[slx-dmsetup] Split dmsetup-slx-device into smaller services

12 files changed, 246 insertions, 205 deletions

diff --git a/modules.d/dnbd3-rootfs/hooks/s3-dnbd3root.sh b/modules.d/dnbd3-rootfs/hooks/s3-connect-image.sh
index e78a007a..835a5613 100755
--- a/modules.d/dnbd3-rootfs/hooks/s3-dnbd3root.sh
+++ b/modules.d/dnbd3-rootfs/hooks/s3-connect-image.sh
@@ -207,9 +207,8 @@ if ! [ -b "$read_only_partition" ]; then
 fi
 
 echo "Using read-only partition: $read_only_partition"
+echo "$read_only_partition" > "/.read_only_device"
 
-# region add rw layer to dnbd3 image
-# don't be fooled to think we are done, the next part is crucial
-dmsetup-slx-device "$read_only_partition"
 settle
-# endregion
+
+exit 0
diff --git a/modules.d/dnbd3-rootfs/module-setup.sh b/modules.d/dnbd3-rootfs/module-setup.sh
index b8cc10af..67907d10 100755
--- a/modules.d/dnbd3-rootfs/module-setup.sh
+++ b/modules.d/dnbd3-rootfs/module-setup.sh
@@ -149,7 +149,7 @@ install() {
     inst_hook cmdline 90 "$moddir/hooks/set-dracut-environment-variables.sh"
     # make the final blockdevice for the root system (dnbd3 -> xmount ->
     # device-mapper)
-    slx_service "s3-dnbd3root" "Setup dnbd3-based block device of rootfs" \
+    slx_service "s3-connect-image" "Setup dnbd3-based block device of rootfs" \
         --after "s3-fetch-config.service" \
         --after "dracut-pre-mount.service" \
         --wbefore "dracut-mount.service" \
diff --git a/modules.d/slx-dmsetup/bin/dmsetup_create_noudevsync b/modules.d/slx-dmsetup/bin/dmsetup_create_noudevsync
new file mode 100755
index 00000000..ebcf5ed6
--- /dev/null
+++ b/modules.d/slx-dmsetup/bin/dmsetup_create_noudevsync
@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Helper to call 'dmsetup setup' without syncing with udev
+# and then actively create the devices with the mknodes command.
+# Either pass the table contents as $2, or pipe them into the function
+# dmsetup_create_noudevsync <name> [table]
+(
+	set -eo pipefail
+	if [ -n "$2" ]; then
+		printf "%s\n" "$2" | dmsetup create "$1" --noudevsync
+	else
+		dmsetup create "$1" --noudevsync
+	fi
+	dmsetup mknodes --noudevsync "$1"
+	echo "dm: Created $1"
+)
+ret=$?
+
+[ -b "/dev/mapper/$1" ] || ret=99
+if [ $ret -ne 0 ]; then
+	echo "dm: Error creating $1, removing..."
+	dmsetup remove --noudevsync "$1"
+fi
+
+exit $ret
diff --git a/modules.d/slx-dmsetup/hooks/dmsetup-slx-device b/modules.d/slx-dmsetup/hooks/s3-cow-setup.sh
index 05a1b823..75f0c0c4 100755
--- a/modules.d/slx-dmsetup/hooks/dmsetup-slx-device
+++ b/modules.d/slx-dmsetup/hooks/s3-cow-setup.sh
@@ -28,15 +28,21 @@ exec {BASH_XTRACEFD}> /run/openslx/dmsetup.log
 set -x
 
 # read-only device to prepare for CoW
-[ -n "$1" ] || drop_shell "Read-only device was not given!"
-[ -b "$1" ] || drop_shell "Given device '$1' does not exist or is not block device"
+[ -s "/.read_only_device" ] && read_only_device="$( cat "/.read_only_device" )"
+[ -n "$read_only_device" ] || read_only_device="$1"
+[ -n "$read_only_device" ] || drop_shell 'Read only device neither given via /.read_only_device nor $1'
 
