1 files changed, 95 insertions, 0 deletions
diff --git a/lib/init/svc_tsort.c b/lib/init/svc_tsort.c
new file mode 100644
index 0000000..5f83fa0
--- /dev/null
+++ b/lib/init/svc_tsort.c
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * Copyright (C) 2018 - David Oberhollenzer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+#include <errno.h>
+
+#include "service.h"
+
+static bool has_dependencies(service_t *list, service_t *svc)
+{
+	const char *ptr;
+	int i;
+
+	while (list != NULL) {
+		for (ptr = svc->after, i = 0; i < svc->num_after; ++i) {
+			if (!strcmp(ptr, list->name))
+				return true;
+			ptr += strlen(ptr) + 1;
+		}
+
+		for (ptr = list->before, i = 0; i < list->num_before; ++i) {
+			if (!strcmp(ptr, svc->name))
+				return true;
+			ptr += strlen(ptr) + 1;
+		}
+
+		list = list->next;
+	}
+
+	return false;
+}
+
+service_t *svc_tsort(service_t *list)
+{
+	service_t *nl = NULL, *end = NULL;
+	service_t *svc, *prev;
+
+	while (list != NULL) {
+		/* remove first service without dependencies */
+		prev = NULL;
+		svc = list;
+
+		while (svc != NULL) {
+			if (has_dependencies(list, svc)) {
+				prev = svc;
+				svc = svc->next;
+			} else {
+				if (prev != NULL) {
+					prev->next = svc->next;
+				} else {
+					list = svc->next;
+				}
+				svc->next = NULL;
+				break;
+			}
+		}
+
+		/* cycle! */
+		if (svc == NULL) {
+			if (end == NULL) {
+				nl = list;
+			} else {
+				end->next = list;
+			}
+			errno = ELOOP;
+			break;
+		}
+
+		/* append to new list */
+		if (end == NULL) {
+			nl = end = svc;
+		} else {
+			end->next = svc;
+			end = svc;
+		}
+	}
+
+	return nl;
+}