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

     /*
      * klist.c - Routines for manipulating klists.
      *
      * Copyright (C) 2005 Patrick Mochel
      *
      * This file is released under the GPL v2.
      *
      * This klist interface provides a couple of structures that wrap around
      * struct list_head to provide explicit list "head" (struct klist) and list
     * "node" (struct klist_node) objects. For struct klist, a spinlock is
     * included that protects access to the actual list itself. struct
     * klist_node provides a pointer to the klist that owns it and a kref
     * reference count that indicates the number of current users of that node
     * in the list.
     *
     * The entire point is to provide an interface for iterating over a list
     * that is safe and allows for modification of the list during the
     * iteration (e.g. insertion and removal), including modification of the
     * current node on the list.
     *
     * It works using a 3rd object type - struct klist_iter - that is declared
     * and initialized before an iteration. klist_next() is used to acquire the
     * next element in the list. It returns NULL if there are no more items.
     * Internally, that routine takes the klist's lock, decrements the
     * reference count of the previous klist_node and increments the count of
     * the next klist_node. It then drops the lock and returns.
     *
     * There are primitives for adding and removing nodes to/from a klist.
     * When deleting, klist_del() will simply decrement the reference count.
     * Only when the count goes to 0 is the node removed from the list.
     * klist_remove() will try to delete the node from the list and block until
     * it is actually removed. This is useful for objects (like devices) that
     * have been removed from the system and must be freed (but must wait until
     * all accessors have finished).
     */
    
    #include <linux/klist.h>
    #include <linux/export.h>
    #include <linux/sched.h>
    
    /*
     * Use the lowest bit of n_klist to mark deleted nodes and exclude
     * dead ones from iteration.
     */
    #define KNODE_DEAD              1LU
    #define KNODE_KLIST_MASK        ~KNODE_DEAD
    
    static struct klist *knode_klist(struct klist_node *knode)
    {
            return (struct klist *)
                    ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
    }
    
    static bool knode_dead(struct klist_node *knode)
    {
            return (unsigned long)knode->n_klist & KNODE_DEAD;
    }
    
    static void knode_set_klist(struct klist_node *knode, struct klist *klist)
    {
            knode->n_klist = klist;
            /* no knode deserves to start its life dead */
            WARN_ON(knode_dead(knode));
    }
    
    static void knode_kill(struct klist_node *knode)
    {
            /* and no knode should die twice ever either, see we're very humane */
            WARN_ON(knode_dead(knode));
            *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
    }
    
    /**
     * klist_init - Initialize a klist structure.
     * @k: The klist we're initializing.
     * @get: The get function for the embedding object (NULL if none)
     * @put: The put function for the embedding object (NULL if none)
     *
     * Initialises the klist structure.  If the klist_node structures are
     * going to be embedded in refcounted objects (necessary for safe
     * deletion) then the get/put arguments are used to initialise
     * functions that take and release references on the embedding
     * objects.
     */
    void klist_init(struct klist *k, void (*get)(struct klist_node *),
                    void (*put)(struct klist_node *))
    {
            INIT_LIST_HEAD(&k->k_list);
            spin_lock_init(&k->k_lock);
            k->get = get;
            k->put = put;
    }
    EXPORT_SYMBOL_GPL(klist_init);
    
    static void add_head(struct klist *k, struct klist_node *n)
    {
            spin_lock(&k->k_lock);
            list_add(&n->n_node, &k->k_list);
            spin_unlock(&k->k_lock);
   }
   
   static void add_tail(struct klist *k, struct klist_node *n)
   {
           spin_lock(&k->k_lock);
           list_add_tail(&n->n_node, &k->k_list);
           spin_unlock(&k->k_lock);
   }
   
   static void klist_node_init(struct klist *k, struct klist_node *n)
   {
           INIT_LIST_HEAD(&n->n_node);
           kref_init(&n->n_ref);
           knode_set_klist(n, k);
           if (k->get)
                   k->get(n);
   }
   
   /**
    * klist_add_head - Initialize a klist_node and add it to front.
    * @n: node we're adding.
    * @k: klist it's going on.
    */
   void klist_add_head(struct klist_node *n, struct klist *k)
   {
           klist_node_init(k, n);
           add_head(k, n);
   }
   EXPORT_SYMBOL_GPL(klist_add_head);
   
   /**
    * klist_add_tail - Initialize a klist_node and add it to back.
    * @n: node we're adding.
    * @k: klist it's going on.
    */
   void klist_add_tail(struct klist_node *n, struct klist *k)
   {
           klist_node_init(k, n);
           add_tail(k, n);
   }
   EXPORT_SYMBOL_GPL(klist_add_tail);
   
   /**
    * klist_add_after - Init a klist_node and add it after an existing node
    * @n: node we're adding.
    * @pos: node to put @n after
    */
   void klist_add_after(struct klist_node *n, struct klist_node *pos)
   {
           struct klist *k = knode_klist(pos);
   
           klist_node_init(k, n);
           spin_lock(&k->k_lock);
           list_add(&n->n_node, &pos->n_node);
           spin_unlock(&k->k_lock);
   }
   EXPORT_SYMBOL_GPL(klist_add_after);
   
   /**
    * klist_add_before - Init a klist_node and add it before an existing node
    * @n: node we're adding.
    * @pos: node to put @n after
    */
   void klist_add_before(struct klist_node *n, struct klist_node *pos)
   {
           struct klist *k = knode_klist(pos);
   
           klist_node_init(k, n);
           spin_lock(&k->k_lock);
           list_add_tail(&n->n_node, &pos->n_node);
           spin_unlock(&k->k_lock);
   }
   EXPORT_SYMBOL_GPL(klist_add_before);
   
   struct klist_waiter {
           struct list_head list;
           struct klist_node *node;
           struct task_struct *process;
           int woken;
   };
   
   static DEFINE_SPINLOCK(klist_remove_lock);
   static LIST_HEAD(klist_remove_waiters);
   
   static void klist_release(struct kref *kref)
   {
           struct klist_waiter *waiter, *tmp;
           struct klist_node *n = container_of(kref, struct klist_node, n_ref);
   
