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9a19fea [PATCH] Add initial implementation of klist helpers.
mochel@digitalimplant.org authored
1 /*
c3bb7fa @gregkh klist: fix coding style errors in klist.h and klist.c
gregkh authored
2 * klist.c - Routines for manipulating klists.
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3 *
c3bb7fa @gregkh klist: fix coding style errors in klist.h and klist.c
gregkh authored
4 * Copyright (C) 2005 Patrick Mochel
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5 *
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gregkh authored
6 * This file is released under the GPL v2.
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7 *
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gregkh authored
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.
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15 *
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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.
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20 *
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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.
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27 *
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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).
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35 */
36
37 #include <linux/klist.h>
38 #include <linux/module.h>
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39 #include <linux/sched.h>
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40
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41 /*
42 * Use the lowest bit of n_klist to mark deleted nodes and exclude
43 * dead ones from iteration.
44 */
45 #define KNODE_DEAD 1LU
46 #define KNODE_KLIST_MASK ~KNODE_DEAD
47
48 static struct klist *knode_klist(struct klist_node *knode)
49 {
50 return (struct klist *)
51 ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
52 }
53
54 static bool knode_dead(struct klist_node *knode)
55 {
56 return (unsigned long)knode->n_klist & KNODE_DEAD;
57 }
58
59 static void knode_set_klist(struct klist_node *knode, struct klist *klist)
60 {
61 knode->n_klist = klist;
62 /* no knode deserves to start its life dead */
63 WARN_ON(knode_dead(knode));
64 }
65
66 static void knode_kill(struct klist_node *knode)
67 {
68 /* and no knode should die twice ever either, see we're very humane */
69 WARN_ON(knode_dead(knode));
70 *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
71 }
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72
73 /**
c3bb7fa @gregkh klist: fix coding style errors in klist.h and klist.c
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74 * klist_init - Initialize a klist structure.
75 * @k: The klist we're initializing.
76 * @get: The get function for the embedding object (NULL if none)
77 * @put: The put function for the embedding object (NULL if none)
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78 *
79 * Initialises the klist structure. If the klist_node structures are
80 * going to be embedded in refcounted objects (necessary for safe
81 * deletion) then the get/put arguments are used to initialise
82 * functions that take and release references on the embedding
83 * objects.
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84 */
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85 void klist_init(struct klist *k, void (*get)(struct klist_node *),
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86 void (*put)(struct klist_node *))
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87 {
88 INIT_LIST_HEAD(&k->k_list);
89 spin_lock_init(&k->k_lock);
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90 k->get = get;
91 k->put = put;
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92 }
93 EXPORT_SYMBOL_GPL(klist_init);
94
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95 static void add_head(struct klist *k, struct klist_node *n)
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96 {
97 spin_lock(&k->k_lock);
98 list_add(&n->n_node, &k->k_list);
99 spin_unlock(&k->k_lock);
100 }
101
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102 static void add_tail(struct klist *k, struct klist_node *n)
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103 {
104 spin_lock(&k->k_lock);
105 list_add_tail(&n->n_node, &k->k_list);
106 spin_unlock(&k->k_lock);
107 }
108
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109 static void klist_node_init(struct klist *k, struct klist_node *n)
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110 {
111 INIT_LIST_HEAD(&n->n_node);
112 kref_init(&n->n_ref);
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113 knode_set_klist(n, k);
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114 if (k->get)
115 k->get(n);
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116 }
117
118 /**
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119 * klist_add_head - Initialize a klist_node and add it to front.
120 * @n: node we're adding.
121 * @k: klist it's going on.
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122 */
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123 void klist_add_head(struct klist_node *n, struct klist *k)
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124 {
125 klist_node_init(k, n);
126 add_head(k, n);
127 }
128 EXPORT_SYMBOL_GPL(klist_add_head);
129
130 /**
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131 * klist_add_tail - Initialize a klist_node and add it to back.
