linux/lib/klist.c
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   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
  48static struct klist *knode_klist(struct klist_node *knode)
  49{
  50        return (struct klist *)
  51                ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
  52}
  53
  54static bool knode_dead(struct klist_node *knode)
  55{
  56        return (unsigned long)knode->n_klist & KNODE_DEAD;
  57}
  58
  59static 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
  66static 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 */
  85void 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}
  93EXPORT_SYMBOL_GPL(klist_init);
  94
  95static 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
 102static 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
 109static 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 */
 123void klist_add_head(struct klist_node *n, struct klist *k)
 124{
 125        klist_node_init(k, n);
 126        add_head(k, n);
 127}
 128EXPORT_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 */
 135void klist_add_tail(struct klist_node *n, struct klist *k)
 136{
 137        klist_node_init(k, n);
 138        add_tail(k, n);
 139}
 140EXPORT_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 */
 147void 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}
 156EXPORT_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 */
 163void 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}
 172EXPORT_SYMBOL_GPL(klist_add_before);
 173
 174struct klist_waiter {
 175        struct list_head list;
 176        struct klist_node *node;
 177        struct task_struct *process;
 178        int woken;
 179};
 180
 181static DEFINE_SPINLOCK(klist_remove_lock);
 182static LIST_HEAD(klist_remove_waiters);
 183
 184static 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
 205static int klist_dec_and_del(struct klist_node *n)
 206{
 207        return kref_put(&n->n_ref, klist_release);
 208}
 209
 210static 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 */
 229void klist_del(struct klist_node *n)
 230{
 231        klist_put(n, true);
 232}
 233EXPORT_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 */
 239void 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}
 260EXPORT_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 */
 266int klist_node_attached(struct klist_node *n)
 267{
 268        return (n->n_klist != NULL);
 269}
 270EXPORT_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 */
 281void 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}
 289EXPORT_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 */
 298void klist_iter_init(struct klist *k, struct klist_iter *i)
 299{
 300        klist_iter_init_node(k, i, NULL);
 301}
 302EXPORT_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 */
 312void 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}
 319EXPORT_SYMBOL_GPL(klist_iter_exit);
 320
 321static 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 */
 334struct 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}
 365EXPORT_SYMBOL_GPL(klist_next);
 366
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