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From: Konstantin Khlebnikov on 8 Jul 2010 04:50
Intoduce slist -- singly-linked circular list.
Usable for implementing Stacks and Sets.

Struct slist_head uses twice less memory than nornal doubly-linked list_head.

slist able to freely add and delete entries only at head
or while safe-iterating: slist_for_each_entry_safe() provide pointer to
previous entry, it usable to remove current entry or add new entry before it.

Signed-off-by: Konstantin Khlebnikov <khlebnikov(a)openvz.org>
---
include/linux/list.h | 194 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 194 insertions(+), 0 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index 6a6e9d3..691d37b 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -809,4 +809,198 @@ static inline void hlist_move_list(struct hlist_head *old,
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
pos = n)

+/*
+ * Simple sindly-linked list implementation.
+ */
+
+struct slist_head {
+ struct slist_head *next;
+};
+
+#define SLIST_HEAD_INIT(name) { .next = &(name) }
+
+#define SLIST_HEAD(name) \
+ struct slist_head name = SLIST_HEAD_INIT(name)
+
+static inline void INIT_SLIST_HEAD(struct slist_head *list)
+{
+ list->next = list;
+}
+
+/**
+ * slist_empty - tests whether a list is empty
+ * @head: the list to test.
+ */
+static inline bool slist_empty(const struct slist_head *head)
+{
+ return head->next == head;
+}
+
+/**
+ * slist_add - add a new entry
+ * @entry: new entry to be added
+ * @prev: list head to add it after
+ *
+ * Insert a new entry after the specified head.
+ */
+static inline void slist_add(struct slist_head *entry, struct slist_head *prev)
+{
+ entry->next = prev->next;
+ prev->next = entry;
+}
+
+/**
+ * slist_del - deletes entry from list.
+ * @entry: the element to delete from the list.
+ * @prev: previous entry in the list, list head for first entry.
+ *
+ * Note: slist_empty() on entry does not return true after this, the entry is
+ * in an undefined state.
+ */
+static inline void slist_del(struct slist_head *entry,
+ struct slist_head *prev)
+{
+ prev->next = entry->next;
+ entry->next = LIST_POISON1;
+}
+
+/**
+ * slist_del_init - deletes entry from list and reinitialize it.
+ * @entry: the element to delete from the list.
+ * @prev: previous entry in the list, list head for first entry.
+ */
+static inline void slist_del_init(struct slist_head *entry,
+ struct slist_head *prev)
+{
+ slist_del(entry, prev);
+ INIT_SLIST_HEAD(entry);
+}
+
+/**
+ * __slist_splice - add entries chain into list
+ * @first: chain first entry
+ * @last: chain last entry
+ * @prev: place to insert chain
+ */
+static inline void __slist_splice(struct slist_head *first,
+ struct slist_head *last,
+ struct slist_head *prev)
+{
+ last->next = prev->next;
+ prev->next = first;
+}
+
+/**
+ * slist_entry - get the struct for this entry
+ * @ptr: the &struct slist_head pointer.
+ * @type: the type of the struct this is embedded in.
+ * @member: the name of the list_struct within the struct.
+ */
+#define slist_entry(ptr, type, member) \
+ container_of(ptr, type, member)
+
+/**
+ * slist_first_entry - get the first element from a list
+ * @head: the list head to take the element from.
+ * @type: the type of the struct this is embedded in.
+ * @member: the name of the slist_struct within the struct.
+ *
+ * Note, that list is expected to be not empty.
+ */
+#define slist_first_entry(head, type, member) \
+ slist_entry((head)->next, type, member)
+
+/**
+ * slist_peek_entry - check is list non-empty and retrieve list first entry,
+ * @ptr pointer to strict * there to save result
+ * @head: the struct slist_head pointer.
+ * @member: the name of the slist_struct within the struct.
+ *
+ * Return true if list was not empty and @ptr is changed
+ */
+#define slist_peek_entry(ptr, head, member) ({ \
+ bool __empty = slist_empty(head); \
+ if (!__empty) { \
+ *(ptr) = slist_first_entry(head, typeof(**(ptr)), member); \
+ } (!__empty); })
+
+/**
+ * slist_pop_entry - check is list non-empty, retrieve and delete first entry,
+ * @ptr pointer to strict * there to save result
+ * @head: the struct slist_head pointer.
+ * @member: the name of the slist_struct within the struct.
+ *
+ * Return true if list was not empty and @ptr is changed
+ */
+#define slist_pop_entry(ptr, head, member) ({ \
+ bool __empty = slist_empty(head); \
+ if (!__empty) { \
+ *(ptr) = slist_first_entry(head, typeof(**(ptr)), member); \
+ slist_del(&(*(ptr))->member, head); \
+ } (!__empty); })
+
+/**
+ * slist_pop_init_entry - delete, reinitialize and return list first entry,
+ * @ptr pointer to strict * there to save result
+ * @head: the struct slist_head pointer.
+ * @member: the name of the slist_struct within the struct.
+ *
+ * Return true if list was not empty and @ptr is changed
+ */
+#define slist_pop_init_entry(ptr, head, member) ({ \
+ bool __empty = slist_empty(head); \
+ if (!__empty) { \
+ *(ptr) = slist_first_entry(head, typeof(**(ptr)), member); \
+ slist_del_init(&(*(ptr))->member, head); \
+ } (!__empty); })
+
+/**
+ * slist_for_each - iterate over a list
+ * @pos: the &struct list_head to use as a loop cursor.
+ * @head: the head for your list.
+ */
+#define slist_for_each(pos, head) \
+ for (pos = (head)->next; prefetch(pos->next), pos != (head); \
+ pos = pos->next)
+
+/**
+ * slist_for_each_safe - iterate over a list safe against removal of list entry
+ * @pos: the &struct slist_head to use as a loop cursor.
+ * @prev: pointer to struct slist_head to store precursor.
+ * @n: another &struct list_head to use as temporary storage
+ * @head: the head for your list.
+ */
+#define slist_for_each_safe(pos, prev, n, head) \
+ for (prev = (head), pos = (head)->next, n = pos->next; \
+ prefetch(pos->next), pos != (head); \
+ prev = (prev->next == n) ? prev : pos, pos = n, n = pos->next)
+
+/**
+ * slist_for_each_entry - iterate over list of given type
+ * @pos: the type * to use as a loop cursor.
+ * @head: the head for your list.
+ * @member: the name of the list_struct within the struct.
+ */
+#define slist_for_each_entry(pos, head, member) \
+ for (pos = slist_entry((head)->next, typeof(*pos), member); \
+ prefetch(pos->member.next), &pos->member != (head); \
+ pos = slist_entry(pos->member.next, typeof(*pos), member))
+
+/**
+ * slist_for_each_entry_safe - iterate over list of given type
+ * safe against removal of list entry
+ * @pos: the type * to use as a loop cursor.
+ * @prev: pointer to struct slist_head to store precursor.
+ * @n: another type * to use as temporary storage
+ * @head: the head for your list.
+ * @member: the name of the list_struct within the struct.
+ */
+#define slist_for_each_entry_safe(pos, prev, n, head, member) \
+ for (prev = &(head)->member, \
+ pos = slist_entry((head)->next, typeof(*pos), member), \
+ n = slist_entry(pos->member.next, typeof(*pos), member); \
+ prefetch(pos->member.next), &pos->member != (head); \
+ prev = (prev->next == &n->member) ? prev : &pos->member, \
+ pos = n, n = slist_entry(n->member.next, typeof(*n), member))
+
#endif

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