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linux
1/*
2 * klist.c - Routines for manipulating klists.
3 *
4 * Copyright (C) 2005 Patrick Mochel
5 *
6 * This file is released under the GPL v2.
7 *
8 * This klist interface provides a couple of structures that wrap around
9 * struct list_head to provide explicit list "head" (struct klist) and list
10 * "node" (struct klist_node) objects. For struct klist, a spinlock is
11 * included that protects access to the actual list itself. struct
12 * klist_node provides a pointer to the klist that owns it and a kref
13 * reference count that indicates the number of current users of that node
14 * in the list.
15 *
16 * The entire point is to provide an interface for iterating over a list
17 * that is safe and allows for modification of the list during the
18 * iteration (e.g. insertion and removal), including modification of the
19 * current node on the list.
20 *
21 * It works using a 3rd object type - struct klist_iter - that is declared
22 * and initialized before an iteration. klist_next() is used to acquire the
23 * next element in the list. It returns NULL if there are no more items.
24 * Internally, that routine takes the klist's lock, decrements the
25 * reference count of the previous klist_node and increments the count of
26 * the next klist_node. It then drops the lock and returns.
27 *
28 * There are primitives for adding and removing nodes to/from a klist.
29 * When deleting, klist_del() will simply decrement the reference count.
30 * Only when the count goes to 0 is the node removed from the list.
31 * klist_remove() will try to delete the node from the list and block until
32 * it is actually removed. This is useful for objects (like devices) that
33 * have been removed from the system and must be freed (but must wait until
34 * all accessors have finished).
35 */
36
37#include <linux/klist.h>
38#include <linux/module.h>
39
40
41/**
42 * klist_init - Initialize a klist structure.
43 * @k: The klist we're initializing.
44 * @get: The get function for the embedding object (NULL if none)
45 * @put: The put function for the embedding object (NULL if none)
46 *
47 * Initialises the klist structure. If the klist_node structures are
48 * going to be embedded in refcounted objects (necessary for safe
49 * deletion) then the get/put arguments are used to initialise
50 * functions that take and release references on the embedding
51 * objects.
52 */
53void klist_init(struct klist *k, void (*get)(struct klist_node *),
54 void (*put)(struct klist_node *))
55{
56 INIT_LIST_HEAD(&k->k_list);
57 spin_lock_init(&k->k_lock);
58 k->get = get;
59 k->put = put;
60}
61EXPORT_SYMBOL_GPL(klist_init);
62
63static void add_head(struct klist *k, struct klist_node *n)
64{
65 spin_lock(&k->k_lock);
66 list_add(&n->n_node, &k->k_list);
67 spin_unlock(&k->k_lock);
68}
69
70static void add_tail(struct klist *k, struct klist_node *n)
71{
72 spin_lock(&k->k_lock);
73 list_add_tail(&n->n_node, &k->k_list);
74 spin_unlock(&k->k_lock);
75}
76
77static void klist_node_init(struct klist *k, struct klist_node *n)
78{
79 INIT_LIST_HEAD(&n->n_node);
80 init_completion(&n->n_removed);
81 kref_init(&n->n_ref);
82 n->n_klist = k;
83 if (k->get)
84 k->get(n);
85}
86
87/**
88 * klist_add_head - Initialize a klist_node and add it to front.
89 * @n: node we're adding.
90 * @k: klist it's going on.
91 */
92void klist_add_head(struct klist_node *n, struct klist *k)
93{
94 klist_node_init(k, n);
95 add_head(k, n);
96}
97EXPORT_SYMBOL_GPL(klist_add_head);
98
99/**
100 * klist_add_tail - Initialize a klist_node and add it to back.
101 * @n: node we're adding.
102 * @k: klist it's going on.
103 */
104void klist_add_tail(struct klist_node *n, struct klist *k)
105{
106 klist_node_init(k, n);
107 add_tail(k, n);
108}
109EXPORT_SYMBOL_GPL(klist_add_tail);
110
111/**
112 * klist_add_after - Init a klist_node and add it after an existing node
113 * @n: node we're adding.
114 * @pos: node to put @n after
115 */
116void klist_add_after(struct klist_node *n, struct klist_node *pos)
117{
118 struct klist *k = pos->n_klist;
119
120 klist_node_init(k, n);
121 spin_lock(&k->k_lock);
122 list_add(&n->n_node, &pos->n_node);
123 spin_unlock(&k->k_lock);
124}
125EXPORT_SYMBOL_GPL(klist_add_after);
126
127/**
128 * klist_add_before - Init a klist_node and add it before an existing node
129 * @n: node we're adding.
