added zstd compression option with `SQUASHFS=zstd`

features.in/stage2/stage1/scripts.d/03-test-kernel

@@ -6,6 +6,7 @@ CONFIGS=/boot/config-*
 GZ_OPTS="-comp gzip"
 XZ_OPTS="-comp xz"
 LZO_OPTS="-comp lzo"
+ZSTD_OPTS="-comp zstd -Xcompression-level 11"
 
 verbose() { [ -z "$GLOBAL_VERBOSE" ] || echo "** $@" >&2; }
 fatal() { echo "** error: $@" >&2; exit 1; }
@@ -37,6 +38,12 @@ options()
 {
 	# squashfs options: not really neccessary but better than none
 	# NB: this config file should be carried over into install2
+
+	if [ "$GLOBAL_SQUASHFS" = "zstd" ] && configured "SQUASHFS_ZSTD=y"; then
+		verbose "using modern zstd compression"
+		echo "$ZSTD_OPTS"
+		return 0
+	fi
 	if [ "$GLOBAL_SQUASHFS" != "fast" ] && configured "SQUASHFS_XZ=y"; then
 		# NB: the decompression filter overhead might hurt
 		# NB: there are arm, powerpc and some other filters too