// SPDX-License-Identifier: GPL-2.0-only

  /*
   * Lock-less NULL terminated single linked list
   *
   * 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/kernel.h>

  #include <linux/export.h>

  #include <linux/llist.h>

  
  /**

   * llist_add_batch - add several linked entries in batch
   * @new_first:	first entry in batch to be added
   * @new_last:	last entry in batch to be added
   * @head:	the head for your lock-less list

   *
   * Return whether list is empty before adding.

   */

  bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,

  		     struct llist_head *head)
  {

  	struct llist_node *first;

  	do {

  		new_last->next = first = READ_ONCE(head->first);

  	} while (cmpxchg(&head->first, first, new_first) != first);

  	return !first;

  }
  EXPORT_SYMBOL_GPL(llist_add_batch);
  
  /**
   * llist_del_first - delete the first entry of lock-less list
   * @head:	the head for your lock-less list
   *
   * If list is empty, return NULL, otherwise, return the first entry
   * deleted, this is the newest added one.
   *
   * Only one llist_del_first user can be used simultaneously with
   * multiple llist_add users without lock.  Because otherwise
   * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
   * llist_add) sequence in another user may change @head->first->next,
   * but keep @head->first.  If multiple consumers are needed, please
   * use llist_del_all or use lock between consumers.
   */
  struct llist_node *llist_del_first(struct llist_head *head)
  {
  	struct llist_node *entry, *old_entry, *next;

  	entry = smp_load_acquire(&head->first);

  	for (;;) {

  		if (entry == NULL)
  			return NULL;
  		old_entry = entry;

  		next = READ_ONCE(entry->next);

  		entry = cmpxchg(&head->first, old_entry, next);
  		if (entry == old_entry)
  			break;

  	}

  
  	return entry;
  }
  EXPORT_SYMBOL_GPL(llist_del_first);

  
  /**
   * llist_reverse_order - reverse order of a llist chain
   * @head:	first item of the list to be reversed
   *

   * Reverse the order of a chain of llist entries and return the

   * new first entry.
   */
  struct llist_node *llist_reverse_order(struct llist_node *head)
  {
  	struct llist_node *new_head = NULL;
  
  	while (head) {
  		struct llist_node *tmp = head;
  		head = head->next;
  		tmp->next = new_head;
  		new_head = tmp;
  	}
  
  	return new_head;
  }
  EXPORT_SYMBOL_GPL(llist_reverse_order);