headers: list.h -- Add hlist helpers

hlist is suitable for hash operations so
extent list.h code. I need it for converter
and this allow me to reuse this header.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/list.h

@@ -283,4 +283,141 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_safe_reset_next(pos, n, member)				\
 	n = list_entry(pos->member.next, typeof(*pos), member)
 
+/*
+ * Double linked lists with a single pointer list head.
+ */
+
+struct hlist_head {
+	struct hlist_node *first;
+};
+
+struct hlist_node {
+	struct hlist_node *next, **pprev;
+};
+
+#define HLIST_HEAD_INIT		{ .first = NULL }
+#define HLIST_HEAD(name)	struct hlist_head name = {  .first = NULL }
+#define INIT_HLIST_HEAD(ptr)	((ptr)->first = NULL)
+
+static inline void INIT_HLIST_NODE(struct hlist_node *h)
+{
+	h->next = NULL;
+	h->pprev = NULL;
+}
+
+static inline int hlist_unhashed(const struct hlist_node *h)
+{
+	return !h->pprev;
+}
+
+static inline int hlist_empty(const struct hlist_head *h)
+{
+	return !h->first;
+}
+
+static inline void __hlist_del(struct hlist_node *n)
+{
+	struct hlist_node *next = n->next;
+	struct hlist_node **pprev = n->pprev;
+	*pprev = next;
+	if (next)
+		next->pprev = pprev;
+}
+
+static inline void hlist_del(struct hlist_node *n)
+{
+	__hlist_del(n);
+	n->next = LIST_POISON1;
+	n->pprev = LIST_POISON2;
+}
+
+static inline void hlist_del_init(struct hlist_node *n)
+{
+	if (!hlist_unhashed(n)) {
+		__hlist_del(n);
+		INIT_HLIST_NODE(n);
+	}
+}
+
+static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
+{
+	struct hlist_node *first = h->first;
+	n->next = first;
+	if (first)
+		first->pprev = &n->next;
+	h->first = n;
+	n->pprev = &h->first;
+}
+
+/* next must be != NULL */
+static inline void hlist_add_before(struct hlist_node *n,
+				    struct hlist_node *next)
+{
+	n->pprev = next->pprev;
+	n->next = next;
+	next->pprev = &n->next;
+	*(n->pprev) = n;
+}
+
+static inline void hlist_add_after(struct hlist_node *n,
+				   struct hlist_node *next)
+{
+	next->next = n->next;
+	n->next = next;
+	next->pprev = &n->next;
+
+	if(next->next)
+		next->next->pprev  = &next->next;
+}
+
+/* after that we'll appear to be on some hlist and hlist_del will work */
+static inline void hlist_add_fake(struct hlist_node *n)
+{
+	n->pprev = &n->next;
+}
+
+/*
+ * Move a list from one list head to another. Fixup the pprev
+ * reference of the first entry if it exists.
+ */
+static inline void hlist_move_list(struct hlist_head *old,
+				   struct hlist_head *new)
+{
+	new->first = old->first;
+	if (new->first)
+		new->first->pprev = &new->first;
+	old->first = NULL;
+}
+
+#define hlist_entry(ptr, type, member) container_of(ptr,type,member)
+
+#define hlist_for_each(pos, head)						\
+	for (pos = (head)->first; pos ; pos = pos->next)
+
+#define hlist_for_each_safe(pos, n, head)					\
+	for (pos = (head)->first; pos && ({ n = pos->next; 1; });		\
+	     pos = n)
+
+#define hlist_entry_safe(ptr, type, member)					\
+	(ptr) ? hlist_entry(ptr, type, member) : NULL
+
+#define hlist_for_each_entry(pos, head, member)					\
+	for (pos = hlist_entry_safe((head)->first, typeof(*(pos)), member);	\
+	     pos;								\
+	     pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))
+
+#define hlist_for_each_entry_continue(pos, member)				\
+	for (pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member);\
+	     pos;								\
+	     pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))
+
+#define hlist_for_each_entry_from(pos, member)					\
+	for (; pos;								\
+	     pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))
+
+#define hlist_for_each_entry_safe(pos, n, head, member)				\
+	for (pos = hlist_entry_safe((head)->first, typeof(*pos), member);	\
+	     pos && ({ n = pos->member.next; 1; });				\
+	     pos = hlist_entry_safe(n, typeof(*pos), member))
+
 #endif /* __CR_LIST_H__ */