From 9dbfe12bc718091565a2c211d0d818f6233c4d9d Mon Sep 17 00:00:00 2001
From: Jonathan Bauer
Date: Tue, 19 Nov 2019 17:53:43 +0100
Subject: make code better

---
 .../slx-dmsetup/scripts/dmsetup-slx-device         | 64 +++++++++++++---------
 1 file changed, 38 insertions(+), 26 deletions(-)

diff --git a/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device b/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device
index d65c0dbb..71b82b9c 100755
--- a/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device
+++ b/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device
@@ -95,7 +95,7 @@ parse_config() {
 dmsetup_create_noudevsync() {
 	(
 		set -o errexit
-		dmsetup create "$1" --noudevsync --table "$2"
+		printf "%s\n" "$2" | dmsetup create "$1" --noudevsync
 		dmsetup mknodes --noudevsync "$1"
 	)
 	local ret=$?
@@ -129,12 +129,38 @@ create_snapshot() {
 	return 0
 }
 
-# Call this to fallback to a RAMdisk stored under /run/openslx
-# This will call terminate the whole script by calling finish_setup, if successful
+# This function is called if no ID44 partition could be found or anoother kind
+# of critical error occurs during the CoW layer setup. It will combine the
+# the read-only device with a DM zero device to increase its virtual size
+# by half the RAM size. A sparse file of that size will then be created and
+# placed on a dedicated tmpfs.
 ramdisk_fallback() {
 	echo "$0: Falling back to regular dm-snapshot on a RAMdisk."
-	# first we create a dedicated tmpfs to control the maximum size
-	local cow_tmpfs="/run/openslx/dnbd-cow"
+
+	# RAM size in kb, note that this is equal to half
+	# of the entire RAM in 512-bytes sectors.
+	local ram_size_in_kb="$(awk '/MemTotal/ {printf("%d\n", $2 )}' /proc/meminfo)"
+	
+	#	try to prepare the zero extension device
+	local extended_device="/dev/mapper/${read_only_device##*/}-extended"
+	(
+		set -x
+		lsmod | grep -q dm-zero || modprobe dm-zero
+		dmsetup_create_noudevsync zero "0 $ram_size_in_kb zero"
+		dmsetup_create_noudevsync "${extended_device##*/}" \
+			"0 $read_only_device_size linear $read_only_device 0
+		  $read_only_device_size $ram_size_in_kb linear /dev/mapper/zero 0"
+	)
+	if [ "$?" -eq 0 ]; then
+		read_only_device="$extended_device"
+		read_only_device_size="$(( read_only_device_size + ram_size_in_kb ))"
+	else
+		echo "$0: Failed to setup the fake larger '$read_only_device'."
+		echo "$0: Continuing with its original size."
+	fi
+
+	# prepare dedicated tmpfs mount point
+	local cow_tmpfs="/run/openslx/cow"
 	if ! mkdir -p "$cow_tmpfs"; then
 		cow_tmpfs="${cow_tmpfs}.$$"
 		if ! mkdir -p "$cow_tmpfs"; then
@@ -142,38 +168,24 @@ ramdisk_fallback() {
 			cow_tmpfs="/run/openslx"
 		fi
 	fi
-
-	local qcow_size_in_kb="$(( read_only_device_size / 2 ))"
-	local ram_size_in_kb="$(awk '/MemTotal/ {printf("%d\n", $2 )}' /proc/meminfo)"
-	modprobe dm-zero
-	# fill the qcow2 device with a zero device to make it larger than it is
-	dmsetup_create_noudevsync filler "0 $ram_size_in_kb zero"
-	echo "0 $read_only_device_size linear $read_only_device 0
-	$read_only_device_size $ram_size_in_kb linear /dev/mapper/filler 0" | dmsetup create bigger --noudevsync
-	dmsetup mknodes --noudevsync bigger
-
-	# Use the qcow size + ***************half************* the RAM as tmpfs size.
-	local cow_size="$(( qcow_size_in_kb + ( ram_size_in_kb / 2 ) ))"
-	if ! mount -t tmpfs tmpfs -o size="${cow_size}k" "$cow_tmpfs"; then
-		emergency_shell "Failed to prepare dedicated CoW tmpfs in $cow_tmpfs of size $cow_size."
+	if ! mount -t tmpfs cow-tmpfs -o size="$(( read_only_device_size / 2 ))k" "$cow_tmpfs"; then
+		echo "$0: Failed to mount tmpfs in '$cow_tmpfs' of size '$(( read_only_device_size / 2 ))'."
 	fi
 
+	# create sparse file there
 	local file="$(mktemp -u -p "$cow_tmpfs" dnbd_cow.XXX)"
-	if ! dd of="$file" seek="$cow_size" bs=1k count=0 &> /dev/null; then
+	if ! dd of="$file" seek="$(( read_only_device_size / 2 ))" bs=1k count=0 &> /dev/null; then
 		emergency_shell "Failed to allocate CoW file $file."
 	fi
-	writable_device="$(losetup --show --find "$file")"
-	read_only_device=/dev/mapper/bigger
-	read_only_device_size="$(( read_only_device_size + ram_size_in_kb ))"
-	cow_device_candidate="root"
+	declare -rg writable_device="$(losetup --show --find "$file")"
+	local cow_device_candidate="root"
 	while [ -b "/dev/mapper/$cow_device_candidate" ]; do
 		cow_device_candidate="root.$RANDOM"
 	done
 	if [ -z "$writable_device" ] || ! create_snapshot "$cow_device_candidate N"; then
 		emergency_shell "CRITICAL: failed to setup RAMdisk fallback."
-		exit 1
 	fi
-	finish_setup "$cow_device_candidate" "0" "$size"
+	finish_setup "$cow_device_candidate" "0" "$read_only_device_size"
 }
 
 # finish_setup <device> <type> [<size>]
-- 
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