/* * klist.c - Routines for manipulating klists. * * * 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). * * Copyright (C) 2005 Patrick Mochel * * This file is released under the GPL v2. */ #include <linux/klist.h> #include <linux/module.h> /** * klist_init - Initialize a klist structure. * @k: The klist we're initializing. */ void klist_init(struct klist * k) { INIT_LIST_HEAD(&k->k_list); spin_lock_init(&k->k_lock); } 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); init_completion(&n->n_removed); kref_init(&n->n_ref); n->n_klist = k; } /** * klist_add_head - Initialize a klist_node and add it to front. * @k: klist it's going on. * @n: node we're adding. */ void klist_add_head(struct klist * k, struct klist_node * n) { 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. * @k: klist it's going on. * @n: node we're adding. */ void klist_add_tail(struct klist * k, struct klist_node * n) { klist_node_init(k, n); add_tail(k, n); } EXPORT_SYMBOL_GPL(klist_add_tail); static void klist_release(struct kref * kref) { struct klist_node * n = container_of(kref, struct klist_node, n_ref); list_del(&n->n_node); complete(&n->n_removed); n->n_klist = NULL; } static int klist_dec_and_del(struct klist_node * n) { return kref_put(&n->n_ref, klist_release); } /** * klist_del - Decrement the reference count of node and try to remove. * @n: node we're deleting. */ void klist_del(struct klist_node * n) { struct klist * k = n->n_klist; spin_lock(&k->k_lock); klist_dec_and_del(n); spin_unlock(&k->k_lock); } 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 * k = n->n_klist; spin_lock(&k->k_lock); klist_dec_and_del(n); spin_unlock(&k->k_lock); wait_for_completion(&n->n_removed); } 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_head = &k->k_list; i->i_cur = n; } 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_del(i->i_cur); 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) { struct list_head * next; struct klist_node * knode = NULL; spin_lock(&i->i_klist->k_lock); if (i->i_cur) { next = i->i_cur->n_node.next; klist_dec_and_del(i->i_cur); } else next = i->i_head->next; if (next != i->i_head) { knode = to_klist_node(next); kref_get(&knode->n_ref); } i->i_cur = knode; spin_unlock(&i->i_klist->k_lock); return knode; } EXPORT_SYMBOL_GPL(klist_next);