-declare -g read_only_device="$1"
-declare -g read_only_device_sz="$( blockdev --getsz "$1" )"
-# Use _sz suffix for sizes expressed in number of 512b sectors,
-# _size for random other crap
+[ -b "$read_only_device" ] || drop_shell "Given device '$1' does not exist or is not block device"
 
-declare -rg ntfs_list="/run/openslx/.thin-ntfs-candidates"
+declare -g read_only_device_sz="$( blockdev --getsz "$read_only_device" )"
+# !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+# !! Use _sz suffix for sizes expressed in number of 512b sectors, !!
+# !! _size for random other crap                                   !!
+# !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+
+if ! (( read_only_device_sz > 0 )); then
+	drop_shell "Could not determine size of read only device '$read_only_device'"
+fi
 
 # handle_unit <value> <unit>
 # Supply percentage, or size in [kmgt]bytes,
@@ -153,30 +159,6 @@ parse_config_int() {
 	done <<< "$1"
 }
 
-# Helper to call 'dmsetup setup' without syncing with udev
-# and then actively create the devices with the mknodes command.
-# Either pass the table contents as $2, or pipe them into the function
-# dmsetup_create_noudevsync <name> [table]
-dmsetup_create_noudevsync() {
-	(
-		set -eo pipefail
-		if [ -n "$2" ]; then
-			printf "%s\n" "$2" | dmsetup create "$1" --noudevsync
-		else
-			dmsetup create "$1" --noudevsync
-		fi
-		dmsetup mknodes --noudevsync "$1"
-		echo "dm: Created $1"
-	)
-	local ret=$?
-	[ -b "/dev/mapper/$1" ] || ret=99
-	if [ $ret -ne 0 ]; then
-		echo "dm: Error creating $1, removing..."
-		dmsetup remove --noudevsync "$1"
-	fi
-	return $ret
-}
-
 # encrypt_device <dev_path> <encrypted_name> [<start> <size>]
 encrypt_device() {
 	# TODO: Send key back to us, demand ransom
@@ -383,28 +365,6 @@ create_pool() {
 	# calculate number of sectors needed and check boundaries:
 	# XXX Formula from thin-pool.txt calculates size in *bytes*, we want 512b blocks
 	metadata_dev_sz="$(( 48 * scratch_device_sz / data_block_sz / 512 ))"
-	# If we want NTFS as a backup plan to extend the pool, check if the current size
-	# is less than 100GB, and only then consider this feature.
-	# Maybe make that thresold configurable one day, but for the desktop client
-	# use case this is sensible for now.
-	if [ "$SLX_NTFSFREE" = "backup" ] && (( scratch_device_sz < 209715200 )) \
-			&& [ -z "$metadata_persistent" ]; then
-		echo "pool: Considering NTFS partitions as backup since pool is small"
-		find_ntfs_partitions
-		if [ -s "$ntfs_list" ]; then
-			# Look what size we end up if we want at least 50GB
-			local sum="$( awk -v sum=0 \
-				'{sum+=$1; if (sum >= 104857600) exit}END{printf "%.0f", sum}' \
-				"$ntfs_list" )"
-			if (( sum > 0 )); then
-				(( sum > 209715200 )) && sum=209715200 # Max 100GB
-				# Account for this potential growth in the metadata device size for future expansion
-				metadata_dev_sz="$(( metadata_dev_sz + 48 * sum / data_block_sz / 512 ))"
-				echo "$sum" > "/run/openslx/.thin-ntfs-growsize"
-				root_ntfs_extra="$sum"
-			fi
-		fi
-	fi
 	# Min 2MB -> 4096 sectors, max 16GB -> 33554432 sectors
 	[ "$metadata_dev_sz" -lt 4096 ] && metadata_dev_sz="4096"
 	# TODO handle the exotic case of a too large metadata device to fit within RAM.
@@ -446,7 +406,7 @@ create_pool() {
 	fi
 
 	local pool_data_dev
-	if (( root_ntfs_extra == 0 )) && (( scratch_device_offset == 0 )); then
+	if (( scratch_device_offset == 0 )); then
 		# No offset, no potential expansion, don't create another linear target
 		pool_data_dev="$scratch_device"
 	else
@@ -502,140 +462,32 @@ create_volume() {
 	return 0
 }
 
