1/*
2 *	klist.c - Routines for manipulating klists.
3 *
4 *
5 *	This klist interface provides a couple of structures that wrap around
6 *	struct list_head to provide explicit list "head" (struct klist) and
7 *	list "node" (struct klist_node) objects. For struct klist, a spinlock
8 *	is included that protects access to the actual list itself. struct
9 *	klist_node provides a pointer to the klist that owns it and a kref
10 *	reference count that indicates the number of current users of that node
11 *	in the list.
12 *
13 *	The entire point is to provide an interface for iterating over a list
14 *	that is safe and allows for modification of the list during the
15 *	iteration (e.g. insertion and removal), including modification of the
16 *	current node on the list.
17 *
18 *	It works using a 3rd object type - struct klist_iter - that is declared
19 *	and initialized before an iteration. klist_next() is used to acquire the
20 *	next element in the list. It returns NULL if there are no more items.
21 *	Internally, that routine takes the klist's lock, decrements the reference
22 *	count of the previous klist_node and increments the count of the next
23 *	klist_node. It then drops the lock and returns.
24 *
25 *	There are primitives for adding and removing nodes to/from a klist.
26 *	When deleting, klist_del() will simply decrement the reference count.
27 *	Only when the count goes to 0 is the node removed from the list.
28 *	klist_remove() will try to delete the node from the list and block
29 *	until it is actually removed. This is useful for objects (like devices)
30 *	that have been removed from the system and must be freed (but must wait
31 *	until all accessors have finished).
32 *
33 *	Copyright (C) 2005 Patrick Mochel
34 *
35 *	This file is released under the GPL v2.
36 */
37
38#include <linux/klist.h>
39#include <linux/module.h>
40
41
42/**
43 *	klist_init - Initialize a klist structure.
44 *	@k:	The klist we're initializing.
45 *	@get:	The get function for the embedding object (NULL if none)
46 *	@put:	The put function for the embedding object (NULL if none)
47 *
48 * Initialises the klist structure.  If the klist_node structures are
49 * going to be embedded in refcounted objects (necessary for safe
50 * deletion) then the get/put arguments are used to initialise
51 * functions that take and release references on the embedding
52 * objects.
53 */
54
55void klist_init(struct klist * k, void (*get)(struct klist_node *),
56		void (*put)(struct klist_node *))
57{
58	INIT_LIST_HEAD(&k->k_list);
59	spin_lock_init(&k->k_lock);
60	k->get = get;
61	k->put = put;
62}
63
64EXPORT_SYMBOL_GPL(klist_init);
65
66
67static void add_head(struct klist * k, struct klist_node * n)
68{
69	spin_lock(&k->k_lock);
70	list_add(&n->n_node, &k->k_list);
71	spin_unlock(&k->k_lock);
72}
73
74static void add_tail(struct klist * k, struct klist_node * n)
75{
76	spin_lock(&k->k_lock);
77	list_add_tail(&n->n_node, &k->k_list);
78	spin_unlock(&k->k_lock);
79}
80
81
82static void klist_node_init(struct klist * k, struct klist_node * n)
83{
84	INIT_LIST_HEAD(&n->n_node);
85	init_completion(&n->n_removed);
86	kref_init(&n->n_ref);
87	n->n_klist = k;
88	if (k->get)
89		k->get(n);
90}
91
92
93/**
94 *	klist_add_head - Initialize a klist_node and add it to front.
95 *	@n:	node we're adding.
96 *	@k:	klist it's going on.
97 */
98
99void klist_add_head(struct klist_node * n, struct klist * k)
100{
101	klist_node_init(k, n);
102	add_head(k, n);
103}
104
105EXPORT_SYMBOL_GPL(klist_add_head);
106
107
108/**
109 *	klist_add_tail - Initialize a klist_node and add it to back.
110 *	@n:	node we're adding.
111 *	@k:	klist it's going on.
