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