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 static void klist_release(struct kref * kref)
 124 {
 125         struct klist_node * n = container_of(kref, struct klist_node, n_ref);
 126
 127         list_del(&n->n_node);
 128         complete(&n->n_removed);
 129         n->n_klist = NULL;
 130 }
 131
 132 static int klist_dec_and_del(struct klist_node * n)
 133 {
 134         return kref_put(&n->n_ref, klist_release);
 135 }
 136
 137
 138 /**
 139  *      klist_del - Decrement the reference count of node and try to remove.
 140  *      @n:     node we're deleting.
 141  */
 142
 143 void klist_del(struct klist_node * n)
 144 {
 145         struct klist * k = n->n_klist;
 146         void (*put)(struct klist_node *) = k->put;
 147
 148         spin_lock(&k->k_lock);
 149         if (!klist_dec_and_del(n))
 150                 put = NULL;
 151         spin_unlock(&k->k_lock);
 152         if (put)
 153                 put(n);
 154 }
 155
 156 EXPORT_SYMBOL_GPL(klist_del);
 157
 158
 159 /**
 160  *      klist_remove - Decrement the refcount of node and wait for it to go away.
 161  *      @n:     node we're removing.
 162  */
 163
 164 void klist_remove(struct klist_node * n)
 165 {
 166         klist_del(n);
 167         wait_for_completion(&n->n_removed);
 168 }
 169
 170 EXPORT_SYMBOL_GPL(klist_remove);
 171
 172
 173 /**
 174  *      klist_node_attached - Say whether a node is bound to a list or not.
 175  *      @n:     Node that we're testing.
 176  */
 177
 178 int klist_node_attached(struct klist_node * n)
 179 {
 180         return (n->n_klist != NULL);
 181 }
 182
 183 EXPORT_SYMBOL_GPL(klist_node_attached);
 184
 185
 186 /**
 187  *      klist_iter_init_node - Initialize a klist_iter structure.
 188  *      @k:     klist we're iterating.
 189  *      @i:     klist_iter we're filling.
 190  *      @n:     node to start with.
 191  *
 192  *      Similar to klist_iter_init(), but starts the action off with @n,
 193  *      instead of with the list head.
 194  */
 195
 196 void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n)
 197 {
 198         i->i_klist = k;
 199         i->i_head = &k->k_list;
 200         i->i_cur = n;
 201         if (n)
 202                 kref_get(&n->n_ref);
 203 }
 204
 205 EXPORT_SYMBOL_GPL(klist_iter_init_node);
 206
 207
 208 /**
 209  *      klist_iter_init - Iniitalize a klist_iter structure.
 210  *      @k:     klist we're iterating.
 211  *      @i:     klist_iter structure we're filling.
 212  *
 213  *      Similar to klist_iter_init_node(), but start with the list head.
 214  */
 215
 216 void klist_iter_init(struct klist * k, struct klist_iter * i)
 217 {
 218         klist_iter_init_node(k, i, NULL);
 219 }
 220
 221 EXPORT_SYMBOL_GPL(klist_iter_init);
 222
 223
 224 /**
 225  *      klist_iter_exit - Finish a list iteration.
 226  *      @i:     Iterator structure.
 227  *
 228  *      Must be called when done iterating over list, as it decrements the
 229  *      refcount of the current node. Necessary in case iteration exited before
 230  *      the end of the list was reached, and always good form.
 231  */
 232
 233 void klist_iter_exit(struct klist_iter * i)
 234 {
 235         if (i->i_cur) {
 236                 klist_del(i->i_cur);
 237                 i->i_cur = NULL;
 238         }
 239 }
 240
 241 EXPORT_SYMBOL_GPL(klist_iter_exit);
 242
 243
 244 static struct klist_node * to_klist_node(struct list_head * n)
 245 {
 246         return container_of(n, struct klist_node, n_node);
 247 }
 248
 249
 250 /**
 251  *      klist_next - Ante up next node in list.
 252  *      @i:     Iterator structure.
 253  *
 254  *      First grab list lock. Decrement the reference count of the previous
 255  *      node, if there was one. Grab the next node, increment its reference
 256  *      count, drop the lock, and return that next node.
 257  */
 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
 285 EXPORT_SYMBOL_GPL(klist_next);
 286
 287