xref: /openbmc/linux/lib/klist.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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