helpers: Create helper link_or_rename()

Trying to link and on an error, rename the file was used more than
once, so unifying in a helper function.

src/fullfile.c

@@ -27,7 +27,6 @@
 
 static struct list *download_loop(struct list *files, bool free_list)
 {
-	int ret;
 	struct list *iter;
 	unsigned int complete = 0;
 	unsigned int list_length = list_len(files);
@@ -55,13 +54,9 @@ static struct list *download_loop(struct list *files, bool free_list)
 			string_or_die(&url, "%s/%i/files/%s.tar", MIX_STATE_DIR, file->last_change, file->hash);
 			string_or_die(&file->staging, "%s/download/.%s.tar", state_dir, file->hash);
 
-			ret = link(url, file->staging);
-			/* Try doing a regular rename if hardlink fails */
-			if (ret) {
-				if (rename(url, file->staging) != 0) {
-					fprintf(stderr, "Failed to copy local mix file: %s\n", file->staging);
-					continue;
-				}
+			if (link_or_rename(url, file->staging) != 0) {
+				fprintf(stderr, "Failed to copy local mix file: %s\n", file->staging);
+				continue;
 			}
 			untar_full_download(file);
 			free_string(&url);

src/helpers.c

@@ -941,3 +941,15 @@ bool on_new_format(void)
 	 * different from the one we started on. */
 	return !is_compatible_format(res);
 }
+
+/* Try to create a link to a file. If it fails, rename it.
+ * Return 0 on success or an error code on errors.*/
+int link_or_rename(const char *orig, const char *dest)
+{
+	/* Try doing a regular rename if hardlink fails */
+	if (link(orig, dest) != 0) {
+		return rename(orig, dest);
+	}
+
+	return 0;
+}

src/manifest.c

@@ -489,11 +489,7 @@ static int retrieve_manifests(int current, int version, char *component, struct
 	if (is_mix) {
 		string_or_die(&filename, "%s/%i/Manifest.%s.tar", state_dir, version, component);
 		string_or_die(&url, "%s/%i/Manifest.%s.tar", basedir, version, component);
-		ret = link(url, filename);
-		/* Try doing a regular rename if hardlink fails */
-		if (ret) {
-			ret = rename(url, filename);
-		}
+		ret = link_or_rename(url, filename);
 		/* If rename fails, we try again below with curl to the contenurl */
 		if (ret == 0) {
 			goto untar;

src/swupd.h

@@ -383,6 +383,7 @@ extern int list_installable_bundles();
 extern int install_bundles_frontend(char **bundles);
 extern int add_subscriptions(struct list *bundles, struct list **subs, int current_version, struct manifest *mom, bool find_all, int recursion);
 int list_local_bundles();
+extern int link_or_rename(const char *orig, const char *dest);
 
 /* telemetry.c */
 typedef enum telem_prio_t {