linux/lib/idr.c
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   1/*
   2 * 2002-10-18  written by Jim Houston jim.houston@ccur.com
   3 *      Copyright (C) 2002 by Concurrent Computer Corporation
   4 *      Distributed under the GNU GPL license version 2.
   5 *
   6 * Modified by George Anzinger to reuse immediately and to use
   7 * find bit instructions.  Also removed _irq on spinlocks.
   8 *
   9 * Modified by Nadia Derbey to make it RCU safe.
  10 *
  11 * Small id to pointer translation service.
  12 *
  13 * It uses a radix tree like structure as a sparse array indexed
  14 * by the id to obtain the pointer.  The bitmap makes allocating
  15 * a new id quick.
  16 *
  17 * You call it to allocate an id (an int) an associate with that id a
  18 * pointer or what ever, we treat it as a (void *).  You can pass this
  19 * id to a user for him to pass back at a later time.  You then pass
  20 * that id to this code and it returns your pointer.
  21
  22 * You can release ids at any time. When all ids are released, most of
  23 * the memory is returned (we keep MAX_IDR_FREE) in a local pool so we
  24 * don't need to go to the memory "store" during an id allocate, just
  25 * so you don't need to be too concerned about locking and conflicts
  26 * with the slab allocator.
  27 */
  28
  29#ifndef TEST                        // to test in user space...
  30#include <linux/slab.h>
  31#include <linux/init.h>
  32#include <linux/export.h>
  33#endif
  34#include <linux/err.h>
  35#include <linux/string.h>
  36#include <linux/idr.h>
  37#include <linux/spinlock.h>
  38#include <linux/percpu.h>
  39#include <linux/hardirq.h>
  40
  41#define MAX_IDR_SHIFT           (sizeof(int) * 8 - 1)
  42#define MAX_IDR_BIT             (1U << MAX_IDR_SHIFT)
  43
  44/* Leave the possibility of an incomplete final layer */
  45#define MAX_IDR_LEVEL ((MAX_IDR_SHIFT + IDR_BITS - 1) / IDR_BITS)
  46
  47/* Number of id_layer structs to leave in free list */
  48#define MAX_IDR_FREE (MAX_IDR_LEVEL * 2)
  49
  50static struct kmem_cache *idr_layer_cache;
  51static DEFINE_PER_CPU(struct idr_layer *, idr_preload_head);
  52static DEFINE_PER_CPU(int, idr_preload_cnt);
  53static DEFINE_SPINLOCK(simple_ida_lock);
  54
  55/* the maximum ID which can be allocated given idr->layers */
  56static int idr_max(int layers)
  57{
  58        int bits = min_t(int, layers * IDR_BITS, MAX_IDR_SHIFT);
  59
  60        return (1 << bits) - 1;
  61}
  62
  63/*
  64 * Prefix mask for an idr_layer at @layer.  For layer 0, the prefix mask is
  65 * all bits except for the lower IDR_BITS.  For layer 1, 2 * IDR_BITS, and
  66 * so on.
  67 */
  68static int idr_layer_prefix_mask(int layer)
  69{
  70        return ~idr_max(layer + 1);
  71}
  72
  73static struct idr_layer *get_from_free_list(struct idr *idp)
  74{
  75        struct idr_layer *p;
  76        unsigned long flags;
  77
  78        spin_lock_irqsave(&idp->lock, flags);
  79        if ((p = idp->id_free)) {
  80                idp->id_free = p->ary[0];
  81                idp->id_free_cnt--;
  82                p->ary[0] = NULL;
  83        }
  84        spin_unlock_irqrestore(&idp->lock, flags);
  85        return(p);
  86}
  87
  88/**
  89 * idr_layer_alloc - allocate a new idr_layer
  90 * @gfp_mask: allocation mask
  91 * @layer_idr: optional idr to allocate from
  92 *
  93 * If @layer_idr is %NULL, directly allocate one using @gfp_mask or fetch
  94 * one from the per-cpu preload buffer.  If @layer_idr is not %NULL, fetch
  95 * an idr_layer from @idr->id_free.
  96 *
  97 * @layer_idr is to maintain backward compatibility with the old alloc
  98 * interface - idr_pre_get() and idr_get_new*() - and will be removed
  99 * together with per-pool preload buffer.