-# Find NTFS partitions with decently sized ranges of
-# free space. We can use these as our writable layer
-# for our thin-pool, if configured.
-# If suitable, this will create the file $ntfs_list with
-# one line per suitable partition, format
-# total_size_blocks devpath
-# Results are sorted by size, descending order
-find_ntfs_partitions() {
-	[ -z "$SLX_NTFSFREE" ] && return
-	[ "$SLX_NTFSFREE" = "never" ] && return
-	[ -e "$ntfs_list" ] && return
-	echo "ntfs: Scanning for suitable NTFS partitions to use as writable device"
-	if ! command -v ntfsfree &> /dev/null; then
-		echo "ntfs: ntfsfree not found, cannot use NTFS partitions as RW layer"
-		return
-	fi
-	local part sum ro dev
-	ntfs_extra_space_sz=0
-	for part in /dev/disk/by-partuuid/*; do
-		# Skip empty/ro devices
-		dev="$( readlink -f "$part" )"
-		dev="${dev##*/}"
-		ro="$( cat "/sys/class/block/${dev}/ro" )"
-		[ "$ro" = 1 ] && continue
-		# Only count ranges >= 256MB, sum will be in number of 512b blocks
-		sum="$( ntfsfree --block-size 512 --min-size "$(( 256 * 1024 * 1024 ))" "$part" 2> /dev/null \
-			| awk -v sum=0 '{if ($1 == "Range") sum += $4}END{printf "%.0f", sum}' )"
-		# Only consider volume if sum of these ranges > 1GB (this is BLOCKS, not bytes)
-		(( sum > 2 * 1024 * 1024 )) || continue
-		echo "$sum $part" # only thing in loop going to stdout
-		(( ntfs_extra_space_sz += sum ))
-	done | sort -nr > "$ntfs_list"
-	echo "ntfs: Found $( wc -l < "$ntfs_list" ) suitable partitions"
-}
-ntfs_extra_space_sz=0
-
 ###
 ##	MAIN
 ###
 
 . /etc/openslx
-
 . slx-tools
-# "Preload" functions by executing them NOT in a subshell
-dev_find_partitions &> /dev/null
-dev_swap_version &> /dev/null
 
 # This is the main variable driving this script
+declare -g writable_device="$( cat "/.writable_device" )"
 declare -g id44_crypted=
-declare -g writable_device=
-if [ -z "$SLX_WRITABLE_DEVICE_IDENTIFIER" ]; then
-	SLX_WRITABLE_DEVICE_IDENTIFIER="44 87f86132-ff94-4987-b250-444444444444"
-	echo "SLX_WRITABLE_DEVICE_IDENTIFIER='${SLX_WRITABLE_DEVICE_IDENTIFIER}'" >> /etc/openslx
-fi
 
