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  */
  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