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 40 41 /** 42 * klist_init - Initialize a klist structure. 43 * @k: The klist we're initializing. 44 * @get: The get function for the embedding object (NULL if none) 45 * @put: The put function for the embedding object (NULL if none) 46 * 47 * Initialises the klist structure. If the klist_node structures are 48 * going to be embedded in refcounted objects (necessary for safe 49 * deletion) then the get/put arguments are used to initialise 50 * functions that take and release references on the embedding 51 * objects. 52 */ 53 void klist_init(struct klist *k, void (*get)(struct klist_node *), 54 void (*put)(struct klist_node *)) 55 { 56 INIT_LIST_HEAD(&k->k_list); 57 spin_lock_init(&k->k_lock); 58 k->get = get; 59 k->put = put; 60 } 61 EXPORT_SYMBOL_GPL(klist_init); 62 63 static void add_head(struct klist *k, struct klist_node *n) 64 { 65 spin_lock(&k->k_lock); 66 list_add(&n->n_node, &k->k_list); 67 spin_unlock(&k->k_lock); 68 } 69 70 static void add_tail(struct klist *k, struct klist_node *n) 71 { 72 spin_lock(&k->k_lock); 73 list_add_tail(&n->n_node, &k->k_list); 74 spin_unlock(&k->k_lock); 75 } 76 77 static void klist_node_init(struct klist *k, struct klist_node *n) 78 { 79 INIT_LIST_HEAD(&n->n_node); 80 init_completion(&n->n_removed); 81 kref_init(&n->n_ref); 82 n->n_klist = k; 83 if (k->get) 84 k->get(n); 85 } 86 87 /** 88 * klist_add_head - Initialize a klist_node and add it to front. 89 * @n: node we're adding. 90 * @k: klist it's going on. 91 */ 92 void klist_add_head(struct klist_node *n, struct klist *k) 93 { 94 klist_node_init(k, n); 95 add_head(k, n); 96 } 97 EXPORT_SYMBOL_GPL(klist_add_head); 98 99 /** 100 * klist_add_tail - Initialize a klist_node and add it to back. 101 * @n: node we're adding. 102 * @k: klist it's going on. 103 */ 104 void klist_add_tail(struct klist_node *n, struct klist *k) 105 { 106 klist_node_init(k, n); 107 add_tail(k, n); 108 } 109 EXPORT_SYMBOL_GPL(klist_add_tail); 110 111 /** 112 * klist_add_after - Init a klist_node and add it after an existing node 113 * @n: node we're adding. 114 * @pos: node to put @n after 115 */ 116 void klist_add_after(struct klist_node *n, struct klist_node *pos) 117 { 118 struct klist *k = pos->n_klist; 119 120 klist_node_init(k, n); 121 spin_lock(&k->k_lock); 122 list_add(&n->n_node, &pos->n_node); 123 spin_unlock(&k->k_lock); 124 } 125 EXPORT_SYMBOL_GPL(klist_add_after); 126 127 /** 128 * klist_add_before - Init a klist_node and add it before an existing node 129 * @n: node we're adding. 130 * @pos: node to put @n after 131 */ 132 void klist_add_before(struct klist_node *n, struct klist_node *pos) 133 { 134 struct klist *k = pos->n_klist; 135 136 klist_node_init(k, n); 137 spin_lock(&k->k_lock); 138 list_add_tail(&n->n_node, &pos->n_node); 139 spin_unlock(&k->k_lock); 140 } 141 EXPORT_SYMBOL_GPL(klist_add_before); 142 143 static void klist_release(struct kref *kref) 144 { 145 struct klist_node *n = container_of(kref, struct klist_node, n_ref); 146 147 list_del(&n->n_node); 148 complete(&n->n_removed); 149 n->n_klist = NULL; 150 } 151 152 static int klist_dec_and_del(struct klist_node *n) 153 { 154 return kref_put(&n->n_ref, klist_release); 155 } 156 157 /** 158 * klist_del - Decrement the reference count of node and try to remove. 159 * @n: node we're deleting. 160 */ 161 void klist_del(struct klist_node *n) 162 { 163 struct klist *k = n->n_klist; 164 void (*put)(struct klist_node *) = k->put; 165 166 spin_lock(&k->k_lock); 167 if (!klist_dec_and_del(n)) 168 put = NULL; 169 spin_unlock(&k->k_lock); 170 if (put) 171 put(n); 172 } 173 EXPORT_SYMBOL_GPL(klist_del); 174 175 /** 176 * klist_remove - Decrement the refcount of node and wait for it to go away. 177 * @n: node we're removing. 178 */ 179 void klist_remove(struct klist_node *n) 180 { 181 klist_del(n); 182 wait_for_completion(&n->n_removed); 183 } 184 EXPORT_SYMBOL_GPL(klist_remove); 185 186 /** 187 * klist_node_attached - Say whether a node is bound to a list or not. 188 * @n: Node that we're testing. 189 */ 190 int klist_node_attached(struct klist_node *n) 191 { 192 return (n->n_klist != NULL); 193 } 194 EXPORT_SYMBOL_GPL(klist_node_attached); 195 196 /** 197 * klist_iter_init_node - Initialize a klist_iter structure. 198 * @k: klist we're iterating. 199 * @i: klist_iter we're filling. 200 * @n: node to start with. 201 * 202 * Similar to klist_iter_init(), but starts the action off with @n, 203 * instead of with the list head. 204 */ 205 void klist_iter_init_node(struct klist *k, struct klist_iter *i, 206 struct klist_node *n) 207 { 208 i->i_klist = k; 209 i->i_head = &k->k_list; 210 i->i_cur = n; 211 if (n) 212 kref_get(&n->n_ref); 213 } 214 EXPORT_SYMBOL_GPL(klist_iter_init_node); 215 216 /** 217 * klist_iter_init - Iniitalize a klist_iter structure. 218 * @k: klist we're iterating. 219 * @i: klist_iter structure we're filling. 220 * 221 * Similar to klist_iter_init_node(), but start with the list head. 222 */ 223 void klist_iter_init(struct klist *k, struct klist_iter *i) 224 { 225 klist_iter_init_node(k, i, NULL); 226 } 227 EXPORT_SYMBOL_GPL(klist_iter_init); 228 229 /** 230 * klist_iter_exit - Finish a list iteration. 231 * @i: Iterator structure. 232 * 233 * Must be called when done iterating over list, as it decrements the 234 * refcount of the current node. Necessary in case iteration exited before 235 * the end of the list was reached, and always good form. 236 */ 237 void klist_iter_exit(struct klist_iter *i) 238 { 239 if (i->i_cur) { 240 klist_del(i->i_cur); 241 i->i_cur = NULL; 242 } 243 } 244 EXPORT_SYMBOL_GPL(klist_iter_exit); 245 246 static struct klist_node *to_klist_node(struct list_head *n) 247 { 248 return container_of(n, struct klist_node, n_node); 249 } 250 251 /** 252 * klist_next - Ante up next node in list. 253 * @i: Iterator structure. 254 * 255 * First grab list lock. Decrement the reference count of the previous 256 * node, if there was one. Grab the next node, increment its reference 257 * count, drop the lock, and return that next node. 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 EXPORT_SYMBOL_GPL(klist_next); 285