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Linux/lib/klist.c

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  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/export.h>
 39 #include <linux/sched.h>
 40 
 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 }
 72 
 73 /**
 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)
 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.
 84  */
 85 void klist_init(struct klist *k, void (*get)(struct klist_node *),
 86                 void (*put)(struct klist_node *))
 87 {
 88         INIT_LIST_HEAD(&k->k_list);
 89         spin_lock_init(&k->k_lock);
 90         k->get = get;
 91         k->put = put;
 92 }
 93 EXPORT_SYMBOL_GPL(klist_init);
 94 
 95 static void add_head(struct klist *k, struct klist_node *n)
 96 {
 97         spin_lock(&k->k_lock);
 98         list_add(&n->n_node, &k->k_list);
 99         spin_unlock(&k->k_lock);
100 }
101 
102 static void add_tail(struct klist *k, struct klist_node *n)
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 
109 static void klist_node_init(struct klist *k, struct klist_node *n)
110 {
111         INIT_LIST_HEAD(&n->n_node);
112         kref_init(&n->n_ref);
113         knode_set_klist(n, k);
114         if (k->get)
115                 k->get(n);
116 }
117 
118 /**
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.
122  */
123 void klist_add_head(struct klist_node *n, struct klist *k)
124 {
125         klist_node_init(k, n);
126         add_head(k, n);
127 }
128 EXPORT_SYMBOL_GPL(klist_add_head);
129 
130 /**
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.
134  */
135 void klist_add_tail(struct klist_node *n, struct klist *k)
136 {
137         klist_node_init(k, n);
138         add_tail(k, n);
139 }
140 EXPORT_SYMBOL_GPL(klist_add_tail);
141 
142 /**
143  * klist_add_behind - 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_behind(struct klist_node *n, struct klist_node *pos)
148 {
149         struct klist *k = knode_klist(pos);
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_behind);
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 {
165         struct klist *k = knode_klist(pos);
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 
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 
184 static void klist_release(struct kref *kref)
185 {
186         struct klist_waiter *waiter, *tmp;
187         struct klist_node *n = container_of(kref, struct klist_node, n_ref);
188 
189         WARN_ON(!knode_dead(n));
190         list_del(&n->n_node);
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                 list_del(&waiter->list);
197                 waiter->woken = 1;
198                 mb();
199                 wake_up_process(waiter->process);
200         }
201         spin_unlock(&klist_remove_lock);
202         knode_set_klist(n, NULL);
203 }
204 
205 static int klist_dec_and_del(struct klist_node *n)
206 {
207         return kref_put(&n->n_ref, klist_release);
208 }
209 
210 static void klist_put(struct klist_node *n, bool kill)
211 {
212         struct klist *k = knode_klist(n);
213         void (*put)(struct klist_node *) = k->put;
214 
215         spin_lock(&k->k_lock);
216         if (kill)
217                 knode_kill(n);
218         if (!klist_dec_and_del(n))
219                 put = NULL;
220         spin_unlock(&k->k_lock);
221         if (put)
222                 put(n);
223 }
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 }
233 EXPORT_SYMBOL_GPL(klist_del);
234 
235 /**
236  * klist_remove - Decrement the refcount of node and wait for it to go away.
237  * @n: node we're removing.
238  */
239 void klist_remove(struct klist_node *n)
240 {
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 
250         klist_del(n);
251 
252         for (;;) {
253                 set_current_state(TASK_UNINTERRUPTIBLE);
254                 if (waiter.woken)
255                         break;
256                 schedule();
257         }
258         __set_current_state(TASK_RUNNING);
259 }
260 EXPORT_SYMBOL_GPL(klist_remove);
261 
262 /**
263  * klist_node_attached - Say whether a node is bound to a list or not.
264  * @n: Node that we're testing.
265  */
266 int klist_node_attached(struct klist_node *n)
267 {
268         return (n->n_klist != NULL);
269 }
270 EXPORT_SYMBOL_GPL(klist_node_attached);
271 
272 /**
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.
277  *
278  * Similar to klist_iter_init(), but starts the action off with @n,
279  * instead of with the list head.
