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