lib/klist.c

   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);