280  */
281 void klist_iter_init_node(struct klist *k, struct klist_iter *i,
282                           struct klist_node *n)
283 {
284         i->i_klist = k;
285         i->i_cur = NULL;
286         if (n && kref_get_unless_zero(&n->n_ref))
287                 i->i_cur = n;
288 }
289 EXPORT_SYMBOL_GPL(klist_iter_init_node);
290 
291 /**
292  * klist_iter_init - Iniitalize a klist_iter structure.
293  * @k: klist we're iterating.
294  * @i: klist_iter structure we're filling.
295  *
296  * Similar to klist_iter_init_node(), but start with the list head.
297  */
298 void klist_iter_init(struct klist *k, struct klist_iter *i)
299 {
300         klist_iter_init_node(k, i, NULL);
301 }
302 EXPORT_SYMBOL_GPL(klist_iter_init);
303 
304 /**
305  * klist_iter_exit - Finish a list iteration.
306  * @i: Iterator structure.
307  *
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.
311  */
312 void klist_iter_exit(struct klist_iter *i)
313 {
314         if (i->i_cur) {
315                 klist_put(i->i_cur, false);
316                 i->i_cur = NULL;
317         }
318 }
319 EXPORT_SYMBOL_GPL(klist_iter_exit);
320 
321 static struct klist_node *to_klist_node(struct list_head *n)
322 {
323         return container_of(n, struct klist_node, n_node);
324 }
325 
326 /**
327  * klist_prev - Ante up prev node in list.
328  * @i: Iterator structure.
329  *
330  * First grab list lock. Decrement the reference count of the previous
331  * node, if there was one. Grab the prev node, increment its reference
332  * count, drop the lock, and return that prev node.
333  */
334 struct klist_node *klist_prev(struct klist_iter *i)
335 {
336         void (*put)(struct klist_node *) = i->i_klist->put;
337         struct klist_node *last = i->i_cur;
338         struct klist_node *prev;
339         unsigned long flags;
340 
341         spin_lock_irqsave(&i->i_klist->k_lock, flags);
342 
343         if (last) {
344                 prev = to_klist_node(last->n_node.prev);
345                 if (!klist_dec_and_del(last))
346                         put = NULL;
347         } else
348                 prev = to_klist_node(i->i_klist->k_list.prev);
349 
350         i->i_cur = NULL;
351         while (prev != to_klist_node(&i->i_klist->k_list)) {
352                 if (likely(!knode_dead(prev))) {
353                         kref_get(&prev->n_ref);
354                         i->i_cur = prev;
355                         break;
356                 }
357                 prev = to_klist_node(prev->n_node.prev);
358         }
359 
360         spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
361 
362         if (put && last)
363                 put(last);
364         return i->i_cur;
365 }
366 EXPORT_SYMBOL_GPL(klist_prev);
367 
368 /**
369  * klist_next - Ante up next node in list.
370  * @i: Iterator structure.
371  *
372  * First grab list lock. Decrement the reference count of the previous
373  * node, if there was one. Grab the next node, increment its reference
374  * count, drop the lock, and return that next node.
375  */
376 struct klist_node *klist_next(struct klist_iter *i)
377 {
378         void (*put)(struct klist_node *) = i->i_klist->put;
379         struct klist_node *last = i->i_cur;
380         struct klist_node *next;
381         unsigned long flags;
382 
383         spin_lock_irqsave(&i->i_klist->k_lock, flags);
384 
385         if (last) {
386                 next = to_klist_node(last->n_node.next);
387                 if (!klist_dec_and_del(last))
388                         put = NULL;
389         } else
390                 next = to_klist_node(i->i_klist->k_list.next);
391 
392         i->i_cur = NULL;
393         while (next != to_klist_node(&i->i_klist->k_list)) {
394                 if (likely(!knode_dead(next))) {
395                         kref_get(&next->n_ref);
396                         i->i_cur = next;
397                         break;
398                 }
399                 next = to_klist_node(next->n_node.next);
400         }
401 
402         spin_unlock_irqrestore(&i->i_klist->k_lock, flags);
403 
404         if (put && last)
405                 put(last);
406         return i->i_cur;
407 }
408 EXPORT_SYMBOL_GPL(klist_next);
409 

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