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 * Use the lowest bit of n_klist to mark deleted nodes and exclude 42 * dead ones from iteration. 43 */ 44 #define KNODE_DEAD 1LU 45 #define KNODE_KLIST_MASK ~KNODE_DEAD 46 47 static struct klist *knode_klist(struct klist_node *knode) 48 { 49 return (struct klist *) 50 ((unsigned long)knode->n_klist & KNODE_KLIST_MASK); 51 } 52 53 static bool knode_dead(struct klist_node *knode) 54 { 55 return (unsigned long)knode->n_klist & KNODE_DEAD; 56 } 57 58 static void knode_set_klist(struct klist_node *knode, struct klist *klist) 59 { 60 knode->n_klist = klist; 61 /* no knode deserves to start its life dead */ 62 WARN_ON(knode_dead(knode)); 63 } 64 65 static void knode_kill(struct klist_node *knode) 66 { 67 /* and no knode should die twice ever either, see we're very humane */ 68 WARN_ON(knode_dead(knode)); 69 *(unsigned long *)&knode->n_klist |= KNODE_DEAD; 70 } 71 72 /** 73 * klist_init - Initialize a klist structure. 74 * @k: The klist we're initializing. 75 * @get: The get function for the embedding object (NULL if none) 76 * @put: The put function for the embedding object (NULL if none) 77 * 78 * Initialises the klist structure. If the klist_node structures are 79 * going to be embedded in refcounted objects (necessary for safe 80 * deletion) then the get/put arguments are used to initialise 81 * functions that take and release references on the embedding 82 * objects. 83 */ 84 void klist_init(struct klist *k, void (*get)(struct klist_node *), 85 void (*put)(struct klist_node *)) 86 { 87 INIT_LIST_HEAD(&k->k_list); 88 spin_lock_init(&k->k_lock); 89 k->get = get; 90 k->put = put; 91 } 92 EXPORT_SYMBOL_GPL(klist_init); 93 94 static void add_head(struct klist *k, struct klist_node *n) 95 { 96 spin_lock(&k->k_lock); 97 list_add(&n->n_node, &k->k_list); 98 spin_unlock(&k->k_lock); 99 } 100 101 static void add_tail(struct klist *k, struct klist_node *n) 102 { 103 spin_lock(&k->k_lock); 104 list_add_tail(&n->n_node, &k->k_list); 105 spin_unlock(&k->k_lock); 106 } 107 108 static void klist_node_init(struct klist *k, struct klist_node *n) 109 { 110 INIT_LIST_HEAD(&n->n_node); 111 init_completion(&n->n_removed); 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 */ 123 void klist_add_head(struct klist_node *n, struct klist *k) 124 { 125 klist_node_init(k, n); 126 add_head(k, n); 127 } 128 EXPORT_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 */ 135 void klist_add_tail(struct klist_node *n, struct klist *k) 136 { 137 klist_node_init(k, n); 138 add_tail(k, n); 139 } 140 EXPORT_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 */ 147 void 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 } 156 EXPORT_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 */ 163 void 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 } 172 EXPORT_SYMBOL_GPL(klist_add_before); 173 174 static void klist_release(struct kref *kref) 175 { 176 struct klist_node *n = container_of(kref, struct klist_node, n_ref); 177 178 WARN_ON(!knode_dead(n)); 179 list_del(&n->n_node); 180 complete(&n->n_removed); 181 knode_set_klist(n, NULL); 182 } 183 184 static int klist_dec_and_del(struct klist_node *n) 185 { 186 return kref_put(&n->n_ref, klist_release); 187 } 188 189 static void klist_put(struct klist_node *n, bool kill) 190 { 191 struct klist *k = knode_klist(n); 192 void (*put)(struct klist_node *) = k->put; 193 194 spin_lock(&k->k_lock); 195 if (kill) 196 knode_kill(n); 197 if (!klist_dec_and_del(n)) 198 put = NULL; 199 spin_unlock(&k->k_lock); 200 if (put) 201 put(n); 202 } 203 204 /** 205 * klist_del - Decrement the reference count of node and try to remove. 