-if [ -n "$SLX_WRITABLE_DEVICE_IDENTIFIER" ]; then
-	unset writable_devices
-	declare -a writable_devices
-	read -r -a list <<<"$SLX_WRITABLE_DEVICE_IDENTIFIER"
-	echo "Scanning for partitions with type/label ${list[*]}..."
-	while read -r -a list; do
-		writable_devices+=( "${list[@]}" )
-	done < <( dev_find_partitions "${list[@]}" )
-	echo "Found ${#writable_devices[@]} matching partitions"
-	if [[ "${#writable_devices[@]}" -eq 0 && "$SLX_NTFSFREE" != "never" ]] || [ "$SLX_NTFSFREE" = "always" ]; then
-		find_ntfs_partitions
-	fi
-	if [ -s "$ntfs_list" ] || [[ "${#writable_devices[@]}" -gt 1 ]]; then
-		# More than one device, and/or NTFS space, need linear
-		echo "Have more than one writable device, creating linear target"
-		tbl="/run/openslx/dmsetup-linear-id44"
-		pos=0
-		grow_max_sz=9999999999
-		for dev in "${writable_devices[@]}"; do
-			max="$(( grow_max_sz - pos ))"
-			(( max <= 0 )) && break
-			sz="$( blockdev --getsz "$dev" )"
-			(( sz > 0 )) || continue
-			(( sz > max )) && sz="$max"
-			echo "$pos $sz linear $dev 0"
-			(( pos += sz ))
-		done > "$tbl"
-		if [ -s "$ntfs_list" ]; then
-			sum=
-			while read -r sum dev _ || [ -n "$sum" ]; do # each dev
-				echo "Appending NTFS partition $dev..."
-				word=
-				while read -r word range_start_b _ range_sz _ || [ -n "$word" ]; do # each slice of dev
-					[ "$word" = "Range" ] || continue
-					(( range_sz > 0 )) || continue
-					slice_sz="$(( grow_max_sz - pos ))"
-					(( slice_sz <= 0 )) && break
-					(( slice_sz > range_sz )) && slice_sz="$range_sz"
-					# Append line
-					if echo "$pos $slice_sz linear $dev $range_start_b" >> "$tbl"; then
-						# Update counter
-						(( pos += slice_sz ))
-					else
-						echo "Could not write new table row into $tbl"
-					fi
-				done < <( ntfsfree --block-size 512 --min-size "$(( 256 * 1024 * 1024 ))" "$dev" )
-			done < "$ntfs_list"
-			# Don't try to add NTFS space again later
-			SLX_NTFSFREE="never"
-			sed -i "s/^SLX_NTFSFREE.*$/# & # disabled in stage3\nSLX_NTFSFREE='never'/" "/etc/openslx"
-			rm -f -- "$ntfs_list"
-		fi
-		# See if we need a linear target at all
-		if ! [ -s "$tbl" ]; then
-			echo "Empty tmp/id44 table, fallback to RAM"
-		elif [ "$( wc -l < "$tbl" )" -eq 1 ] && [[ "${#writable_devices[@]}" -ge 1 ]]; then
-			# Only one line, have writable device -> use directly
-			echo "Table somehow ended up with one entry, discarding"
-			writable_device="${writable_devices[0]}"
-		else
-			# set up linera device
-			echo "Setting up linear id44 device with $( wc -l < "$tbl" ) slices"
-			if ! dmsetup_create_noudevsync "id44-group" < "$tbl"; then
-				echo "$0: Error creating group of writable devices. Fallback to RAM :-("
-			else
-				writable_device="/dev/mapper/id44-group"
-			fi
-		fi
-	else
-		# Single device
-		echo "Have a single writable device, using it directly"
-		writable_device="${writable_devices[0]}"
-	fi
-fi
 if [ -z "$writable_device" ]; then
-	echo "Could not find writable device with id(s) '$SLX_WRITABLE_DEVICE_IDENTIFIER'."
+	echo "No writable device"
 	ramdisk_fallback
-elif is_on "$SLX_ID44_CRYPT"; then
-	# Config option crypts the entire ID44 device(s), before any slices are taken from it.
+	exit 0
+fi
+
+if ! [ -b "$writable_device" ]; then
+	drop_shell "Writable device '$writable_device' not a block device"
+fi
+
+# "Preload" functions by executing them NOT in a subshell
+dev_find_partitions &> /dev/null
+
+# Handle global encryption first
+if is_on "$SLX_ID44_CRYPT"; then
 	if encrypt_device "$writable_device" "id44-crypt"; then
 		writable_device="/dev/mapper/id44-crypt"
 		# Remember the whole device is already encrypted, and ignore the crypt flag for the partition table later
@@ -645,6 +497,9 @@ fi
 
 # NOTE: from here on out, every value related to size is in 512 bytes sectors!
 declare -rg writable_device_sz="$( blockdev --getsz "$writable_device" )"
+if ! (( writable_device > 0 )); then
+	drop_shell "Could not determine size of writable device '$writable_device'"
+fi
 
