lib/klist.c

   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 /**
 124  * klist_add_after - Init a klist_node and add it after an existing node
 125  * @n: node we're adding.
 126  * @pos: node to put @n after
 127  */
 128 void klist_add_after(struct klist_node *n, struct klist_node *pos)
 129 {
 130         struct klist *k = pos->n_klist;
 131
 132         klist_node_init(k, n);
 133         spin_lock(&k->k_lock);
 134         list_add(&n->n_node, &pos->n_node);
 135         spin_unlock(&k->k_lock);
 136 }
 137 EXPORT_SYMBOL_GPL(klist_add_after);
 138
 139 /**
 140  * klist_add_before - Init a klist_node and add it before an existing node
 141  * @n: node we're adding.
 142  * @pos: node to put @n after
 143  */
 144 void klist_add_before(struct klist_node *n, struct klist_node *pos)
 145 {
 146         struct klist *k = pos->n_klist;
 147
 148         klist_node_init(k, n);
 149         spin_lock(&k->k_lock);
 150         list_add_tail(&n->n_node, &pos->n_node);
 151         spin_unlock(&k->k_lock);
 152 }
 153 EXPORT_SYMBOL_GPL(klist_add_before);
 154
 155
 156 static void klist_release(struct kref * kref)
 157 {
 158         struct klist_node * n = container_of(kref, struct klist_node, n_ref);
 159
 160         list_del(&n->n_node);
 161         complete(&n->n_removed);
 162         n->n_klist = NULL;
 163 }
 164
 165 static int klist_dec_and_del(struct klist_node * n)
 166 {
 167         return kref_put(&n->n_ref, klist_release);
 168 }
 169
 170
 171 /**
 172  *      klist_del - Decrement the reference count of node and try to remove.
 173  *      @n:     node we're deleting.
 174  */
 175
 176 void klist_del(struct klist_node * n)
 177 {
 178         struct klist * k = n->n_klist;
 179         void (*put)(struct klist_node *) = k->put;
 180
 181         spin_lock(&k->k_lock);
 182         if (!klist_dec_and_del(n))
 183                 put = NULL;
 184         spin_unlock(&k->k_lock);
 185         if (put)
 186                 put(n);
 187 }
 188
 189 EXPORT_SYMBOL_GPL(klist_del);
 190
 191
 192 /**
 193  *      klist_remove - Decrement the refcount of node and wait for it to go away.
 194  *      @n:     node we're removing.
 195  */
 196
 197 void klist_remove(struct klist_node * n)
 198 {
 199         klist_del(n);
 200         wait_for_completion(&n->n_removed);
 201 }
 202
 203 EXPORT_SYMBOL_GPL(klist_remove);
 204
 205
 206 /**
 207  *      klist_node_attached - Say whether a node is bound to a list or not.
 208  *      @n:     Node that we're testing.
 209  */
 210
 211 int klist_node_attached(struct klist_node * n)
 212 {
 213         return (n->n_klist != NULL);
 214 }
 215
 216 EXPORT_SYMBOL_GPL(klist_node_attached);
 217
 218
 219 /**
 220  *      klist_iter_init_node - Initialize a klist_iter structure.
 221  *      @k:     klist we're iterating.
 222  *      @i:     klist_iter we're filling.
 223  *      @n:     node to start with.
 224  *
 225  *      Similar to klist_iter_init(), but starts the action off with @n,
 226  *      instead of with the list head.
 227  */
 228
 229 void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n)
 230 {
 231         i->i_klist = k;
 232         i->i_head = &k->k_list;
 233         i->i_cur = n;
 234         if (n)
 235                 kref_get(&n->n_ref);
 236 }
 237
 238 EXPORT_SYMBOL_GPL(klist_iter_init_node);
 239
 240
 241 /**
 242  *      klist_iter_init - Iniitalize a klist_iter structure.
 243  *      @k:     klist we're iterating.
 244  *      @i:     klist_iter structure we're filling.
 245  *
 246  *      Similar to klist_iter_init_node(), but start with the list head.
 247  */
 248
 249 void klist_iter_init(struct klist * k, struct klist_iter * i)
 250 {
 251         klist_iter_init_node(k, i, NULL);
 252 }
 253
 254 EXPORT_SYMBOL_GPL(klist_iter_init);
 255
 256
 257 /**
 258  *      klist_iter_exit - Finish a list iteration.
 259  *      @i:     Iterator structure.
 260  *
 261  *      Must be called when done iterating over list, as it decrements the
 262  *      refcount of the current node. Necessary in case iteration exited before
 263  *      the end of the list was reached, and always good form.
 264  */
 265
 266 void klist_iter_exit(struct klist_iter * i)
 267 {
 268         if (i->i_cur) {
 269                 klist_del(i->i_cur);
 270                 i->i_cur = NULL;
 271         }
 272 }
 273
 274 EXPORT_SYMBOL_GPL(klist_iter_exit);
 275
 276
 277 static struct klist_node * to_klist_node(struct list_head * n)
 278 {
 279         return container_of(n, struct klist_node, n_node);
 280 }
 281
 282
 283 /**
 284  *      klist_next - Ante up next node in list.
 285  *      @i:     Iterator structure.
 286  *
 287  *      First grab list lock. Decrement the reference count of the previous
 288  *      node, if there was one. Grab the next node, increment its reference
 289  *      count, drop the lock, and return that next node.
 290  */
 291
 292 struct klist_node * klist_next(struct klist_iter * i)
 293 {
 294         struct list_head * next;
 295         struct klist_node * lnode = i->i_cur;
 296         struct klist_node * knode = NULL;
 297         void (*put)(struct klist_node *) = i->i_klist->put;
 298
 299         spin_lock(&i->i_klist->k_lock);
 300         if (lnode) {
 301                 next = lnode->n_node.next;
 302                 if (!klist_dec_and_del(lnode))
 303                         put = NULL;
 304         } else
 305                 next = i->i_head->next;
 306
 307         if (next != i->i_head) {
 308                 knode = to_klist_node(next);
 309                 kref_get(&knode->n_ref);
 310         }
 311         i->i_cur = knode;
 312         spin_unlock(&i->i_klist->k_lock);
 313         if (put && lnode)
 314                 put(lnode);
 315         return knode;
 316 }
 317
 318 EXPORT_SYMBOL_GPL(klist_next);
 319
 320