130 * @pos: node to put @n after
131 */
132void klist_add_before(struct klist_node *n, struct klist_node *pos)
133{
134 struct klist *k = pos->n_klist;
135
136 klist_node_init(k, n);
137 spin_lock(&k->k_lock);
138 list_add_tail(&n->n_node, &pos->n_node);
139 spin_unlock(&k->k_lock);
140}
141EXPORT_SYMBOL_GPL(klist_add_before);
142
143static void klist_release(struct kref *kref)
144{
145 struct klist_node *n = container_of(kref, struct klist_node, n_ref);
146
147 list_del(&n->n_node);
148 complete(&n->n_removed);
149 n->n_klist = NULL;
150}
151
152static int klist_dec_and_del(struct klist_node *n)
153{
154 return kref_put(&n->n_ref, klist_release);
155}
156
157/**
158 * klist_del - Decrement the reference count of node and try to remove.
159 * @n: node we're deleting.
160 */
161void klist_del(struct klist_node *n)
162{
163 struct klist *k = n->n_klist;
164 void (*put)(struct klist_node *) = k->put;
165
166 spin_lock(&k->k_lock);
167 if (!klist_dec_and_del(n))
168 put = NULL;
169 spin_unlock(&k->k_lock);
170 if (put)
171 put(n);
172}
173EXPORT_SYMBOL_GPL(klist_del);
174
175/**
176 * klist_remove - Decrement the refcount of node and wait for it to go away.
177 * @n: node we're removing.
178 */
179void klist_remove(struct klist_node *n)
180{
181 klist_del(n);
182 wait_for_completion(&n->n_removed);
183}
184EXPORT_SYMBOL_GPL(klist_remove);
185
186/**
187 * klist_node_attached - Say whether a node is bound to a list or not.
188 * @n: Node that we're testing.
189 */
190int klist_node_attached(struct klist_node *n)
191{
192 return (n->n_klist != NULL);
193}
194EXPORT_SYMBOL_GPL(klist_node_attached);
195
196/**
197 * klist_iter_init_node - Initialize a klist_iter structure.
198 * @k: klist we're iterating.
199 * @i: klist_iter we're filling.
200 * @n: node to start with.
201 *
202 * Similar to klist_iter_init(), but starts the action off with @n,
203 * instead of with the list head.
204 */
205void klist_iter_init_node(struct klist *k, struct klist_iter *i,
206 struct klist_node *n)
207{
208 i->i_klist = k;
209 i->i_head = &k->k_list;
210 i->i_cur = n;
211 if (n)
212 kref_get(&n->n_ref);
213}
214EXPORT_SYMBOL_GPL(klist_iter_init_node);
215
216/**
217 * klist_iter_init - Iniitalize a klist_iter structure.
218 * @k: klist we're iterating.
219 * @i: klist_iter structure we're filling.
220 *
221 * Similar to klist_iter_init_node(), but start with the list head.
222 */
223void klist_iter_init(struct klist *k, struct klist_iter *i)
224{
225 klist_iter_init_node(k, i, NULL);
226}
227EXPORT_SYMBOL_GPL(klist_iter_init);
228
229/**
230 * klist_iter_exit - Finish a list iteration.
231 * @i: Iterator structure.
232 *
233 * Must be called when done iterating over list, as it decrements the
234 * refcount of the current node. Necessary in case iteration exited before
235 * the end of the list was reached, and always good form.
236 */
237void klist_iter_exit(struct klist_iter *i)
238{
239 if (i->i_cur) {
240 klist_del(i->i_cur);
241 i->i_cur = NULL;
242 }
243}
244EXPORT_SYMBOL_GPL(klist_iter_exit);
245
246static struct klist_node *to_klist_node(struct list_head *n)
247{
248 return container_of(n, struct klist_node, n_node);
249}
250
251/**
252 * klist_next - Ante up next node in list.
253 * @i: Iterator structure.
254 *
255 * First grab list lock. Decrement the reference count of the previous
256 * node, if there was one. Grab the next node, increment its reference
257 * count, drop the lock, and return that next node.
258 */
259struct klist_node *klist_next(struct klist_iter *i)
260{
261 struct list_head *next;
262 struct klist_node *lnode = i->i_cur;
263 struct klist_node *knode = NULL;
264 void (*put)(struct klist_node *) = i->i_klist->put;
265
266 spin_lock(&i->i_klist->k_lock);
267 if (lnode) {
268 next = lnode->n_node.next;
269 if (!klist_dec_and_del(lnode))
270 put = NULL;
271 } else
272 next = i->i_head->next;
273
274 if (next != i->i_head) {
275 knode = to_klist_node(next);
276 kref_get(&knode->n_ref);
277 }
278 i->i_cur = knode;
279 spin_unlock(&i->i_klist->k_lock);
280 if (put && lnode)
281 put(lnode);
282 return knode;
283}
284EXPORT_SYMBOL_GPL(klist_next);