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 */ 46 47 void klist_init(struct klist * k) 48 { 49 INIT_LIST_HEAD(&k->k_list); 50 spin_lock_init(&k->k_lock); 51 } 52 53 EXPORT_SYMBOL_GPL(klist_init); 54 55 56 static void add_head(struct klist * k, struct klist_node * n) 57 { 58 spin_lock(&k->k_lock); 59 list_add(&n->n_node, &k->k_list); 60 spin_unlock(&k->k_lock); 61 } 62 63 static void add_tail(struct klist * k, struct klist_node * n) 64 { 65 spin_lock(&k->k_lock); 66 list_add_tail(&n->n_node, &k->k_list); 67 spin_unlock(&k->k_lock); 68 } 69 70 71 static void klist_node_init(struct klist * k, struct klist_node * n) 72 { 73 INIT_LIST_HEAD(&n->n_node); 74 init_completion(&n->n_removed); 75 kref_init(&n->n_ref); 76 n->n_klist = k; 77 } 78 79 80 /** 81 * klist_add_head - Initialize a klist_node and add it to front. 82 * @k: klist it's going on. 83 * @n: node we're adding. 84 */ 85 86 void klist_add_head(struct klist * k, struct klist_node * n) 87 { 88 klist_node_init(k, n); 89 add_head(k, n); 90 } 91 92 EXPORT_SYMBOL_GPL(klist_add_head); 93 94 95 /** 96 * klist_add_tail - Initialize a klist_node and add it to back. 97 * @k: klist it's going on. 98 * @n: node we're adding. 99 */ 100 101 void klist_add_tail(struct klist * k, struct klist_node * n) 102 { 103 klist_node_init(k, n); 104 add_tail(k, n); 105 } 106 107 EXPORT_SYMBOL_GPL(klist_add_tail); 108 109 110 static void klist_release(struct kref * kref) 111 { 112 struct klist_node * n = container_of(kref, struct klist_node, n_ref); 113 list_del(&n->n_node); 114 complete(&n->n_removed); 115 n->n_klist = NULL; 116 } 117 118 static int klist_dec_and_del(struct klist_node * n) 119 { 120 return kref_put(&n->n_ref, klist_release); 121 } 122 123 124 /** 125 * klist_del - Decrement the reference count of node and try to remove. 126 * @n: node we're deleting. 127 */ 128 129 void klist_del(struct klist_node * n) 130 { 131 struct klist * k = n->n_klist; 132 133 spin_lock(&k->k_lock); 134 klist_dec_and_del(n); 135 spin_unlock(&k->k_lock); 136 } 137 138 EXPORT_SYMBOL_GPL(klist_del); 139 140 141 /** 142 * klist_remove - Decrement the refcount of node and wait for it to go away. 143 * @n: node we're removing. 144 */ 145 146 void klist_remove(struct klist_node * n) 147 { 148 struct klist * k = n->n_klist; 149 spin_lock(&k->k_lock); 150 klist_dec_and_del(n); 151 spin_unlock(&k->k_lock); 152 wait_for_completion(&n->n_removed); 153 } 154 155 EXPORT_SYMBOL_GPL(klist_remove); 156 157 158 /** 159 * klist_node_attached - Say whether a node is bound to a list or not. 160 * @n: Node that we're testing. 161 */ 162 163 int klist_node_attached(struct klist_node * n) 164 { 165 return (n->n_klist != NULL); 166 } 167 168 EXPORT_SYMBOL_GPL(klist_node_attached); 169 170 171 /** 172 * klist_iter_init_node - Initialize a klist_iter structure. 173 * @k: klist we're iterating. 174 * @i: klist_iter we're filling. 175 * @n: node to start with. 176 * 177 * Similar to klist_iter_init(), but starts the action off with @n, 178 * instead of with the list head. 179 */ 180 181 void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n) 182 { 183 i->i_klist = k; 184 i->i_head = &k->k_list; 185 i->i_cur = n; 186 } 187 188 EXPORT_SYMBOL_GPL(klist_iter_init_node); 189 190 191 /** 192 * klist_iter_init - Iniitalize a klist_iter structure. 193 * @k: klist we're iterating. 194 * @i: klist_iter structure we're filling. 195 * 196 * Similar to klist_iter_init_node(), but start with the list head. 197 */ 198 199 void klist_iter_init(struct klist * k, struct klist_iter * i) 200 { 201 klist_iter_init_node(k, i, NULL); 202 } 203 204 EXPORT_SYMBOL_GPL(klist_iter_init); 205 206 207 /** 208 * klist_iter_exit - Finish a list iteration. 209 * @i: Iterator structure. 210 * 211 * Must be called when done iterating over list, as it decrements the 212 * refcount of the current node. Necessary in case iteration exited before 213 * the end of the list was reached, and always good form. 214 */ 215 216 void klist_iter_exit(struct klist_iter * i) 217 { 218 if (i->i_cur) { 219 klist_del(i->i_cur); 220 i->i_cur = NULL; 221 } 222 } 223 224 EXPORT_SYMBOL_GPL(klist_iter_exit); 225 226 227 static struct klist_node * to_klist_node(struct list_head * n) 228 { 229 return container_of(n, struct klist_node, n_node); 230 } 231 232 233 /** 234 * klist_next - Ante up next node in list. 235 * @i: Iterator structure. 236 * 237 * First grab list lock. Decrement the reference count of the previous 238 * node, if there was one. Grab the next node, increment its reference 239 * count, drop the lock, and return that next node. 240 */ 241 242 struct klist_node * klist_next(struct klist_iter * i) 243 { 244 struct list_head * next; 245 struct klist_node * knode = NULL; 246 247 spin_lock(&i->i_klist->k_lock); 248 if (i->i_cur) { 249 next = i->i_cur->n_node.next; 250 klist_dec_and_del(i->i_cur); 251 } else 252 next = i->i_head->next; 253 254 if (next != i->i_head) { 255 knode = to_klist_node(next); 256 kref_get(&knode->n_ref); 257 } 258 i->i_cur = knode; 259 spin_unlock(&i->i_klist->k_lock); 260 return knode; 261 } 262 263 EXPORT_SYMBOL_GPL(klist_next); 264 265 266