112 */
113
114void klist_add_tail(struct klist_node * n, struct klist * k)
115{
116	klist_node_init(k, n);
117	add_tail(k, n);
118}
119
120EXPORT_SYMBOL_GPL(klist_add_tail);
121
122
123static void klist_release(struct kref * kref)
124{
125	struct klist_node * n = container_of(kref, struct klist_node, n_ref);
126
127	list_del(&n->n_node);
128	complete(&n->n_removed);
129	n->n_klist = NULL;
130}
131
132static int klist_dec_and_del(struct klist_node * n)
133{
134	return kref_put(&n->n_ref, klist_release);
135}
136
137
138/**
139 *	klist_del - Decrement the reference count of node and try to remove.
140 *	@n:	node we're deleting.
141 */
142
143void klist_del(struct klist_node * n)
144{
145	struct klist * k = n->n_klist;
146	void (*put)(struct klist_node *) = k->put;
147
148	spin_lock(&k->k_lock);
149	if (!klist_dec_and_del(n))
150		put = NULL;
151	spin_unlock(&k->k_lock);
152	if (put)
153		put(n);
154}
155
156EXPORT_SYMBOL_GPL(klist_del);
157
158
159/**
160 *	klist_remove - Decrement the refcount of node and wait for it to go away.
161 *	@n:	node we're removing.
162 */
163
164void klist_remove(struct klist_node * n)
165{
166	klist_del(n);
167	wait_for_completion(&n->n_removed);
168}
169
170EXPORT_SYMBOL_GPL(klist_remove);
171
172
173/**
174 *	klist_node_attached - Say whether a node is bound to a list or not.
175 *	@n:	Node that we're testing.
176 */
177
178int klist_node_attached(struct klist_node * n)
179{
180	return (n->n_klist != NULL);
181}
182
183EXPORT_SYMBOL_GPL(klist_node_attached);
184
185
186/**
187 *	klist_iter_init_node - Initialize a klist_iter structure.
188 *	@k:	klist we're iterating.
189 *	@i:	klist_iter we're filling.
190 *	@n:	node to start with.
191 *
192 *	Similar to klist_iter_init(), but starts the action off with @n,
193 *	instead of with the list head.
194 */
195
196void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n)
197{
198	i->i_klist = k;
199	i->i_head = &k->k_list;
200	i->i_cur = n;
201	if (n)
202		kref_get(&n->n_ref);
203}
204
205EXPORT_SYMBOL_GPL(klist_iter_init_node);
206
207
208/**
209 *	klist_iter_init - Iniitalize a klist_iter structure.
210 *	@k:	klist we're iterating.
211 *	@i:	klist_iter structure we're filling.
212 *
213 *	Similar to klist_iter_init_node(), but start with the list head.
214 */
215
216void klist_iter_init(struct klist * k, struct klist_iter * i)
217{
218	klist_iter_init_node(k, i, NULL);
219}
220
221EXPORT_SYMBOL_GPL(klist_iter_init);
222
223
224/**
225 *	klist_iter_exit - Finish a list iteration.
226 *	@i:	Iterator structure.
227 *
228 *	Must be called when done iterating over list, as it decrements the
229 *	refcount of the current node. Necessary in case iteration exited before
230 *	the end of the list was reached, and always good form.
231 */
232
233void klist_iter_exit(struct klist_iter * i)
234{
235	if (i->i_cur) {
236		klist_del(i->i_cur);
237		i->i_cur = NULL;
238	}
239}
240
241EXPORT_SYMBOL_GPL(klist_iter_exit);
242
243
244static struct klist_node * to_klist_node(struct list_head * n)
245{
246	return container_of(n, struct klist_node, n_node);
247}
248
249
250/**
251 *	klist_next - Ante up next node in list.
252 *	@i:	Iterator structure.
253 *
254 *	First grab list lock. Decrement the reference count of the previous
255 *	node, if there was one. Grab the next node, increment its reference
256 *	count, drop the lock, and return that next node.
257 */
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}
284
285EXPORT_SYMBOL_GPL(klist_next);
286