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 }
 116
 117 static int klist_dec_and_del(struct klist_node * n)
 118 {
 119         return kref_put(&n->n_ref, klist_release);
 120 }
 121
 122
 123 /**
 124  *      klist_del - Decrement the reference count of node and try to remove.
 125  *      @n:     node we're deleting.
 126  */
 127
 128 void klist_del(struct klist_node * n)
 129 {
 130         struct klist * k = n->n_klist;
 131
 132         spin_lock(&k->k_lock);
 133         klist_dec_and_del(n);
 134         spin_unlock(&k->k_lock);
 135 }
 136
 137 EXPORT_SYMBOL_GPL(klist_del);
 138
 139
 140 /**
 141  *      klist_remove - Decrement the refcount of node and wait for it to go away.
 142  *      @n:     node we're removing.
 143  */
 144
 145 void klist_remove(struct klist_node * n)
 146 {
 147         spin_lock(&n->n_klist->k_lock);
 148         klist_dec_and_del(n);
 149         spin_unlock(&n->n_klist->k_lock);
 150         wait_for_completion(&n->n_removed);
 151 }
 152
 153 EXPORT_SYMBOL_GPL(klist_remove);
 154
 155
 156 /**
 157  *      klist_iter_init_node - Initialize a klist_iter structure.
 158  *      @k:     klist we're iterating.
 159  *      @i:     klist_iter we're filling.
 160  *      @n:     node to start with.
 161  *
 162  *      Similar to klist_iter_init(), but starts the action off with @n,
 163  *      instead of with the list head.
 164  */
 165
 166 void klist_iter_init_node(struct klist * k, struct klist_iter * i, struct klist_node * n)
 167 {
 168         i->i_klist = k;
 169         i->i_head = &k->k_list;
 170         i->i_cur = n;
 171 }
 172
 173 EXPORT_SYMBOL_GPL(klist_iter_init_node);
 174
 175
 176 /**
 177  *      klist_iter_init - Iniitalize a klist_iter structure.
 178  *      @k:     klist we're iterating.
 179  *      @i:     klist_iter structure we're filling.
 180  *
 181  *      Similar to klist_iter_init_node(), but start with the list head.
 182  */
 183
 184 void klist_iter_init(struct klist * k, struct klist_iter * i)
 185 {
 186         klist_iter_init_node(k, i, NULL);
 187 }
 188
 189 EXPORT_SYMBOL_GPL(klist_iter_init);
 190
 191
 192 /**
 193  *      klist_iter_exit - Finish a list iteration.
 194  *      @i:     Iterator structure.
 195  *
 196  *      Must be called when done iterating over list, as it decrements the
 197  *      refcount of the current node. Necessary in case iteration exited before
 198  *      the end of the list was reached, and always good form.
 199  */
 200
 201 void klist_iter_exit(struct klist_iter * i)
 202 {
 203         if (i->i_cur) {
 204                 klist_del(i->i_cur);
 205                 i->i_cur = NULL;
 206         }
 207 }
 208
 209 EXPORT_SYMBOL_GPL(klist_iter_exit);
 210
 211
 212 static struct klist_node * to_klist_node(struct list_head * n)
 213 {
 214         return container_of(n, struct klist_node, n_node);
 215 }
 216
 217
 218 /**
 219  *      klist_next - Ante up next node in list.
 220  *      @i:     Iterator structure.
 221  *
 222  *      First grab list lock. Decrement the reference count of the previous
 223  *      node, if there was one. Grab the next node, increment its reference
 224  *      count, drop the lock, and return that next node.
 225  */
 226
 227 struct klist_node * klist_next(struct klist_iter * i)
 228 {
 229         struct list_head * next;
 230         struct klist_node * knode = NULL;
 231
 232         spin_lock(&i->i_klist->k_lock);
 233         if (i->i_cur) {
 234                 next = i->i_cur->n_node.next;
 235                 klist_dec_and_del(i->i_cur);
 236         } else
 237                 next = i->i_head->next;
 238
 239         if (next != i->i_head) {
 240                 knode = to_klist_node(next);
 241                 kref_get(&knode->n_ref);
 242         }
 243         i->i_cur = knode;
 244         spin_unlock(&i->i_klist->k_lock);
 245         return knode;
 246 }
 247
 248 EXPORT_SYMBOL_GPL(klist_next);