Root/lib/klist.c

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#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
48static struct klist *knode_klist(struct klist_node *knode)
49{
50    return (struct klist *)
51        ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
52}
53
54static bool knode_dead(struct klist_node *knode)
55{
56    return (unsigned long)knode->n_klist & KNODE_DEAD;
57}
58
59static 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
66static 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 */
85void 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}
93EXPORT_SYMBOL_GPL(klist_init);
94
95static 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
102static 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
109static 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 */
123void klist_add_head(struct klist_node *n, struct klist *k)
124{
125    klist_node_init(k, n);
126    add_head(k, n);
127}
128EXPORT_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 */
135void klist_add_tail(struct klist_node *n, struct klist *k)
136{
137    klist_node_init(k, n);
138    add_tail(k, n);
139}
140EXPORT_SYMBOL_GPL(klist_add_tail);
141
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 */
147void klist_add_after(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}
156EXPORT_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 */
163void 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}
172EXPORT_SYMBOL_GPL(klist_add_before);
173
174struct klist_waiter {
175    struct list_head list;
176    struct klist_node *node;
177    struct task_struct *process;
178    int woken;
179};
180
181static DEFINE_SPINLOCK(klist_remove_lock);
182static LIST_HEAD(klist_remove_waiters);
183
184static 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        waiter->woken = 1;
197        mb();
198        wake_up_process(waiter->process);
199        list_del(&waiter->list);
200    }
201    spin_unlock(&klist_remove_lock);
202    knode_set_klist(n, NULL);
203}
204
205static int klist_dec_and_del(struct klist_node *n)
206{
207    return kref_put(&n->n_ref, klist_release);
208}
209
210static 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 */
229void klist_del(struct klist_node *n)
230{
231    klist_put(n, true);
232}
233EXPORT_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 */
239void 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}
260EXPORT_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 */
266int klist_node_attached(struct klist_node *n)
267{
268    return (n->n_klist != NULL);
269}
270EXPORT_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 */
281void 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 = n;
286    if (n)
287        kref_get(&n->n_ref);
288}
289EXPORT_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 */
298void klist_iter_init(struct klist *k, struct klist_iter *i)
299{
300    klist_iter_init_node(k, i, NULL);
301}
302EXPORT_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 */
312void 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}
319EXPORT_SYMBOL_GPL(klist_iter_exit);
320
321static 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_next - Ante up next 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 next node, increment its reference
332 * count, drop the lock, and return that next node.
333 */
334struct klist_node *klist_next(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 *next;
339
340    spin_lock(&i->i_klist->k_lock);
341
342    if (last) {
343        next = to_klist_node(last->n_node.next);
344        if (!klist_dec_and_del(last))
345            put = NULL;
346    } else
347        next = to_klist_node(i->i_klist->k_list.next);
348
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);
357    }
358
359    spin_unlock(&i->i_klist->k_lock);
360
361    if (put && last)
362        put(last);
363    return i->i_cur;
364}
365EXPORT_SYMBOL_GPL(klist_next);
366

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