 # If SLX_WRITABLE_DEVICE_PARTITION_TABLE is not set, just do
 # regular thin-snapshot for the CoW layer, else parse it.
@@ -652,7 +507,7 @@ if [ -z "$SLX_WRITABLE_DEVICE_PARTITION_TABLE" ]; then
 	SLX_WRITABLE_DEVICE_PARTITION_TABLE="thin-snapshot root 100% 0"
 fi
 
-# extra swap?
+# extra swap if no existing?
 if grep -qFw 'slx.swap' "/proc/cmdline"; then
 	# Only if our basic writable_device is large enough, or we have ntfs backup
 	echo "Additional swap on ID44 requested if existing is too small"
@@ -662,22 +517,13 @@ if grep -qFw 'slx.swap' "/proc/cmdline"; then
 		do_swap_sz="$(( ( writable_device_sz - 70312500 ) / 2 ))"
 		# cap to 6GB
 		(( do_swap_sz > 11718750 )) && do_swap_sz=11718750
-	elif [ "$SLX_NTFSFREE" = "backup" ] \
-			&& (( ntfs_extra_space_sz > 70312500 )) && (( writable_device_sz > 11718750 )); then
-		# more than 40GB NTFS backup space, more than 6GB ID44, make 4GB swap
-		do_swap_sz=7812500
 	fi
 	# Check how many we have and if they're regular, unencrypted ones.
 	# If it's plenty, don't cut out swap from our backing device
-	swap_sz=0
 	if (( do_swap_sz == 0 )); then
 		echo "Not enough ID44 space for swap..."
 	else
-		for part in $( dev_find_partitions "82" "0657fd6d-a4ab-43c4-84e5-0933c84b4f4f" ); do
-			dev_swap_version "$part" &> /dev/null || continue
-			this_sz="$( blockdev --getsz "$part" )"
-			(( this_sz > 0 )) && (( swap_sz += this_sz ))
-		done
+		swap_sz="$( awk '$1 == "SwapTotal:" {print $2 * 2}' /proc/meminfo )"
 		echo "Have existing swap of $(( swap_sz / 2 / 1024 ))MiB"
 		(( do_swap_sz -= swap_sz ))
 		# Go ahead with swap? Only if we miss a reasonable amount... ( > 100MiB)
@@ -801,7 +647,6 @@ done
 ##	THIN-PROVISIONING
 ###
 declare -rg pool_dev="/dev/mapper/pool"
-declare -gi root_ntfs_extra=0 # Extra blocks to provision to root fs for later expansion
 # Now decide what to do for the writable layer
 
