scripts: generate SHA256 manifest lines in addition to SHA512

The current autoupdater will only respect the last line for a given model
name, so we can add SHA256 checksums as long as they occur before the
corresponding SHA512 line.

scripts/generate_manifest.sh

@@ -20,6 +20,7 @@ generate_line() {
 	local model="$1"
 	local file="$2"
 
+	[ ! -e "${GLUON_IMAGEDIR}/sysupgrade/$file" ] || echo "$model" "$GLUON_RELEASE" "$(scripts/sha256sum.sh "${GLUON_IMAGEDIR}/sysupgrade/$file")" "$file"
 	[ ! -e "${GLUON_IMAGEDIR}/sysupgrade/$file" ] || echo "$model" "$GLUON_RELEASE" "$(scripts/sha512sum.sh "${GLUON_IMAGEDIR}/sysupgrade/$file")" "$file"
 }
 

scripts/sha256sum.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+check_command() {
+	which "$1" >/dev/null 2>&1
+}
+
+if check_command sha256sum; then
+	ret="$(sha256sum "$@")"
+elif check_command shasum; then
+	ret="$(shasum -a 256 "$@")"
+elif check_command cksum; then
+	ret="$(cksum -q -a sha256 "$@")"
+else
+	echo "$0: no suitable sha256sum implementation was found" >&2
+	exit 1
+fi
+
+[ "$?" -eq 0 ] || exit 1
+
+echo "$ret" | awk '{ print $1 }'