132 * @n: node we're adding.
133 * @k: klist it's going on.
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134 */
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135 void klist_add_tail(struct klist_node *n, struct klist *k)
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136 {
137 klist_node_init(k, n);
138 add_tail(k, n);
139 }
140 EXPORT_SYMBOL_GPL(klist_add_tail);
141
93dd400 @htejun klist: implement klist_add_{after|before}()
htejun authored
142 /**
143 * klist_add_after - Init a klist_node and add it after an existing node
144 * @n: node we're adding.
145 * @pos: node to put @n after
146 */
147 void klist_add_after(struct klist_node *n, struct klist_node *pos)
148 {
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149 struct klist *k = knode_klist(pos);
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150
151 klist_node_init(k, n);
152 spin_lock(&k->k_lock);
153 list_add(&n->n_node, &pos->n_node);
154 spin_unlock(&k->k_lock);
155 }
156 EXPORT_SYMBOL_GPL(klist_add_after);
157
158 /**
159 * klist_add_before - Init a klist_node and add it before an existing node
160 * @n: node we're adding.
161 * @pos: node to put @n after
162 */
163 void klist_add_before(struct klist_node *n, struct klist_node *pos)
164 {
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165 struct klist *k = knode_klist(pos);
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166
167 klist_node_init(k, n);
168 spin_lock(&k->k_lock);
169 list_add_tail(&n->n_node, &pos->n_node);
170 spin_unlock(&k->k_lock);
171 }
172 EXPORT_SYMBOL_GPL(klist_add_before);
173
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174 struct klist_waiter {
175 struct list_head list;
176 struct klist_node *node;
177 struct task_struct *process;
178 int woken;
179 };
180
181 static DEFINE_SPINLOCK(klist_remove_lock);
182 static LIST_HEAD(klist_remove_waiters);
183
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184 static void klist_release(struct kref *kref)
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185 {
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186 struct klist_waiter *waiter, *tmp;
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187 struct klist_node *n = container_of(kref, struct klist_node, n_ref);
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188
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189 WARN_ON(!knode_dead(n));
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190 list_del(&n->n_node);
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191 spin_lock(&klist_remove_lock);
192 list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
193 if (waiter->node != n)
194 continue;
195
196 waiter->woken = 1;
197 mb();
198 wake_up_process(waiter->process);
199 list_del(&waiter->list);
200 }
201 spin_unlock(&klist_remove_lock);
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202 knode_set_klist(n, NULL);
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203 }
204
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205 static int klist_dec_and_del(struct klist_node *n)
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206 {
207 return kref_put(&n->n_ref, klist_release);
208 }
209
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210 static void klist_put(struct klist_node *n, bool kill)
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211 {
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212 struct klist *k = knode_klist(n);
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213 void (*put)(struct klist_node *) = k->put;
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214
215 spin_lock(&k->k_lock);
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216 if (kill)
217 knode_kill(n);
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218 if (!klist_dec_and_del(n))
219 put = NULL;
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220 spin_unlock(&k->k_lock);
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221 if (put)
222 put(n);
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223 }
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224
225 /**
226 * klist_del - Decrement the reference count of node and try to remove.
227 * @n: node we're deleting.
228 */
229 void klist_del(struct klist_node *n)
230 {
231 klist_put(n, true);
232 }
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233 EXPORT_SYMBOL_GPL(klist_del);
234
235 /**
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236 * klist_remove - Decrement the refcount of node and wait for it to go away.
237 * @n: node we're removing.