 100 */
 101static struct idr_layer *idr_layer_alloc(gfp_t gfp_mask, struct idr *layer_idr)
 102{
 103        struct idr_layer *new;
 104
 105        /* this is the old path, bypass to get_from_free_list() */
 106        if (layer_idr)
 107                return get_from_free_list(layer_idr);
 108
 109        /*
 110         * Try to allocate directly from kmem_cache.  We want to try this
 111         * before preload buffer; otherwise, non-preloading idr_alloc()
 112         * users will end up taking advantage of preloading ones.  As the
 113         * following is allowed to fail for preloaded cases, suppress
 114         * warning this time.
 115         */
 116        new = kmem_cache_zalloc(idr_layer_cache, gfp_mask | __GFP_NOWARN);
 117        if (new)
 118                return new;
 119
 120        /*
 121         * Try to fetch one from the per-cpu preload buffer if in process
 122         * context.  See idr_preload() for details.
 123         */
 124        if (!in_interrupt()) {
 125                preempt_disable();
 126                new = __this_cpu_read(idr_preload_head);
 127                if (new) {
 128                        __this_cpu_write(idr_preload_head, new->ary[0]);
 129                        __this_cpu_dec(idr_preload_cnt);
 130                        new->ary[0] = NULL;
 131                }
 132                preempt_enable();
 133                if (new)
 134                        return new;
 135        }
 136
 137        /*
 138         * Both failed.  Try kmem_cache again w/o adding __GFP_NOWARN so
 139         * that memory allocation failure warning is printed as intended.
 140         */
 141        return kmem_cache_zalloc(idr_layer_cache, gfp_mask);
 142}
 143
 144static void idr_layer_rcu_free(struct rcu_head *head)
 145{
 146        struct idr_layer *layer;
 147
 148        layer = container_of(head, struct idr_layer, rcu_head);
 149        kmem_cache_free(idr_layer_cache, layer);
 150}
 151
 152static inline void free_layer(struct idr *idr, struct idr_layer *p)
 153{
 154        if (idr->hint && idr->hint == p)
 155                RCU_INIT_POINTER(idr->hint, NULL);
 156        call_rcu(&p->rcu_head, idr_layer_rcu_free);
 157}
 158
 159/* only called when idp->lock is held */
 160static void __move_to_free_list(struct idr *idp, struct idr_layer *p)
 161{
 162        p->ary[0] = idp->id_free;
 163        idp->id_free = p;
 164        idp->id_free_cnt++;
 165}
 166
 167static void move_to_free_list(struct idr *idp, struct idr_layer *p)
 168{
 169        unsigned long flags;
 170
 171        /*
 172         * Depends on the return element being zeroed.
 173         */
 174        spin_lock_irqsave(&idp->lock, flags);
 175        __move_to_free_list(idp, p);
 176        spin_unlock_irqrestore(&idp->lock, flags);
 177}
 178
 179static void idr_mark_full(struct idr_layer **pa, int id)
 180{
 181        struct idr_layer *p = pa[0];
 182        int l = 0;
 183
 184        __set_bit(id & IDR_MASK, p->bitmap);
 185        /*
 186         * If this layer is full mark the bit in the layer above to
 187         * show that this part of the radix tree is full.  This may
 188         * complete the layer above and require walking up the radix
 189         * tree.
 190         */
 191        while (bitmap_full(p->bitmap, IDR_SIZE)) {
 192                if (!(p = pa[++l]))
 193                        break;
 194                id = id >> IDR_BITS;
 195                __set_bit((id & IDR_MASK), p->bitmap);
 196        }
 197}
 198
 199int __idr_pre_get(struct idr *idp, gfp_t gfp_mask)
 200{
 201        while (idp->id_free_cnt < MAX_IDR_FREE) {
 202                struct idr_layer *new;
 203                new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
 204                if (new == NULL)
 205                        return (0);
 206                move_to_free_list(idp, new);
 207        }
 208        return 1;
 209}
 210EXPORT_SYMBOL(__idr_pre_get);
 211
 212/**
 213 * sub_alloc - try to allocate an id without growing the tree depth
 214 * @idp: idr handle
 215 * @starting_id: id to start search at
 216 * @pa: idr_layer[MAX_IDR_LEVEL] used as backtrack buffer
 217 * @gfp_mask: allocation mask for idr_layer_alloc()
 218 * @layer_idr: optional idr passed to idr_layer_alloc()
 219 *
 220 * Allocate an id in range [@starting_id, INT_MAX] from @idp without
 221 * growing its depth.  Returns
 222 *
 223 *  the allocated id >= 0 if successful,
 224 *  -EAGAIN if the tree needs to grow for allocation to succeed,
 225 *  -ENOSPC if the id space is exhausted,
 226 *  -ENOMEM if more idr_layers need to be allocated.
