-vm/lib/90-build-vm.mk
@@ -10,6 +10,8 @@ IMAGE_PACKAGES = $(DOT_BASE) \
 # intermediate chroot archive
 VM_TARBALL := $(IMAGE_OUTDIR)/$(IMAGE_NAME).tar
 VM_RAWDISK := $(IMAGE_OUTDIR)/$(IMAGE_NAME).raw
+VM_FSTYPE ?= ext4
+VM_SIZE ?= 0
 
 check-sudo:
 	@if ! type -t sudo >&/dev/null; then \
@@ -18,9 +20,9 @@ check-sudo:
 	fi
 
 prepare-image: check-sudo
-	@if ! sudo $(TOPDIR)/bin/tar2vm \
-		"$(VM_TARBALL)" "$(VM_RAWDISK)" $$VM_SIZE; then \
-		echo "** error: sudo tar2vm failed, see also doc/vm.txt" >&2; \
+	@if ! sudo $(TOPDIR)/bin/tar2fs \
+		"$(VM_TARBALL)" "$(VM_RAWDISK)"  $(VM_SIZE) $(VM_FSTYPE); then \
+		echo "** error: sudo tar2fs failed, see also doc/vm.txt" >&2; \
 		exit 1; \
 	fi