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238 */
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239 void klist_remove(struct klist_node *n)
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240 {
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241 struct klist_waiter waiter;
242
243 waiter.node = n;
244 waiter.process = current;
245 waiter.woken = 0;
246 spin_lock(&klist_remove_lock);
247 list_add(&waiter.list, &klist_remove_waiters);
248 spin_unlock(&klist_remove_lock);
249
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250 klist_del(n);
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251
252 for (;;) {
253 set_current_state(TASK_UNINTERRUPTIBLE);
254 if (waiter.woken)
255 break;
256 schedule();
257 }
258 __set_current_state(TASK_RUNNING);
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259 }
260 EXPORT_SYMBOL_GPL(klist_remove);
261
262 /**
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263 * klist_node_attached - Say whether a node is bound to a list or not.
264 * @n: Node that we're testing.
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265 */
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266 int klist_node_attached(struct klist_node *n)
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267 {
268 return (n->n_klist != NULL);
269 }
270 EXPORT_SYMBOL_GPL(klist_node_attached);
271
272 /**
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273 * klist_iter_init_node - Initialize a klist_iter structure.
274 * @k: klist we're iterating.
275 * @i: klist_iter we're filling.
276 * @n: node to start with.
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277 *
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278 * Similar to klist_iter_init(), but starts the action off with @n,
279 * instead of with the list head.
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280 */
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281 void klist_iter_init_node(struct klist *k, struct klist_iter *i,
282 struct klist_node *n)
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283 {
284 i->i_klist = k;
285 i->i_cur = n;
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286 if (n)
287 kref_get(&n->n_ref);
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288 }
289 EXPORT_SYMBOL_GPL(klist_iter_init_node);
290
291 /**
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292 * klist_iter_init - Iniitalize a klist_iter structure.
293 * @k: klist we're iterating.
294 * @i: klist_iter structure we're filling.
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295 *
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296 * Similar to klist_iter_init_node(), but start with the list head.
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297 */
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298 void klist_iter_init(struct klist *k, struct klist_iter *i)
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299 {
300 klist_iter_init_node(k, i, NULL);
301 }
302 EXPORT_SYMBOL_GPL(klist_iter_init);
303
304 /**
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305 * klist_iter_exit - Finish a list iteration.
306 * @i: Iterator structure.
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307 *
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308 * Must be called when done iterating over list, as it decrements the
309 * refcount of the current node. Necessary in case iteration exited before
310 * the end of the list was reached, and always good form.
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311 */
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312 void klist_iter_exit(struct klist_iter *i)
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313 {
314 if (i->i_cur) {
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315 klist_put(i->i_cur, false);
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316 i->i_cur = NULL;
317 }
318 }
319 EXPORT_SYMBOL_GPL(klist_iter_exit);
320
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321 static struct klist_node *to_klist_node(struct list_head *n)
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322 {
323 return container_of(n, struct klist_node, n_node);
324 }
325
326 /**
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327 * klist_next - Ante up next node in list.
328 * @i: Iterator structure.
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329 *
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330 * First grab list lock. Decrement the reference count of the previous
331 * node, if there was one. Grab the next node, increment its reference
332 * count, drop the lock, and return that next node.
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333 */
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334 struct klist_node *klist_next(struct klist_iter *i)
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335 {
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336 void (*put)(struct klist_node *) = i->i_klist->put;
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337 struct klist_node *last = i->i_cur;
338 struct klist_node *next;
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339
340 spin_lock(&i->i_klist->k_lock);
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341
342 if (last) {
343 next = to_klist_node(last->n_node.next);
344 if (!klist_dec_and_del(last))
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345 put = NULL;
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346 } else
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347 next = to_klist_node(i->i_klist->k_list.next);
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348
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349 i->i_cur = NULL;
350 while (next != to_klist_node(&i->i_klist->k_list)) {
351 if (likely(!knode_dead(next))) {
352 kref_get(&next->n_ref);
353 i->i_cur = next;
354 break;
355 }
356 next = to_klist_node(next->n_node.next);
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357 }
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358
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359 spin_unlock(&i->i_klist->k_lock);
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360
361 if (put && last)
362 put(last);
363 return i->i_cur;
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364 }
365 EXPORT_SYMBOL_GPL(klist_next);
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