 227 */
 228static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa,
 229                     gfp_t gfp_mask, struct idr *layer_idr)
 230{
 231        int n, m, sh;
 232        struct idr_layer *p, *new;
 233        int l, id, oid;
 234
 235        id = *starting_id;
 236 restart:
 237        p = idp->top;
 238        l = idp->layers;
 239        pa[l--] = NULL;
 240        while (1) {
 241                /*
 242                 * We run around this while until we reach the leaf node...
 243                 */
 244                n = (id >> (IDR_BITS*l)) & IDR_MASK;
 245                m = find_next_zero_bit(p->bitmap, IDR_SIZE, n);
 246                if (m == IDR_SIZE) {
 247                        /* no space available go back to previous layer. */
 248                        l++;
 249                        oid = id;
 250                        id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;
 251
 252                        /* if already at the top layer, we need to grow */
 253                        if (id >= 1 << (idp->layers * IDR_BITS)) {
 254                                *starting_id = id;
 255                                return -EAGAIN;
 256                        }
 257                        p = pa[l];
 258                        BUG_ON(!p);
 259
 260                        /* If we need to go up one layer, continue the
 261                         * loop; otherwise, restart from the top.
 262                         */
 263                        sh = IDR_BITS * (l + 1);
 264                        if (oid >> sh == id >> sh)
 265                                continue;
 266                        else
 267                                goto restart;
 268                }
 269                if (m != n) {
 270                        sh = IDR_BITS*l;
 271                        id = ((id >> sh) ^ n ^ m) << sh;
 272                }
 273                if ((id >= MAX_IDR_BIT) || (id < 0))
 274                        return -ENOSPC;
 275                if (l == 0)
 276                        break;
 277                /*
 278                 * Create the layer below if it is missing.
 279                 */
 280                if (!p->ary[m]) {
 281                        new = idr_layer_alloc(gfp_mask, layer_idr);
 282                        if (!new)
 283                                return -ENOMEM;
 284                        new->layer = l-1;
 285                        new->prefix = id & idr_layer_prefix_mask(new->layer);
 286                        rcu_assign_pointer(p->ary[m], new);
 287                        p->count++;
 288                }
 289                pa[l--] = p;
 290                p = p->ary[m];
 291        }
 292
 293        pa[l] = p;
 294        return id;
 295}
 296
 297static int idr_get_empty_slot(struct idr *idp, int starting_id,
 298                              struct idr_layer **pa, gfp_t gfp_mask,
 299                              struct idr *layer_idr)
 300{
 301        struct idr_layer *p, *new;
 302        int layers, v, id;
 303        unsigned long flags;
 304
 305        id = starting_id;
 306build_up:
 307        p = idp->top;
 308        layers = idp->layers;
 309        if (unlikely(!p)) {
 310                if (!(p = idr_layer_alloc(gfp_mask, layer_idr)))
 311                        return -ENOMEM;
 312                p->layer = 0;
 313                layers = 1;
 314        }
 315        /*
 316         * Add a new layer to the top of the tree if the requested
 317         * id is larger than the currently allocated space.
 318         */
 319        while (id > idr_max(layers)) {
 320                layers++;
 321                if (!p->count) {
 322                        /* special case: if the tree is currently empty,
 323                         * then we grow the tree by moving the top node
 324                         * upwards.
 325                         */
 326                        p->layer++;
 327                        WARN_ON_ONCE(p->prefix);
 328                        continue;
 329                }
 330                if (!(new = idr_layer_alloc(gfp_mask, layer_idr))) {
 331                        /*
 332                         * The allocation failed.  If we built part of
 333                         * the structure tear it down.
 334                         */
 335                        spin_lock_irqsave(&idp->lock, flags);
 336                        for (new = p; p && p != idp->top; new = p) {
 337                                p = p->ary[0];
 338                                new->ary[0] = NULL;
 339                                new->count = 0;
 340                                bitmap_clear(new->bitmap, 0, IDR_SIZE);
 341                                __move_to_free_list(idp, new);
 342                        }
 343                        spin_unlock_irqrestore(&idp->lock, flags);
 344                        return -ENOMEM;
 345                }
 346                new->ary[0] = p;
 347                new->count = 1;
 348                new->layer = layers-1;
 349                new->prefix = id & idr_layer_prefix_mask(new->layer);
 350                if (bitmap_full(p->bitmap, IDR_SIZE))
 351                        __set_bit(0, new->bitmap);
 352                p = new;
 353        }
 354        rcu_assign_pointer(idp->top, p);
 355        idp->layers = layers;
 356        v = sub_alloc(idp, &id, pa, gfp_mask, layer_idr);
 357        if (v == -EAGAIN)
 358                goto build_up;
 359        return(v);
 360}
 361
 362/*
 363 * @id and @pa are from a successful allocation from idr_get_empty_slot().
