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/export.h>
  39 #include <linux/sched.h>
  40
  41 /*
  42  * Use the lowest bit of n_klist to mark deleted nodes and exclude
  43  * dead ones from iteration.
  44  */
  45 #define KNODE_DEAD              1LU
  46 #define KNODE_KLIST_MASK        ~KNODE_DEAD
  47
  48 static struct klist *knode_klist(struct klist_node *knode)
  49 {
  50         return (struct klist *)
  51                 ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
  52 }
  53
  54 static bool knode_dead(struct klist_node *knode)
  55 {
  56         return (unsigned long)knode->n_klist & KNODE_DEAD;
  57 }
  58
  59 static void knode_set_klist(struct klist_node *knode, struct klist *klist)
  60 {
  61         knode->n_klist = klist;
  62         /* no knode deserves to start its life dead */
  63         WARN_ON(knode_dead(knode));
  64 }
  65
  66 static void knode_kill(struct klist_node *knode)
  67 {
  68         /* and no knode should die twice ever either, see we're very humane */
  69         WARN_ON(knode_dead(knode));
  70         *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
  71 }
  72
  73 /**
  74  * klist_init - Initialize a klist structure.
  75  * @k: The klist we're initializing.
  76  * @get: The get function for the embedding object (NULL if none)
  77  * @put: The put function for the embedding object (NULL if none)
  78  *
  79  * Initialises the klist structure.  If the klist_node structures are
  80  * going to be embedded in refcounted objects (necessary for safe
  81  * deletion) then the get/put arguments are used to initialise
  82  * functions that take and release references on the embedding
  83  * objects.
  84  */
  85 void klist_init(struct klist *k, void (*get)(struct klist_node *),
  86                 void (*put)(struct klist_node *))
  87 {
  88         INIT_LIST_HEAD(&k->k_list);
  89         spin_lock_init(&k->k_lock);
  90         k->get = get;
  91         k->put = put;
  92 }
  93 EXPORT_SYMBOL_GPL(klist_init);
  94
  95 static void add_head(struct klist *k, struct klist_node *n)
  96 {
  97         spin_lock(&k->k_lock);
  98         list_add(&n->n_node, &k->k_list);
  99         spin_unlock(&k->k_lock);
 100 }
 101
 102 static void add_tail(struct klist *k, struct klist_node *n)
 103 {
 104         spin_lock(&k->k_lock);
 105         list_add_tail(&n->n_node, &k->k_list);
 106         spin_unlock(&k->k_lock);
 107 }
 108
 109 static void klist_node_init(struct klist *k, struct klist_node *n)
 110 {
 111         INIT_LIST_HEAD(&n->n_node);
 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 struct klist_waiter {
 175         struct list_head list;
 176         struct klist_node *node;
 177         struct task_struct *process;
 178         int woken;
 179 };
 180
 181 static DEFINE_SPINLOCK(klist_remove_lock);
 182 static LIST_HEAD(klist_remove_waiters);
 183
 184 static void klist_release(struct kref *kref)
 185 {
 186         struct klist_waiter *waiter, *tmp;
 187         struct klist_node *n = container_of(kref, struct klist_node, n_ref);
 188
 189         WARN_ON(!knode_dead(n));
 190         list_del(&n->n_node);
 191         spin_lock(&klist_remove_lock);
 192         list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
 193                 if (waiter->node != n)
 194                         continue;
 195
 196                 list_del(&waiter->list);
 197                 waiter->woken = 1;
 198                 mb();
 199                 wake_up_process(waiter->process);
 200         }
 201         spin_unlock(&klist_remove_lock);
 202         knode_set_klist(n, NULL);
 203 }
 204
 205 static int klist_dec_and_del(struct klist_node *n)
 206 {
 207         return kref_put(&n->n_ref, klist_release);
 208 }
 209
 210 static void klist_put(struct klist_node *n, bool kill)
 211 {
 212         struct klist *k = knode_klist(n);
 213         void (*put)(struct klist_node *) = k->put;
 214
 215         spin_lock(&k->k_lock);
 216         if (kill)
 217                 knode_kill(n);
 218         if (!klist_dec_and_del(n))
 219                 put = NULL;
 220         spin_unlock(&k->k_lock);
 221         if (put)
 222                 put(n);
 223 }
 224
 225 /**
 226  * klist_del - Decrement the reference count of node and try to remove.
 227  * @n: node we're deleting.
 228  */
 229 void klist_del(struct klist_node *n)
 230 {
 231         klist_put(n, true);
 232 }
 233 EXPORT_SYMBOL_GPL(klist_del);
 234
 235 /**
 236  * klist_remove - Decrement the refcount of node and wait for it to go away.
