safe_list: add a new linked list variant

Use this linked list implementation as a replacement for list.h if you
want to allow deleting arbitrary list entries from within one or more
recursive iterator calling context

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

1 files changed, 114 insertions, 0 deletions

diff --git a/safe_list.c b/safe_list.c
new file mode 100644
index 0000000..d9f211f
--- /dev/null
+++ b/safe_list.c
@@ -0,0 +1,114 @@
+/*
+ * safe_list - linked list protected against recursive iteration with deletes
+ *
+ * Copyright (C) 2013 Felix Fietkau <nbd@openwrt.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "safe_list.h"
+
+struct safe_list_iterator {
+	struct safe_list_iterator **head;
+	struct safe_list_iterator *next_i;
+	struct safe_list *next;
+};
+
+static void
+__safe_list_set_iterator(struct safe_list *list,
+			 struct safe_list_iterator *i)
+{
+	struct safe_list_iterator *next_i;
+	struct safe_list *next;
+
+	next = list_entry(list->list.next, struct safe_list, list);
+	next_i = next->i;
+
+	next->i = i;
+	i->next = next;
+	i->head = &next->i;
+
+	i->next_i = next_i;
+	if (next_i)
+		next_i->head = &i->next_i;
+}
+
+static void
+__safe_list_del_iterator(struct safe_list_iterator *i)
+{
+	*i->head = i->next_i;
+	if (i->next_i)
+		i->next_i->head = i->head;
+}
+
+static void
+__safe_list_move_iterator(struct safe_list *list,
+			  struct safe_list_iterator *i)
+{
+	__safe_list_del_iterator(i);
+	__safe_list_set_iterator(list, i);
+}
+
+int safe_list_for_each(struct safe_list *head,
+		       int (*cb)(void *ctx, struct safe_list *list),
+		       void *ctx)
+{
+	struct safe_list_iterator i;
+	struct safe_list *cur;
+	int ret = 0;
+
+	for (cur = list_entry(head->list.next, struct safe_list, list),
+	     __safe_list_set_iterator(cur, &i);
+	     cur != head;
+	     cur = i.next, __safe_list_move_iterator(cur, &i)) {
+		ret = cb(ctx, cur);
+		if (ret)
+			break;
+	}
+
+	__safe_list_del_iterator(&i);
+	return ret;
+}
+
+void safe_list_add(struct safe_list *list, struct safe_list *head)
+{
+	list->i = NULL;
+	list_add_tail(&list->list, &head->list);
+}
+
+void safe_list_del(struct safe_list *list)
+{
+	struct safe_list_iterator *i, *next_i, **tail;
+	struct safe_list *next;
+
+	next = list_entry(list->list.next, struct safe_list, list);
+	list_del(&list->list);
+
+	if (!list->i)
+		return;
+
+	next_i = next->i;
+	tail = &next->i;
+
+	for (i = list->i; i; i = i->next_i) {
+		tail = &i->next_i;
+		i->next = next;
+	}
+
+	next->i = list->i;
+	list->i->head = &next->i;
+	*tail = next_i;
+	next_i->head = tail;
+
+	list->i = NULL;
+}