--- /dev/null
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef LLIST_H
+#define LLIST_H
+/*
+ * Lock-less NULL terminated single linked list
+ *
+ * Cases where locking is not needed:
+ * If there are multiple producers and multiple consumers, llist_add can be
+ * used in producers and llist_del_all can be used in consumers simultaneously
+ * without locking. Also a single consumer can use llist_del_first while
+ * multiple producers simultaneously use llist_add, without any locking.
+ *
+ * Cases where locking is needed:
+ * If we have multiple consumers with llist_del_first used in one consumer, and
+ * llist_del_first or llist_del_all used in other consumers, then a lock is
+ * needed. This is because llist_del_first depends on list->first->next not
+ * changing, but without lock protection, there's no way to be sure about that
+ * if a preemption happens in the middle of the delete operation and on being
+ * preempted back, the list->first is the same as before causing the cmpxchg in
+ * llist_del_first to succeed. For example, while a llist_del_first operation
+ * is in progress in one consumer, then a llist_del_first, llist_add,
+ * llist_add (or llist_del_all, llist_add, llist_add) sequence in another
+ * consumer may cause violations.
+ *
+ * This can be summarized as follows:
+ *
+ * | add | del_first | del_all
+ * add | - | - | -
+ * del_first | | L | L
+ * del_all | | | -
+ *
+ * Where, a particular row's operation can happen concurrently with a column's
+ * operation, with "-" being no lock needed, while "L" being lock is needed.
+ *
+ * The list entries deleted via llist_del_all can be traversed with
+ * traversing function such as llist_for_each etc. But the list
+ * entries can not be traversed safely before deleted from the list.
+ * The order of deleted entries is from the newest to the oldest added
+ * one. If you want to traverse from the oldest to the newest, you
+ * must reverse the order by yourself before traversing.
+ *
+ * The basic atomic operation of this list is cmpxchg on long. On
+ * architectures that don't have NMI-safe cmpxchg implementation, the
+ * list can NOT be used in NMI handlers. So code that uses the list in
+ * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
+ *
+ * Copyright 2010,2011 Intel Corp.
+ * Author: Huang Ying <ying.huang@intel.com>
+ */
+
+#include <linux/atomic.h>
+#include <linux/kernel.h>
+
+struct llist_head {
+ struct llist_node *first;
+};
+
+struct llist_node {
+ struct llist_node *next;
+};
+
+#define LLIST_HEAD_INIT(name) { NULL }
+#define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name)
+
+/**
+ * init_llist_head - initialize lock-less list head
+ * @head: the head for your lock-less list
+ */
+static inline void init_llist_head(struct llist_head *list)
+{
+ list->first = NULL;
+}
+
+/**
+ * llist_entry - get the struct of this entry
+ * @ptr: the &struct llist_node pointer.
+ * @type: the type of the struct this is embedded in.
+ * @member: the name of the llist_node within the struct.
+ */
+#define llist_entry(ptr, type, member) \
+ container_of(ptr, type, member)
+
+/**
+ * member_address_is_nonnull - check whether the member address is not NULL
+ * @ptr: the object pointer (struct type * that contains the llist_node)
+ * @member: the name of the llist_node within the struct.
+ *
+ * This macro is conceptually the same as
+ * &ptr->member != NULL
+ * but it works around the fact that compilers can decide that taking a member
+ * address is never a NULL pointer.
+ *
+ * Real objects that start at a high address and have a member at NULL are
+ * unlikely to exist, but such pointers may be returned e.g. by the
+ * container_of() macro.
+ */
+#define member_address_is_nonnull(ptr, member) \
+ ((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0)
+
+/**
+ * llist_for_each - iterate over some deleted entries of a lock-less list
+ * @pos: the &struct llist_node to use as a loop cursor
+ * @node: the first entry of deleted list entries
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being deleted from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry. If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ */
+#define llist_for_each(pos, node) \
+ for ((pos) = (node); pos; (pos) = (pos)->next)
+
+/**
+ * llist_for_each_safe - iterate over some deleted entries of a lock-less list
+ * safe against removal of list entry
+ * @pos: the &struct llist_node to use as a loop cursor
+ * @n: another &struct llist_node to use as temporary storage
+ * @node: the first entry of deleted list entries
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being deleted from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry. If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ */
+#define llist_for_each_safe(pos, n, node) \
+ for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
+
+/**
+ * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
+ * @pos: the type * to use as a loop cursor.
+ * @node: the fist entry of deleted list entries.
+ * @member: the name of the llist_node with the struct.
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being removed from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry. If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ */
+#define llist_for_each_entry(pos, node, member) \
+ for ((pos) = llist_entry((node), typeof(*(pos)), member); \
+ member_address_is_nonnull(pos, member); \
+ (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
+
+/**
+ * llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type
+ * safe against removal of list entry
+ * @pos: the type * to use as a loop cursor.
+ * @n: another type * to use as temporary storage
+ * @node: the first entry of deleted list entries.
+ * @member: the name of the llist_node with the struct.
+ *
+ * In general, some entries of the lock-less list can be traversed
+ * safely only after being removed from list, so start with an entry
+ * instead of list head.
+ *
+ * If being used on entries deleted from lock-less list directly, the
+ * traverse order is from the newest to the oldest added entry. If
+ * you want to traverse from the oldest to the newest, you must
+ * reverse the order by yourself before traversing.
+ */
+#define llist_for_each_entry_safe(pos, n, node, member) \
+ for (pos = llist_entry((node), typeof(*pos), member); \
+ member_address_is_nonnull(pos, member) && \
+ (n = llist_entry(pos->member.next, typeof(*n), member), true); \
+ pos = n)
+
+/**
+ * llist_empty - tests whether a lock-less list is empty
+ * @head: the list to test
+ *
+ * Not guaranteed to be accurate or up to date. Just a quick way to
+ * test whether the list is empty without deleting something from the
+ * list.
+ */
+static inline bool llist_empty(const struct llist_head *head)
+{
+ return READ_ONCE(head->first) == NULL;
+}
+
+static inline struct llist_node *llist_next(struct llist_node *node)
+{
+ return node->next;
+}
+
+extern bool llist_add_batch(struct llist_node *new_first,
+ struct llist_node *new_last,
+ struct llist_head *head);
+/**
+ * llist_add - add a new entry
+ * @new: new entry to be added
+ * @head: the head for your lock-less list
+ *
+ * Returns true if the list was empty prior to adding this entry.
+ */
+static inline bool llist_add(struct llist_node *new, struct llist_head *head)
+{
+ return llist_add_batch(new, new, head);
+}
+
+/**
+ * llist_del_all - delete all entries from lock-less list
+ * @head: the head of lock-less list to delete all entries
+ *
+ * If list is empty, return NULL, otherwise, delete all entries and
+ * return the pointer to the first entry. The order of entries
+ * deleted is from the newest to the oldest added one.
+ */
+static inline struct llist_node *llist_del_all(struct llist_head *head)
+{
+ return xchg(&head->first, NULL);
+}
+
+extern struct llist_node *llist_del_first(struct llist_head *head);
+
+struct llist_node *llist_reverse_order(struct llist_node *head);
+
+#endif /* LLIST_H */
projects / bcachefs-tools-debian / blobdiff