 237  * @n: node we're removing.
 238  */
 239 void klist_remove(struct klist_node *n)
 240 {
 241         struct klist_waiter waiter;
 242
 243         waiter.node = n;
 244         waiter.process = current;
 245         waiter.woken = 0;
 246         spin_lock(&klist_remove_lock);
 247         list_add(&waiter.list, &klist_remove_waiters);
 248         spin_unlock(&klist_remove_lock);
 249
 250         klist_del(n);
 251
 252         for (;;) {
 253                 set_current_state(TASK_UNINTERRUPTIBLE);
 254                 if (waiter.woken)
 255                         break;
 256                 schedule();
 257         }
 258         __set_current_state(TASK_RUNNING);
 259 }
 260 EXPORT_SYMBOL_GPL(klist_remove);
 261
 262 /**
 263  * klist_node_attached - Say whether a node is bound to a list or not.
 264  * @n: Node that we're testing.
 265  */
 266 int klist_node_attached(struct klist_node *n)
 267 {
 268         return (n->n_klist != NULL);
 269 }
 270 EXPORT_SYMBOL_GPL(klist_node_attached);
 271
 272 /**
 273  * klist_iter_init_node - Initialize a klist_iter structure.
 274  * @k: klist we're iterating.
 275  * @i: klist_iter we're filling.
 276  * @n: node to start with.
 277  *
 278  * Similar to klist_iter_init(), but starts the action off with @n,
 279  * instead of with the list head.
 280  */
 281 void klist_iter_init_node(struct klist *k, struct klist_iter *i,
 282                           struct klist_node *n)
 283 {
 284         i->i_klist = k;
 285         i->i_cur = n;
 286         if (n)
 287                 kref_get(&n->n_ref);
 288 }
 289 EXPORT_SYMBOL_GPL(klist_iter_init_node);
 290
 291 /**
 292  * klist_iter_init - Iniitalize a klist_iter structure.
 293  * @k: klist we're iterating.
 294  * @i: klist_iter structure we're filling.
 295  *
 296  * Similar to klist_iter_init_node(), but start with the list head.
 297  */
 298 void klist_iter_init(struct klist *k, struct klist_iter *i)
 299 {
 300         klist_iter_init_node(k, i, NULL);
 301 }
 302 EXPORT_SYMBOL_GPL(klist_iter_init);
 303
 304 /**
 305  * klist_iter_exit - Finish a list iteration.
 306  * @i: Iterator structure.
 307  *
 308  * Must be called when done iterating over list, as it decrements the
 309  * refcount of the current node. Necessary in case iteration exited before
 310  * the end of the list was reached, and always good form.
 311  */
 312 void klist_iter_exit(struct klist_iter *i)
 313 {
 314         if (i->i_cur) {
 315                 klist_put(i->i_cur, false);
 316                 i->i_cur = NULL;
 317         }
 318 }
 319 EXPORT_SYMBOL_GPL(klist_iter_exit);
 320
 321 static struct klist_node *to_klist_node(struct list_head *n)
 322 {
 323         return container_of(n, struct klist_node, n_node);
 324 }
 325
 326 /**
 327  * klist_next - Ante up next node in list.
 328  * @i: Iterator structure.
 329  *
 330  * First grab list lock. Decrement the reference count of the previous
 331  * node, if there was one. Grab the next node, increment its reference
 332  * count, drop the lock, and return that next node.
 333  */
 334 struct klist_node *klist_next(struct klist_iter *i)
 335 {
 336         void (*put)(struct klist_node *) = i->i_klist->put;
 337         struct klist_node *last = i->i_cur;
 338         struct klist_node *next;
 339
 340         spin_lock(&i->i_klist->k_lock);
 341
 342         if (last) {
 343                 next = to_klist_node(last->n_node.next);
 344                 if (!klist_dec_and_del(last))
 345                         put = NULL;
 346         } else
 347                 next = to_klist_node(i->i_klist->k_list.next);
 348
 349         i->i_cur = NULL;
 350         while (next != to_klist_node(&i->i_klist->k_list)) {
 351                 if (likely(!knode_dead(next))) {
 352                         kref_get(&next->n_ref);
 353                         i->i_cur = next;
 354                         break;
 355                 }
 356                 next = to_klist_node(next->n_node.next);
 357         }
 358
 359         spin_unlock(&i->i_klist->k_lock);
 360
 361         if (put && last)
 362                 put(last);
 363         return i->i_cur;
 364 }
 365 EXPORT_SYMBOL_GPL(klist_next);