 if [ -n "$thin_snapshot" ] || [ -n "${thin_volume[*]}" ]; then
@@ -863,12 +708,6 @@ if [ -n "$thin_snapshot" ] || [ -n "${thin_volume[*]}" ]; then
 			reserved_sz="$(( read_only_device_sz / 2 ))"
 			(( reserved_sz > max_reserved_sz )) && reserved_sz="$max_reserved_sz"
 			thin_snapshot_sz="$(( scratch_device_sz + read_only_device_sz - reserved_sz ))"
-			# For later on-demand growing, overprovision by free space we found on
-			# clean NTFS volumes. This requires a user-space helper to listen for
-			# dm events in stage4, which should in turn add that free space to the pool-data
-			if (( root_ntfs_extra > 0 )); then
-				thin_snapshot_sz="$(( thin_snapshot_sz + root_ntfs_extra ))"
-			fi
 			if ! create_volume "$name" 1 "$thin_snapshot_sz" "$read_only_device"; then
 				echo "Error: Failed to create external snapshot for '$read_only_device'." >&2
 				ramdisk_fallback # does not return
diff --git a/modules.d/slx-dmsetup/hooks/s3-mount-swap.sh b/modules.d/slx-dmsetup/hooks/s3-mount-swap.sh
new file mode 100755
index 00000000..0384bcf4
--- /dev/null
+++ b/modules.d/slx-dmsetup/hooks/s3-mount-swap.sh
@@ -0,0 +1,10 @@
+#!/bin/ash
+
+. slx-tools
+
+for part in $( dev_find_partitions "82" "0657fd6d-a4ab-43c4-84e5-0933c84b4f4f" ); do
+	dev_swap_version "$part" &> /dev/null || continue
+	swapon "$part"
+done
+
+exit 0
diff --git a/modules.d/slx-dmsetup/hooks/s3-prepare-rw-layer.sh b/modules.d/slx-dmsetup/hooks/s3-prepare-rw-layer.sh
new file mode 100755
index 00000000..69fc75d2
--- /dev/null
+++ b/modules.d/slx-dmsetup/hooks/s3-prepare-rw-layer.sh
@@ -0,0 +1,80 @@
+#!/bin/bash
+
+if ! [ -e "/.writable_devices" ]; then
+	echo "/.writable_devices not found"
+	exit 1
+fi
+mapfile -t writable_devices < /.writable_devices
+
+declare -rg ntfs_list="/run/openslx/.thin-ntfs-candidates"
+
+. slx-tools
+
+if [ -s "$ntfs_list" ] || [[ "${#writable_devices[@]}" -gt 1 ]]; then
+	# More than one device, and/or NTFS space, need linear
+	echo "Have more than one writable device, creating linear target"
+	tbl="/run/openslx/dmsetup-linear-id44"
+	pos=0
+	grow_max_sz=9999999999
+	for dev in "${writable_devices[@]}"; do
+		max="$(( grow_max_sz - pos ))"
+		(( max <= 0 )) && break
+		sz="$( blockdev --getsz "$dev" )"
+		(( sz > 0 )) || continue
+		(( sz > max )) && sz="$max"
+		echo "$pos $sz linear $dev 0"
+		(( pos += sz ))
+	done > "$tbl"
+	if [ -s "$ntfs_list" ]; then
+		sum=
+		while read -r sum dev _ || [ -n "$sum" ]; do # each dev
+			echo "Appending NTFS partition $dev..."
+			word=
+			while read -r word range_start_b _ range_sz _ || [ -n "$word" ]; do # each slice of dev
+				[ "$word" = "Range" ] || continue
+				(( range_sz > 0 )) || continue
+				slice_sz="$(( grow_max_sz - pos ))"
+				(( slice_sz <= 0 )) && break
+				(( slice_sz > range_sz )) && slice_sz="$range_sz"
+				# Append line
+				if echo "$pos $slice_sz linear $dev $range_start_b" >> "$tbl"; then
+					# Update counter
+					(( pos += slice_sz ))
+				else
+					echo "Could not write new table row into $tbl"
+				fi
+			done < <( ntfsfree --block-size 512 --min-size "$(( 256 * 1024 * 1024 ))" "$dev" )
+		done < "$ntfs_list"
+		# Don't try to add NTFS space again later
+		sed -i "s/^SLX_NTFSFREE.*$/# & # disabled in stage3\nSLX_NTFSFREE='never'/" "/etc/openslx"
+		rm -f -- "$ntfs_list"
+	fi
+	# See if we need a linear target at all
+	if ! [ -s "$tbl" ]; then
+		echo "Empty tmp/id44 table, fallback to RAM"
+	elif [ "$( wc -l < "$tbl" )" -eq 1 ] && [[ "${#writable_devices[@]}" -ge 1 ]]; then
+		# Only one line, have writable device -> use directly
+		echo "Table somehow ended up with one entry, discarding"
+		writable_device="${writable_devices[0]}"
+	else
+		# set up linear device
+		echo "Setting up linear id44 device with $( wc -l < "$tbl" ) slices"
+		if ! dmsetup_create_noudevsync "id44-group" < "$tbl"; then
+			echo "Error creating group of writable devices. Fallback to RAM :-("
+		else
+			writable_device="/dev/mapper/id44-group"
+		fi
+	fi
+else
+	# Single device
+	echo "Have a single writable device, using it directly"
+	writable_device="${writable_devices[0]}"
+fi
+
+if [ -z "$writable_device" ]; then
+	echo "Could not find any suitable writable devices."
+fi
+
+echo "$writable_device" > "/.writable_device"
+
+exit 0
diff --git a/modules.d/slx-dmsetup/hooks/s3-scan-id44.sh b/modules.d/slx-dmsetup/hooks/s3-scan-id44.sh
new file mode 100755
index 00000000..60ba133d
--- /dev/null
+++ b/modules.d/slx-dmsetup/hooks/s3-scan-id44.sh
@@ -0,0 +1,23 @@
+#!/bin/bash
+
+. /etc/openslx
+. slx-tools
+
+if [ -z "$SLX_WRITABLE_DEVICE_IDENTIFIER" ]; then
+	SLX_WRITABLE_DEVICE_IDENTIFIER="44 87f86132-ff94-4987-b250-444444444444"
+	echo "SLX_WRITABLE_DEVICE_IDENTIFIER='${SLX_WRITABLE_DEVICE_IDENTIFIER}'" >> /etc/openslx
+fi
+
+declare -a writable_devices
+read -r -a list <<<"$SLX_WRITABLE_DEVICE_IDENTIFIER"
+echo "Scanning for partitions with type/label ${list[*]}..."
+for dev in $( dev_find_partitions "${list[@]}" ); do
+	writable_devices+=( "$dev" )
+done
+echo "Found ${#writable_devices[@]} matching partitions"
+
+for dev in "${writable_devices[@]}"; do
+	echo "$dev"
+done > "/.writable_devices"
+
+exit 0
diff --git a/modules.d/slx-dmsetup/module-setup.sh b/modules.d/slx-dmsetup/module-setup.sh
index 99c1adf2..e513ca6f 100755
--- a/modules.d/slx-dmsetup/module-setup.sh
+++ b/modules.d/slx-dmsetup/module-setup.sh
@@ -6,9 +6,10 @@ depends() {
 	echo "haveged slx-tools"
 }
 install() {
-	inst "$moddir/hooks/dmsetup-slx-device" "/usr/local/bin/dmsetup-slx-device"
+	inst "$moddir/bin/dmsetup_create_noudevsync" "/usr/local/bin/dmsetup_create_noudevsync"
 
