[slx-dmsetup] fix small ID44 / large filesystem

read the comments for the why :)

1 files changed, 13 insertions, 2 deletions

diff --git a/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device b/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device
index 29796d84..c0f6a274 100755
--- a/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device
+++ b/builder/modules.d/slx-dmsetup/scripts/dmsetup-slx-device
@@ -410,11 +410,22 @@ if [ -n "$thin_snapshot" ] || [ -n "$thin_volume" ]; then
 		# create thin-snapshot, use first one
 		read -r name crypt min max ignore <<< "$thin_snapshot"
 		# min/max was used for the pool data device, ignore it here!
-		if ! create_volume "$name 1 $writable_device_size $read_only_device"; then
+		# NOTE: the filesystem will most likely malfunction if the size of the
+		# thin-snapshot is smaller than what it was upon creation.
+		# As such, the size of the thin-snapshot can only be $writable_device_size
+		# if it is larger than $read_only_device_size, otherwise we should only
+		# use $read_only_device_size. While live-shrinking the filesystem might be
+		# an option, it is not supported throughout all fileystems (xfs can't).
+		if (( writable_device_size >= read_only_device_size )); then
+			thin_snapshot_size="$writable_device_size"
+		else
+			thin_snapshot_size="$read_only_device_size"
+		fi
+		if ! create_volume "$name 1 $thin_snapshot_size $read_only_device"; then
 			echo "Failed to create external snapshot for '$read_only_device'."
 			ramdisk_fallback
 		fi
-		finish_setup "$name" "1" "$writable_device_size"
+		finish_setup "$name" "1" "$thin_snapshot_size"
 	fi
 fi