/* * 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; 		list_del(&waiter->list);		waiter->woken = 1;		mb();		wake_up_process(waiter->process);	}	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);