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         void (*put)(struct klist_node *) = n->n_klist->put;
 127         list_del(&n->n_node);
 128         complete(&n->n_removed);
 129         n->n_klist = NULL;
 130         if (put)
 131                 put(n);
 132 }
 133
 134 static int klist_dec_and_del(struct klist_node * n)
 135 {
 136         return kref_put(&n->n_ref, klist_release);
 137 }
 138
 139
 140 /**
 141  *      klist_del - Decrement the reference count of node and try to remove.
 142  *      @n:     node we're deleting.
 143  */
 144
 145 void klist_del(struct klist_node * n)
 146 {
 147         struct klist * k = n->n_klist;
 148
 149         spin_lock(&k->k_lock);
 150         klist_dec_and_del(n);
 151         spin_unlock(&k->k_lock);
 152 }
 153
 154 EXPORT_SYMBOL_GPL(klist_del);
 155
 156
 157 /**
 158  *      klist_remove - Decrement the refcount of node and wait for it to go away.
 159  *      @n:     node we're removing.
 160  */
 161
 162 void klist_remove(struct klist_node * n)
 163 {
 164         struct klist * k = n->n_klist;
 165         spin_lock(&k->k_lock);
 166         klist_dec_and_del(n);
 167         spin_unlock(&k->k_lock);
 168         wait_for_completion(&n->n_removed);
 169 }
 170
 171 EXPORT_SYMBOL_GPL(klist_remove);
 172
 173
 174 /**
 175  *      klist_node_attached - Say whether a node is bound to a list or not.
 176  *      @n:     Node that we're testing.
 177  */
 178
 179 int klist_node_attached(struct klist_node * n)
 180 {
 181         return (n->n_klist != NULL);
 182 }
 183
 184 EXPORT_SYMBOL_GPL(klist_node_attached);
 185
 186
 187 /**
 188  *      klist_iter_init_node - Initialize a klist_iter structure.
 189  *      @k:     klist we're iterating.
 190  *      @i:     klist_iter we're filling.
 191  *      @n:     node to start with.
 192  *
 193  *      Similar to klist_iter_init(), but starts the action off with @n,
 194  *      instead of with the list head.
 195  */
 196
 197 void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n)
 198 {
 199         i->i_klist = k;
 200         i->i_head = &k->k_list;
 201         i->i_cur = n;
 202         if (n)
 203                 kref_get(&n->n_ref);
 204 }
 205
 206 EXPORT_SYMBOL_GPL(klist_iter_init_node);
 207
 208
 209 /**
 210  *      klist_iter_init - Iniitalize a klist_iter structure.
 211  *      @k:     klist we're iterating.
 212  *      @i:     klist_iter structure we're filling.
 213  *
 214  *      Similar to klist_iter_init_node(), but start with the list head.
 215  */
 216
 217 void klist_iter_init(struct klist * k, struct klist_iter * i)
 218 {
 219         klist_iter_init_node(k, i, NULL);
 220 }
 221
 222 EXPORT_SYMBOL_GPL(klist_iter_init);
 223
 224
 225 /**
 226  *      klist_iter_exit - Finish a list iteration.
 227  *      @i:     Iterator structure.
 228  *
 229  *      Must be called when done iterating over list, as it decrements the
 230  *      refcount of the current node. Necessary in case iteration exited before
 231  *      the end of the list was reached, and always good form.
 232  */
 233
 234 void klist_iter_exit(struct klist_iter * i)
 235 {
 236         if (i->i_cur) {
 237                 klist_del(i->i_cur);
 238                 i->i_cur = NULL;
 239         }
 240 }
 241
 242 EXPORT_SYMBOL_GPL(klist_iter_exit);
 243
 244
 245 static struct klist_node * to_klist_node(struct list_head * n)
 246 {
 247         return container_of(n, struct klist_node, n_node);
 248 }
 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
 260 struct klist_node * klist_next(struct klist_iter * i)
 261 {
 262         struct list_head * next;
 263         struct klist_node * knode = NULL;
 264
 265         spin_lock(&i->i_klist->k_lock);
 266         if (i->i_cur) {
 267                 next = i->i_cur->n_node.next;
 268                 klist_dec_and_del(i->i_cur);
 269         } else
 270                 next = i->i_head->next;
 271
 272         if (next != i->i_head) {
 273                 knode = to_klist_node(next);
 274                 kref_get(&knode->n_ref);
 275         }
 276         i->i_cur = knode;
 277         spin_unlock(&i->i_klist->k_lock);
 278         return knode;
 279 }
 280
 281 EXPORT_SYMBOL_GPL(klist_next);
 282
 283