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
55 void 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
64 EXPORT_SYMBOL_GPL(klist_init);
65
66
67 static 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
74 static 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
82 static 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
99 void klist_add_head(struct klist_node * n, struct klist * k)
100 {
101 klist_node_init(k, n);
102 add_head(k, n);
103 }
104
105 EXPORT_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
114 void klist_add_tail(struct klist_node * n, struct klist * k)
115 {
116 klist_node_init(k, n);
117 add_tail(k, n);
118 }
119
120 EXPORT_SYMBOL_GPL(klist_add_tail);
121
122
123 static 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
132 static 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
143 void 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
156 EXPORT_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
164 void klist_remove(struct klist_node * n)
165 {
166 klist_del(n);
167 wait_for_completion(&n->n_removed);
168 }
169
170 EXPORT_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
178 int klist_node_attached(struct klist_node * n)
179 {
180 return (n->n_klist != NULL);
181 }
182
183 EXPORT_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
196 void 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
205 EXPORT_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
216 void klist_iter_init(struct klist * k, struct klist_iter * i)
217 {
218 klist_iter_init_node(k, i, NULL);
219 }
220
221 EXPORT_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
233 void 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
241 EXPORT_SYMBOL_GPL(klist_iter_exit);
242
243
244 static 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
259 struct 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
285 EXPORT_SYMBOL_GPL(klist_next);
286
287
288
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