           WARN_ON(!knode_dead(n));
           list_del(&n->n_node);
           spin_lock(&klist_remove_lock);
           list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
                   if (waiter->node != n)
                           continue;
   
                   waiter->woken = 1;
                   mb();
                   wake_up_process(waiter->process);
                   list_del(&waiter->list);
           }
           spin_unlock(&klist_remove_lock);
           knode_set_klist(n, NULL);
   }
   
   static int klist_dec_and_del(struct klist_node *n)
   {
           return kref_put(&n->n_ref, klist_release);
   }
   
   static void klist_put(struct klist_node *n, bool kill)
   {
           struct klist *k = knode_klist(n);
           void (*put)(struct klist_node *) = k->put;
   
           spin_lock(&k->k_lock);
           if (kill)
                   knode_kill(n);
           if (!klist_dec_and_del(n))
                   put = NULL;
           spin_unlock(&k->k_lock);
           if (put)
                   put(n);
   }
   
   /**
    * klist_del - Decrement the reference count of node and try to remove.
    * @n: node we're deleting.
    */
   void klist_del(struct klist_node *n)
   {
           klist_put(n, true);
   }
   EXPORT_SYMBOL_GPL(klist_del);
   
   /**
    * klist_remove - Decrement the refcount of node and wait for it to go away.
    * @n: node we're removing.
    */
   void klist_remove(struct klist_node *n)
   {
           struct klist_waiter waiter;
   
           waiter.node = n;
           waiter.process = current;
           waiter.woken = 0;
           spin_lock(&klist_remove_lock);
           list_add(&waiter.list, &klist_remove_waiters);
           spin_unlock(&klist_remove_lock);
   
           klist_del(n);
   
           for (;;) {
                   set_current_state(TASK_UNINTERRUPTIBLE);
                   if (waiter.woken)
                           break;
                   schedule();
           }
           __set_current_state(TASK_RUNNING);
   }
   EXPORT_SYMBOL_GPL(klist_remove);
   
   /**
    * klist_node_attached - Say whether a node is bound to a list or not.
    * @n: Node that we're testing.
    */
   int klist_node_attached(struct klist_node *n)
   {
           return (n->n_klist != NULL);
   }
   EXPORT_SYMBOL_GPL(klist_node_attached);
   
   /**
    * klist_iter_init_node - Initialize a klist_iter structure.
    * @k: klist we're iterating.
    * @i: klist_iter we're filling.
    * @n: node to start with.
    *
    * Similar to klist_iter_init(), but starts the action off with @n,
    * instead of with the list head.
    */
   void klist_iter_init_node(struct klist *k, struct klist_iter *i,
                             struct klist_node *n)
   {
           i->i_klist = k;
           i->i_cur = n;
           if (n)
                   kref_get(&n->n_ref);
   }
   EXPORT_SYMBOL_GPL(klist_iter_init_node);
   
   /**
    * klist_iter_init - Iniitalize a klist_iter structure.
    * @k: klist we're iterating.
    * @i: klist_iter structure we're filling.
    *
    * Similar to klist_iter_init_node(), but start with the list head.
    */
   void klist_iter_init(struct klist *k, struct klist_iter *i)
   {
           klist_iter_init_node(k, i, NULL);
   }
   EXPORT_SYMBOL_GPL(klist_iter_init);
   
   /**
    * klist_iter_exit - Finish a list iteration.
    * @i: Iterator structure.
    *
    * Must be called when done iterating over list, as it decrements the
    * refcount of the current node. Necessary in case iteration exited before
    * the end of the list was reached, and always good form.
    */
   void klist_iter_exit(struct klist_iter *i)
   {
           if (i->i_cur) {
                   klist_put(i->i_cur, false);
                   i->i_cur = NULL;
           }
   }
   EXPORT_SYMBOL_GPL(klist_iter_exit);
   
   static struct klist_node *to_klist_node(struct list_head *n)
   {
           return container_of(n, struct klist_node, n_node);
   }
   
   /**
    * klist_next - Ante up next node in list.
    * @i: Iterator structure.
    *
    * First grab list lock. Decrement the reference count of the previous
    * node, if there was one. Grab the next node, increment its reference
    * count, drop the lock, and return that next node.
    */
   struct klist_node *klist_next(struct klist_iter *i)
   {
           void (*put)(struct klist_node *) = i->i_klist->put;
           struct klist_node *last = i->i_cur;
           struct klist_node *next;
   
           spin_lock(&i->i_klist->k_lock);
   
           if (last) {
                   next = to_klist_node(last->n_node.next);
                   if (!klist_dec_and_del(last))
                           put = NULL;
           } else
                   next = to_klist_node(i->i_klist->k_list.next);
   
           i->i_cur = NULL;
           while (next != to_klist_node(&i->i_klist->k_list)) {
                   if (likely(!knode_dead(next))) {
                           kref_get(&next->n_ref);
                           i->i_cur = next;
                           break;
                   }
                   next = to_klist_node(next->n_node.next);
           }
   
           spin_unlock(&i->i_klist->k_lock);
   
           if (put && last)
                   put(last);
           return i->i_cur;
   }
   EXPORT_SYMBOL_GPL(klist_next);

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