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 void (*put)(struct klist_node *) = n->n_klist->put; 127 list_del(&n->n_node); 128 complete(&n->n_removed); 129 n->n_klist = NULL; 130 if (put) 131 put(n); 132 } 133 134 static int klist_dec_and_del(struct klist_node * n) 135 { 136 return kref_put(&n->n_ref, klist_release); 137 } 138 139 140 /** 141 * klist_del - Decrement the reference count of node and try to remove. 142 * @n: node we're deleting. 143 */ 144 145 void klist_del(struct klist_node * n) 146 { 147 struct klist * k = n->n_klist; 148 149 spin_lock(&k->k_lock); 150 klist_dec_and_del(n); 151 spin_unlock(&k->k_lock); 152 } 153 154 EXPORT_SYMBOL_GPL(klist_del); 155 156 157 /** 158 * klist_remove - Decrement the refcount of node and wait for it to go away. 159 * @n: node we're removing. 160 */ 161 162 void klist_remove(struct klist_node * n) 163 { 164 struct klist * k = n->n_klist; 165 spin_lock(&k->k_lock); 166 klist_dec_and_del(n); 167 spin_unlock(&k->k_lock); 168 wait_for_completion(&n->n_removed); 169 } 170 171 EXPORT_SYMBOL_GPL(klist_remove); 172 173 174 /** 175 * klist_node_attached - Say whether a node is bound to a list or not. 176 * @n: Node that we're testing. 177 */ 178 179 int klist_node_attached(struct klist_node * n) 180 { 181 return (n->n_klist != NULL); 182 } 183 184 EXPORT_SYMBOL_GPL(klist_node_attached); 185 186 187 /** 188 * klist_iter_init_node - Initialize a klist_iter structure. 189 * @k: klist we're iterating. 190 * @i: klist_iter we're filling. 191 * @n: node to start with. 192 * 193 * Similar to klist_iter_init(), but starts the action off with @n, 194 * instead of with the list head. 195 */ 196 197 void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n) 198 { 199 i->i_klist = k; 200 i->i_head = &k->k_list; 201 i->i_cur = n; 202 if (n) 203 kref_get(&n->n_ref); 204 } 205 206 EXPORT_SYMBOL_GPL(klist_iter_init_node); 207 208 209 /** 210 * klist_iter_init - Iniitalize a klist_iter structure. 211 * @k: klist we're iterating. 212 * @i: klist_iter structure we're filling. 213 * 214 * Similar to klist_iter_init_node(), but start with the list head. 215 */ 216 217 void klist_iter_init(struct klist * k, struct klist_iter * i) 218 { 219 klist_iter_init_node(k, i, NULL); 220 } 221 222 EXPORT_SYMBOL_GPL(klist_iter_init); 223 224 225 /** 226 * klist_iter_exit - Finish a list iteration. 227 * @i: Iterator structure. 228 * 229 * Must be called when done iterating over list, as it decrements the 230 * refcount of the current node. Necessary in case iteration exited before 231 * the end of the list was reached, and always good form. 232 */ 233 234 void klist_iter_exit(struct klist_iter * i) 235 { 236 if (i->i_cur) { 237 klist_del(i->i_cur); 238 i->i_cur = NULL; 239 } 240 } 241 242 EXPORT_SYMBOL_GPL(klist_iter_exit); 243 244 245 static struct klist_node * to_klist_node(struct list_head * n) 246 { 247 return container_of(n, struct klist_node, n_node); 248 } 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 */ 259 260 struct klist_node * klist_next(struct klist_iter * i) 261 { 262 struct list_head * next; 263 struct klist_node * knode = NULL; 264 265 spin_lock(&i->i_klist->k_lock); 266 if (i->i_cur) { 267 next = i->i_cur->n_node.next; 268 klist_dec_and_del(i->i_cur); 269 } else 270 next = i->i_head->next; 271 272 if (next != i->i_head) { 273 knode = to_klist_node(next); 274 kref_get(&knode->n_ref); 275 } 276 i->i_cur = knode; 277 spin_unlock(&i->i_klist->k_lock); 278 return knode; 279 } 280 281 EXPORT_SYMBOL_GPL(klist_next); 282 283 284