FreeBSD/Linux Kernel Cross Reference
sys/lib/llist.c

     /*
      * 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>
     *
     * This program is free software; you can redistribute it and/or
     * modify it under the terms of the GNU General Public License version
     * 2 as published by the Free Software Foundation;
     *
     * This program is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
     */
    #include <linux/kernel.h>
    #include <linux/export.h>
    #include <linux/interrupt.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 *entry, *old_entry;
    
            entry = head->first;
            for (;;) {
                    old_entry = entry;
                    new_last->next = entry;
                    entry = cmpxchg(&head->first, old_entry, new_first);
                    if (entry == old_entry)
                            break;
            }
    
            return old_entry == NULL;
    }
    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 = head->first;
            for (;;) {
                    if (entry == NULL)
                            return NULL;
                    old_entry = entry;
                    next = entry->next;
                    entry = cmpxchg(&head->first, old_entry, next);
                    if (entry == old_entry)
                            break;
            }
    
            return entry;
    }
    EXPORT_SYMBOL_GPL(llist_del_first);

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