Add basic check for format number validity

Because the intention is for swupd format numbers to either remain the
same between LAST_VER and current, or to increase as part of a format
bump, this leaves the remaining undesirable case.

Add a basic check to make sure the format never decreases, and add a
functional test.

Signed-off-by: Patrick McCarty <patrick.mccarty@intel.com>

Makefile.am

@@ -110,6 +110,7 @@ dist_check_SCRIPTS = \
 	test/functional/basic/test.bats \
 	test/functional/delete-no-version-bump/test.bats \
 	test/functional/file-name-blacklisted/test.bats \
+	test/functional/format-no-decrement/test.bats \
 	test/functional/full-run-delta/test.bats \
 	test/functional/full-run/test.bats \
 	test/functional/fullfiles/test.bats \

src/create_update.c

@@ -340,6 +340,17 @@ int main(int argc, char **argv)
 
 	/* Step 2: Make a manifest for the os-core set */
 	old_MoM = manifest_from_file(current_version, "MoM");
+
+	/* Verify that the new format is not older than the previous format. It
+	 * never makes sense to decrease the format number for the next build. */
+	if (format < old_MoM->format) {
+		LOG(NULL, "", "Current format (%llu) must be greater than or equal to previous format (%llu). Exiting",
+		    format, old_MoM->format);
+		printf("Current format (%llu) must be greater than or equal to previous format (%llu). Exiting\n",
+		       format, old_MoM->format);
+		goto exit;
+	}
+
 	new_MoM = alloc_manifest(newversion, "MoM");
 	old_core = manifest_from_file(manifest_subversion(old_MoM, "os-core"), "os-core");
 	new_core = sub_manifest_from_directory("os-core", newversion);

test/functional/format-no-decrement/test.bats

@@ -0,0 +1,35 @@
+#!/usr/bin/env bats
+
+# common functions
+load "../swupdlib"
+
+setup() {
+  clean_test_dir
+  init_test_dir
+
+  init_server_ini
+  set_latest_ver 0
+  init_groups_ini os-core
+
+  set_os_release 10 os-core
+  track_bundle 10 os-core
+  set_os_release 20 os-core
+  track_bundle 20 os-core
+
+  gen_file_plain 10 os-core foo
+  gen_file_plain 10 os-core bar
+  gen_file_plain 20 os-core foo
+  gen_file_plain 20 os-core baz
+}
+
+@test "ensure format numbers cannot be decremented" {
+  sudo $CREATE_UPDATE --osversion 10 --statedir $DIR --format 3
+  set_latest_ver 10
+
+  # Now, decrement the format number. Should result in an EXIT_FAILURE.
+  run sudo $CREATE_UPDATE --osversion 20 --statedir $DIR --format 2
+  echo "$output"
+  [ $status -eq 1 ]
+}
+
+# vi: ft=sh ts=8 sw=2 sts=2 et tw=80