lib/klist.c

   1 /*
   2  * klist.c - Routines for manipulating klists.
   3  *
   4  * Copyright (C) 2005 Patrick Mochel
   5  *
   6  * This file is released under the GPL v2.
   7  *
   8  * This klist interface provides a couple of structures that wrap around
   9  * struct list_head to provide explicit list "head" (struct klist) and list
  10  * "node" (struct klist_node) objects. For struct klist, a spinlock is
  11  * included that protects access to the actual list itself. struct
  12  * klist_node provides a pointer to the klist that owns it and a kref
  13  * reference count that indicates the number of current users of that node
  14  * in the list.
  15  *
  16  * The entire point is to provide an interface for iterating over a list
  17  * that is safe and allows for modification of the list during the
  18  * iteration (e.g. insertion and removal), including modification of the
  19  * current node on the list.
  20  *
  21  * It works using a 3rd object type - struct klist_iter - that is declared
  22  * and initialized before an iteration. klist_next() is used to acquire the
  23  * next element in the list. It returns NULL if there are no more items.
  24  * Internally, that routine takes the klist's lock, decrements the
  25  * reference count of the previous klist_node and increments the count of
  26  * the next klist_node. It then drops the lock and returns.
  27  *
  28  * There are primitives for adding and removing nodes to/from a klist.
  29  * When deleting, klist_del() will simply decrement the reference count.
  30  * Only when the count goes to 0 is the node removed from the list.
  31  * klist_remove() will try to delete the node from the list and block until
  32  * it is actually removed. This is useful for objects (like devices) that
  33  * have been removed from the system and must be freed (but must wait until
  34  * all accessors have finished).
  35  */
  36
  37 #include <linux/klist.h>
  38 #include <linux/module.h>
  39
  40 /*
  41  * Use the lowest bit of n_klist to mark deleted nodes and exclude
  42  * dead ones from iteration.
  43  */
  44 #define KNODE_DEAD              1LU
  45 #define KNODE_KLIST_MASK        ~KNODE_DEAD
  46
  47 static struct klist *knode_klist(struct klist_node *knode)
  48 {
  49         return (struct klist *)
  50                 ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
  51 }
  52
  53 static bool knode_dead(struct klist_node *knode)
  54 {
  55         return (unsigned long)knode->n_klist & KNODE_DEAD;
  56 }
  57
  58 static void knode_set_klist(struct klist_node *knode, struct klist *klist)
  59 {
  60         knode->n_klist = klist;
  61         /* no knode deserves to start its life dead */
  62         WARN_ON(knode_dead(knode));
  63 }
  64
  65 static void knode_kill(struct klist_node *knode)
  66 {
  67         /* and no knode should die twice ever either, see we're very humane */
  68         WARN_ON(knode_dead(knode));
  69         *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
  70 }
  71
  72 /**
  73  * klist_init - Initialize a klist structure.
  74  * @k: The klist we're initializing.
  75  * @get: The get function for the embedding object (NULL if none)
  76  * @put: The put function for the embedding object (NULL if none)
  77  *
  78  * Initialises the klist structure.  If the klist_node structures are
  79  * going to be embedded in refcounted objects (necessary for safe
  80  * deletion) then the get/put arguments are used to initialise
  81  * functions that take and release references on the embedding
  82  * objects.
  83  */
  84 void klist_init(struct klist *k, void (*get)(struct klist_node *),
  85                 void (*put)(struct klist_node *))
  86 {
  87         INIT_LIST_HEAD(&k->k_list);
  88         spin_lock_init(&k->k_lock);
  89         k->get = get;
  90         k->put = put;
  91 }
  92 EXPORT_SYMBOL_GPL(klist_init);
  93
  94 static void add_head(struct klist *k, struct klist_node *n)
  95 {
  96         spin_lock(&k->k_lock);
  97         list_add(&n->n_node, &k->k_list);
  98         spin_unlock(&k->k_lock);
  99 }
 100
 101 static void add_tail(struct klist *k, struct klist_node *n)
 102 {
 103         spin_lock(&k->k_lock);
 104         list_add_tail(&n->n_node, &k->k_list);
 105         spin_unlock(&k->k_lock);
 106 }
 107
 108 static void klist_node_init(struct klist *k, struct klist_node *n)
 109 {
 110         INIT_LIST_HEAD(&n->n_node);
 111         init_completion(&n->n_removed);
 112         kref_init(&n->n_ref);
 113         knode_set_klist(n, k);
 114         if (k->get)
 115                 k->get(n);
 116 }
 117
 118 /**
 119  * klist_add_head - Initialize a klist_node and add it to front.