 	# Grows the rootfs to match the underlying blockdev
+	# No using slx install helper because of additional condition
 	_name="s3-grow-rootfs"
 	inst "$moddir/hooks/${_name}.sh" \
 			"/usr/local/bin/${_name}.sh"
@@ -19,12 +20,24 @@ install() {
 	ln_r "${systemdsystemunitdir}/${_name}.service" \
 			"${systemdsystemunitdir}/initrd.target.wants/${_name}.service"
 
+	slx_service "s3-cow-setup" "Set up the CoW layer for rootfs" \
+		--wafter   "s3-connect-image.service" \
+		--before   "initrd-root-device.target" \
+		--after    "s3-fetch-config.service"
+
+	slx_service "s3-mount-swap" "Mount existing swap partitions" \
+		--before   "s3-cow-setup"
+
+	slx_service "s3-prepare-rw-layer" "Prepare suitable partitions for use as write layer" \
+		--before   "s3-cow-setup"
+
+	slx_service "s3-scan-id44" "Scan for partitions marked as scratch space (ID44)" \
+		--before   "s3-prepare-rw-layer.service" \
+		--after    "s3-fetch-config.service"
+
 	inst_multiple blockdev xxd \
 		mkfs.ext4 resize2fs \
 		mkfs.xfs xfs_repair xfs_growfs
-
-	# TODO properly find binary in PATH + /opt/openslx/{s,}bin etc
-	inst /opt/openslx/sbin/ntfsfree /usr/local/bin/ntfsfree
 }
 installkernel() {
 	# install those modules in case the used kernel does not have them builtin
diff --git a/modules.d/slx-extra-script/module-setup.sh b/modules.d/slx-extra-script/module-setup.sh
index 9cc9bdbe..0c3600e2 100755
--- a/modules.d/slx-extra-script/module-setup.sh
+++ b/modules.d/slx-extra-script/module-setup.sh
@@ -9,7 +9,8 @@ depends() {
 install() {
 	slx_service "s3-extra-script" "Execute extra script from URL" \
 		--wafter "s3-fetch-config.service" \
-		--before "s3-dnbd3root.service"
+		--before "s3-connect-image.service" \
+		--before "s3-prepare-rw-layer.service"
 	mkdir --parents "${initdir}/${systemdsystemunitdir}/initrd.target.wants"
 	local i
 	for i in dmsetup mount; do
diff --git a/modules.d/slx-extra-script/services/s3-extra-post-dmsetup.service b/modules.d/slx-extra-script/services/s3-extra-post-dmsetup.service
index fd1f18e6..a7d8a6fe 100644
--- a/modules.d/slx-extra-script/services/s3-extra-post-dmsetup.service
+++ b/modules.d/slx-extra-script/services/s3-extra-post-dmsetup.service
@@ -1,7 +1,7 @@
 [Unit]
 Description=Run extra script after dmsetup
 ConditionFileIsExecutable=/etc/extra-init
-After=s3-dnbd3root.service
+After=s3-cow-setup.service
 Before=s3-write-fstab.service
 Before=initrd-switch-root.target initrd-cleanup.service
 
