conntrackd: add cthelper infrastructure (+ example FTP helper)

This patch adds the user-space helper infrastructure. It also
contains the implementation of the FTP helper in user-space.

There's one example file that you can use to configure conntrackd
as user-space connection tracking helper under:

 doc/helper/conntrackd.conf

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/stack.h b/include/stack.h
new file mode 100644
index 0000000..512a30f
--- /dev/null
+++ b/include/stack.h
@@ -0,0 +1,28 @@
+#ifndef _STACK_H_
+#define _STACK_H_
+
+#include "linux_list.h"
+
+struct stack {
+	struct list_head	list;
+	int			items;
+};
+
+static inline void stack_init(struct stack *s)
+{
+	INIT_LIST_HEAD(&s->list);
+}
+
+struct stack_item {
+	struct list_head	head;
+	int			type;
+	int			data_len;
+	char			data[0];
+};
+
+struct stack_item *stack_item_alloc(int type, size_t data_len);
+void stack_item_free(struct stack_item *e);
+void stack_item_push(struct stack *s, struct stack_item *e);
+struct stack_item *stack_item_pop(struct stack *s, int type);
+
+#endif