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 /* 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/container_of.h>
 #include <linux/stddef.h>
 #include <linux/types.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);
 
 static inline bool __llist_add_batch(struct llist_node *new_first,
                      struct llist_node *new_last,
                      struct llist_head *head)
 {
     new_last->next = head->first;
     head->first = new_first;
     return new_last->next == NULL;
 }
 
 /**
  * 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);
 }
 
 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);
 }
 
 static inline struct llist_node *__llist_del_all(struct llist_head *head)
 {
     struct llist_node *first = head->first;
 
     head->first = NULL;
     return first;
 }
 
 extern struct llist_node *llist_del_first(struct llist_head *head);
 
 struct llist_node *llist_reverse_order(struct llist_node *head);
 
 #endif /* LLIST_H */

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