diff --git a/modules.d/slx-ntfsfree/hooks/s3-ntfsfree.sh b/modules.d/slx-ntfsfree/hooks/s3-ntfsfree.sh
new file mode 100755
index 00000000..0c663ef3
--- /dev/null
+++ b/modules.d/slx-ntfsfree/hooks/s3-ntfsfree.sh
@@ -0,0 +1,30 @@
+#!/bin/bash
+
+. /etc/openslx
+[ "${SLX_NTFSFREE:-never}" = "never" ] && exit 0
+
+declare -rg ntfs_list="/run/openslx/.thin-ntfs-candidates"
+[ -e "$ntfs_list" ] && exit 0
+
+echo "Scanning for suitable NTFS partitions to use as writable device"
+if ! command -v ntfsfree &> /dev/null; then
+	echo "ntfsfree not found, cannot use NTFS partitions as RW layer"
+	exit 1
+fi
+
+for part in /dev/disk/by-partuuid/*; do
+	# Skip empty/ro devices
+	dev="$( readlink -f "$part" )"
+	dev="${dev##*/}"
+	ro="$( cat "/sys/class/block/${dev}/ro" )"
+	[ "$ro" = 1 ] && continue
+	# Only count ranges >= 256MB, sum will be in number of 512b blocks
+	sum="$( ntfsfree --block-size 512 --min-size "$(( 256 * 1024 * 1024 ))" "$part" 2> /dev/null \
+		| awk -v sum=0 '{if ($1 == "Range") sum += $4}END{printf "%.0f", sum}' )"
+	# Only consider volume if sum of these ranges > 1GB (this is BLOCKS, not bytes)
+	(( sum > 2 * 1024 * 1024 )) || continue
+	echo "$sum $part" # only thing in loop going to stdout
+done | sort -nr > "$ntfs_list"
+echo "Found $( wc -l < "$ntfs_list" ) suitable partitions"
+
+exit 0
diff --git a/modules.d/slx-ntfsfree/module-setup.sh b/modules.d/slx-ntfsfree/module-setup.sh
new file mode 100755
index 00000000..dabe2dda
--- /dev/null
+++ b/modules.d/slx-ntfsfree/module-setup.sh
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+check() {
+	return 255
+}
+depends() {
+	echo "slx-tools"
+}
+install() {
+	slx_service "s3-ntfsfree" "Scan for free space on NTFS partitions" \
+		--wafter   "s3-fetch-config.service"
+		--before   "s3-prepare-rw-layer"
+	# TODO properly find binary in PATH + /opt/openslx/{s,}bin etc
+	inst /opt/openslx/sbin/ntfsfree /usr/local/bin/ntfsfree
+}
+installkernel() {
+	# install those modules in case the used kernel does not have them builtin
+	instmods \
+		dm-thin-pool dm-snapshot dm-zero dm-crypt \
+		crc32c xts aes drbg ansi_cprng \
+		xfs ext4
+}