 120  * @n: node we're adding.
 121  * @k: klist it's going on.
 122  */
 123 void klist_add_head(struct klist_node *n, struct klist *k)
 124 {
 125         klist_node_init(k, n);
 126         add_head(k, n);
 127 }
 128 EXPORT_SYMBOL_GPL(klist_add_head);
 129
 130 /**
 131  * klist_add_tail - Initialize a klist_node and add it to back.
 132  * @n: node we're adding.
 133  * @k: klist it's going on.
 134  */
 135 void klist_add_tail(struct klist_node *n, struct klist *k)
 136 {
 137         klist_node_init(k, n);
 138         add_tail(k, n);
 139 }
 140 EXPORT_SYMBOL_GPL(klist_add_tail);
 141
 142 /**
 143  * klist_add_after - Init a klist_node and add it after an existing node
 144  * @n: node we're adding.
 145  * @pos: node to put @n after
 146  */
 147 void klist_add_after(struct klist_node *n, struct klist_node *pos)
 148 {
 149         struct klist *k = knode_klist(pos);
 150
 151         klist_node_init(k, n);
 152         spin_lock(&k->k_lock);
 153         list_add(&n->n_node, &pos->n_node);
 154         spin_unlock(&k->k_lock);
 155 }
 156 EXPORT_SYMBOL_GPL(klist_add_after);
 157
 158 /**
 159  * klist_add_before - Init a klist_node and add it before an existing node
 160  * @n: node we're adding.
 161  * @pos: node to put @n after
 162  */
 163 void klist_add_before(struct klist_node *n, struct klist_node *pos)
 164 {
 165         struct klist *k = knode_klist(pos);
 166
 167         klist_node_init(k, n);
 168         spin_lock(&k->k_lock);
 169         list_add_tail(&n->n_node, &pos->n_node);
 170         spin_unlock(&k->k_lock);
 171 }
 172 EXPORT_SYMBOL_GPL(klist_add_before);
 173
 174 static void klist_release(struct kref *kref)
 175 {
 176         struct klist_node *n = container_of(kref, struct klist_node, n_ref);
 177
 178         WARN_ON(!knode_dead(n));
 179         list_del(&n->n_node);
 180         complete(&n->n_removed);
 181         knode_set_klist(n, NULL);
 182 }
 183
 184 static int klist_dec_and_del(struct klist_node *n)
 185 {
 186         return kref_put(&n->n_ref, klist_release);
 187 }
 188
 189 static void klist_put(struct klist_node *n, bool kill)
 190 {
 191         struct klist *k = knode_klist(n);
 192         void (*put)(struct klist_node *) = k->put;
 193
 194         spin_lock(&k->k_lock);
 195         if (kill)
 196                 knode_kill(n);
 197         if (!klist_dec_and_del(n))
 198                 put = NULL;
 199         spin_unlock(&k->k_lock);
 200         if (put)
 201                 put(n);
 202 }
 203
 204 /**
 205  * klist_del - Decrement the reference count of node and try to remove.
 206  * @n: node we're deleting.
 207  */
 208 void klist_del(struct klist_node *n)
 209 {
 210         klist_put(n, true);
 211 }
 212 EXPORT_SYMBOL_GPL(klist_del);
 213
 214 /**
 215  * klist_remove - Decrement the refcount of node and wait for it to go away.
 216  * @n: node we're removing.
