1 files changed, 145 insertions, 0 deletions
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
new file mode 100644
index 000000000..fa6e8471b
--- /dev/null
+++ b/include/linux/list_nulls.h
@@ -0,0 +1,145 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_LIST_NULLS_H
+#define _LINUX_LIST_NULLS_H
+
+#include <linux/poison.h>
+#include <linux/const.h>
+
+/*
+ * Special version of lists, where end of list is not a NULL pointer,
+ * but a 'nulls' marker, which can have many different values.
+ * (up to 2^31 different values guaranteed on all platforms)
+ *
+ * In the standard hlist, termination of a list is the NULL pointer.
+ * In this special 'nulls' variant, we use the fact that objects stored in
+ * a list are aligned on a word (4 or 8 bytes alignment).
+ * We therefore use the last significant bit of 'ptr' :
+ * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
+ * Set to 0 : This is a pointer to some object (ptr)
+ */
+
+struct hlist_nulls_head {
+	struct hlist_nulls_node *first;
+};
+
+struct hlist_nulls_node {
+	struct hlist_nulls_node *next, **pprev;
+};
+#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
+#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
+	((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
+
+#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
+
+#define hlist_nulls_entry_safe(ptr, type, member) \
+	({ typeof(ptr) ____ptr = (ptr); \
+	   !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
+	})
+/**
+ * ptr_is_a_nulls - Test if a ptr is a nulls
+ * @ptr: ptr to be tested
+ *
+ */
+static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
+{
+	return ((unsigned long)ptr & 1);
+}
+
+/**
+ * get_nulls_value - Get the 'nulls' value of the end of chain
+ * @ptr: end of chain
+ *
+ * Should be called only if is_a_nulls(ptr);
+ */
+static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
+{
+	return ((unsigned long)ptr) >> 1;
+}
+
+/**
+ * hlist_nulls_unhashed - Has node been removed and reinitialized?
+ * @h: Node to be checked
+ *
+ * Not that not all removal functions will leave a node in unhashed state.
+ * For example, hlist_del_init_rcu() leaves the node in unhashed state,
+ * but hlist_nulls_del() does not.
+ */
+static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
+{
+	return !h->pprev;
+}
+
+/**
+ * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
+ * @h: Node to be checked
+ *
+ * Not that not all removal functions will leave a node in unhashed state.
+ * For example, hlist_del_init_rcu() leaves the node in unhashed state,
+ * but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
+ * function may be used locklessly.
+ */
+static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
+{
+	return !READ_ONCE(h->pprev);
+}
+
+static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
+{
+	return is_a_nulls(READ_ONCE(h->first));
+}
+
+static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
+					struct hlist_nulls_head *h)
+{
+	struct hlist_nulls_node *first = h->first;
+
+	n->next = first;
+	WRITE_ONCE(n->pprev, &h->first);
+	h->first = n;
+	if (!is_a_nulls(first))
+		WRITE_ONCE(first->pprev, &n->next);
+}
+
+static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
+{
+	struct hlist_nulls_node *next = n->next;
+	struct hlist_nulls_node **pprev = n->pprev;
+
+	WRITE_ONCE(*pprev, next);
+	if (!is_a_nulls(next))
+		WRITE_ONCE(next->pprev, pprev);
+}
+
+static inline void hlist_nulls_del(struct hlist_nulls_node *n)
+{
+	__hlist_nulls_del(n);
+	WRITE_ONCE(n->pprev, LIST_POISON2);
+}
+
+/**
+ * hlist_nulls_for_each_entry	- iterate over list of given type
+ * @tpos:	the type * to use as a loop cursor.
+ * @pos:	the &struct hlist_node to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the hlist_node within the struct.
+ *
+ */
+#define hlist_nulls_for_each_entry(tpos, pos, head, member)		       \
+	for (pos = (head)->first;					       \
+	     (!is_a_nulls(pos)) &&					       \
+		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
+	     pos = pos->next)
+
+/**
+ * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
+ * @tpos:	the type * to use as a loop cursor.
+ * @pos:	the &struct hlist_node to use as a loop cursor.
+ * @member:	the name of the hlist_node within the struct.
+ *
+ */
+#define hlist_nulls_for_each_entry_from(tpos, pos, member)	\
+	for (; (!is_a_nulls(pos)) && 				\
+		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
+	     pos = pos->next)
+
+#endif