206 * @n: node we're deleting. 207 */ 208 void klist_del(struct klist_node *n) 209 { 210 klist_put(n, true); 211 } 212 EXPORT_SYMBOL_GPL(klist_del); 213 214 /** 215 * klist_remove - Decrement the refcount of node and wait for it to go away. 216 * @n: node we're removing. 217 */ 218 void klist_remove(struct klist_node *n) 219 { 220 klist_del(n); 221 wait_for_completion(&n->n_removed); 222 } 223 EXPORT_SYMBOL_GPL(klist_remove); 224 225 /** 226 * klist_node_attached - Say whether a node is bound to a list or not. 227 * @n: Node that we're testing. 228 */ 229 int klist_node_attached(struct klist_node *n) 230 { 231 return (n->n_klist != NULL); 232 } 233 EXPORT_SYMBOL_GPL(klist_node_attached); 234 235 /** 236 * klist_iter_init_node - Initialize a klist_iter structure. 237 * @k: klist we're iterating. 238 * @i: klist_iter we're filling. 239 * @n: node to start with. 240 * 241 * Similar to klist_iter_init(), but starts the action off with @n, 242 * instead of with the list head. 243 */ 244 void klist_iter_init_node(struct klist *k, struct klist_iter *i, 245 struct klist_node *n) 246 { 247 i->i_klist = k; 248 i->i_cur = n; 249 if (n) 250 kref_get(&n->n_ref); 251 } 252 EXPORT_SYMBOL_GPL(klist_iter_init_node); 253 254 /** 255 * klist_iter_init - Iniitalize a klist_iter structure. 256 * @k: klist we're iterating. 257 * @i: klist_iter structure we're filling. 258 * 259 * Similar to klist_iter_init_node(), but start with the list head. 260 */ 261 void klist_iter_init(struct klist *k, struct klist_iter *i) 262 { 263 klist_iter_init_node(k, i, NULL); 264 } 265 EXPORT_SYMBOL_GPL(klist_iter_init); 266 267 /** 268 * klist_iter_exit - Finish a list iteration. 269 * @i: Iterator structure. 270 * 271 * Must be called when done iterating over list, as it decrements the 272 * refcount of the current node. Necessary in case iteration exited before 273 * the end of the list was reached, and always good form. 274 */ 275 void klist_iter_exit(struct klist_iter *i) 276 { 277 if (i->i_cur) { 278 klist_put(i->i_cur, false); 279 i->i_cur = NULL; 280 } 281 } 282 EXPORT_SYMBOL_GPL(klist_iter_exit); 283 284 static struct klist_node *to_klist_node(struct list_head *n) 285 { 286 return container_of(n, struct klist_node, n_node); 287 } 288 289 /** 290 * klist_next - Ante up next node in list. 291 * @i: Iterator structure. 292 * 293 * First grab list lock. Decrement the reference count of the previous 294 * node, if there was one. Grab the next node, increment its reference 295 * count, drop the lock, and return that next node. 296 */ 297 struct klist_node *klist_next(struct klist_iter *i) 298 { 299 void (*put)(struct klist_node *) = i->i_klist->put; 300 struct klist_node *last = i->i_cur; 301 struct klist_node *next; 302 303 spin_lock(&i->i_klist->k_lock); 304 305 if (last) { 306 next = to_klist_node(last->n_node.next); 307 if (!klist_dec_and_del(last)) 308 put = NULL; 309 } else 310 next = to_klist_node(i->i_klist->k_list.next); 311 312 i->i_cur = NULL; 313 while (next != to_klist_node(&i->i_klist->k_list)) { 314 if (likely(!knode_dead(next))) { 315 kref_get(&next->n_ref); 316 i->i_cur = next; 317 break; 318 } 319 next = to_klist_node(next->n_node.next); 320 } 321 322 spin_unlock(&i->i_klist->k_lock); 323 324 if (put && last) 325 put(last); 326 return i->i_cur; 327 } 328 EXPORT_SYMBOL_GPL(klist_next); 329