 217  */
 218 void klist_remove(struct klist_node *n)
 219 {
 220         klist_del(n);
 221         wait_for_completion(&n->n_removed);
 222 }
 223 EXPORT_SYMBOL_GPL(klist_remove);
 224
 225 /**
 226  * klist_node_attached - Say whether a node is bound to a list or not.
 227  * @n: Node that we're testing.
 228  */
 229 int klist_node_attached(struct klist_node *n)
 230 {
 231         return (n->n_klist != NULL);
 232 }
 233 EXPORT_SYMBOL_GPL(klist_node_attached);
 234
 235 /**
 236  * klist_iter_init_node - Initialize a klist_iter structure.
 237  * @k: klist we're iterating.
 238  * @i: klist_iter we're filling.
 239  * @n: node to start with.
 240  *
 241  * Similar to klist_iter_init(), but starts the action off with @n,
 242  * instead of with the list head.
 243  */
 244 void klist_iter_init_node(struct klist *k, struct klist_iter *i,
 245                           struct klist_node *n)
 246 {
 247         i->i_klist = k;
 248         i->i_cur = n;
 249         if (n)
 250                 kref_get(&n->n_ref);
 251 }
 252 EXPORT_SYMBOL_GPL(klist_iter_init_node);
 253
 254 /**
 255  * klist_iter_init - Iniitalize a klist_iter structure.
 256  * @k: klist we're iterating.
 257  * @i: klist_iter structure we're filling.
 258  *
 259  * Similar to klist_iter_init_node(), but start with the list head.
 260  */
 261 void klist_iter_init(struct klist *k, struct klist_iter *i)
 262 {
 263         klist_iter_init_node(k, i, NULL);
 264 }
 265 EXPORT_SYMBOL_GPL(klist_iter_init);
 266
 267 /**
 268  * klist_iter_exit - Finish a list iteration.
 269  * @i: Iterator structure.
 270  *
 271  * Must be called when done iterating over list, as it decrements the
 272  * refcount of the current node. Necessary in case iteration exited before
 273  * the end of the list was reached, and always good form.
 274  */
 275 void klist_iter_exit(struct klist_iter *i)
 276 {
 277         if (i->i_cur) {
 278                 klist_put(i->i_cur, false);
 279                 i->i_cur = NULL;
 280         }
 281 }
 282 EXPORT_SYMBOL_GPL(klist_iter_exit);
 283
 284 static struct klist_node *to_klist_node(struct list_head *n)
 285 {
 286         return container_of(n, struct klist_node, n_node);
 287 }
 288
 289 /**
 290  * klist_next - Ante up next node in list.
 291  * @i: Iterator structure.
 292  *
 293  * First grab list lock. Decrement the reference count of the previous
 294  * node, if there was one. Grab the next node, increment its reference
 295  * count, drop the lock, and return that next node.
 296  */
 297 struct klist_node *klist_next(struct klist_iter *i)
 298 {
 299         void (*put)(struct klist_node *) = i->i_klist->put;
 300         struct klist_node *last = i->i_cur;
 301         struct klist_node *next;
 302
 303         spin_lock(&i->i_klist->k_lock);
 304
 305         if (last) {
 306                 next = to_klist_node(last->n_node.next);
 307                 if (!klist_dec_and_del(last))
 308                         put = NULL;
 309         } else
 310                 next = to_klist_node(i->i_klist->k_list.next);
 311
 312         i->i_cur = NULL;
 313         while (next != to_klist_node(&i->i_klist->k_list)) {
 314                 if (likely(!knode_dead(next))) {
 315                         kref_get(&next->n_ref);
 316                         i->i_cur = next;
 317                         break;
 318                 }
 319                 next = to_klist_node(next->n_node.next);
 320         }
 321
 322         spin_unlock(&i->i_klist->k_lock);
 323
 324         if (put && last)
 325                 put(last);
 326         return i->i_cur;
 327 }
 328 EXPORT_SYMBOL_GPL(klist_next);