 364 * Install the user pointer @ptr and mark the slot full.
 365 */
 366static void idr_fill_slot(struct idr *idr, void *ptr, int id,
 367                          struct idr_layer **pa)
 368{
 369        /* update hint used for lookup, cleared from free_layer() */
 370        rcu_assign_pointer(idr->hint, pa[0]);
 371
 372        rcu_assign_pointer(pa[0]->ary[id & IDR_MASK], (struct idr_layer *)ptr);
 373        pa[0]->count++;
 374        idr_mark_full(pa, id);
 375}
 376
 377int __idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
 378{
 379        struct idr_layer *pa[MAX_IDR_LEVEL + 1];
 380        int rv;
 381
 382        rv = idr_get_empty_slot(idp, starting_id, pa, 0, idp);
 383        if (rv < 0)
 384                return rv == -ENOMEM ? -EAGAIN : rv;
 385
 386        idr_fill_slot(idp, ptr, rv, pa);
 387        *id = rv;
 388        return 0;
 389}
 390EXPORT_SYMBOL(__idr_get_new_above);
 391
 392/**
 393 * idr_preload - preload for idr_alloc()
 394 * @gfp_mask: allocation mask to use for preloading
 395 *
 396 * Preload per-cpu layer buffer for idr_alloc().  Can only be used from
 397 * process context and each idr_preload() invocation should be matched with
 398 * idr_preload_end().  Note that preemption is disabled while preloaded.
 399 *
 400 * The first idr_alloc() in the preloaded section can be treated as if it
 401 * were invoked with @gfp_mask used for preloading.  This allows using more
 402 * permissive allocation masks for idrs protected by spinlocks.
 403 *
 404 * For example, if idr_alloc() below fails, the failure can be treated as
 405 * if idr_alloc() were called with GFP_KERNEL rather than GFP_NOWAIT.
 406 *
 407 *      idr_preload(GFP_KERNEL);
 408 *      spin_lock(lock);
 409 *
 410 *      id = idr_alloc(idr, ptr, start, end, GFP_NOWAIT);
 411 *
 412 *      spin_unlock(lock);
 413 *      idr_preload_end();
 414 *      if (id < 0)
 415 *              error;
 416 */
 417void idr_preload(gfp_t gfp_mask)
 418{
 419        /*
 420         * Consuming preload buffer from non-process context breaks preload
 421         * allocation guarantee.  Disallow usage from those contexts.
 422         */
 423        WARN_ON_ONCE(in_interrupt());
 424        might_sleep_if(gfp_mask & __GFP_WAIT);
 425
 426        preempt_disable();
 427
 428        /*
 429         * idr_alloc() is likely to succeed w/o full idr_layer buffer and
 430         * return value from idr_alloc() needs to be checked for failure
 431         * anyway.  Silently give up if allocation fails.  The caller can
 432         * treat failures from idr_alloc() as if idr_alloc() were called
 433         * with @gfp_mask which should be enough.
 434         */
 435        while (__this_cpu_read(idr_preload_cnt) < MAX_IDR_FREE) {
 436                struct idr_layer *new;
 437
 438                preempt_enable();
 439                new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
 440                preempt_disable();
 441                if (!new)
 442                        break;
 443
 444                /* link the new one to per-cpu preload list */
 445                new->ary[0] = __this_cpu_read(idr_preload_head);
 446                __this_cpu_write(idr_preload_head, new);
 447                __this_cpu_inc(idr_preload_cnt);
 448        }
 449}
 450EXPORT_SYMBOL(idr_preload);
 451
 452/**
 453 * idr_alloc - allocate new idr entry
 454 * @idr: the (initialized) idr
 455 * @ptr: pointer to be associated with the new id
 456 * @start: the minimum id (inclusive)
 457 * @end: the maximum id (exclusive, <= 0 for max)
 458 * @gfp_mask: memory allocation flags
 459 *
 460 * Allocate an id in [start, end) and associate it with @ptr.  If no ID is
 461 * available in the specified range, returns -ENOSPC.  On memory allocation
 462 * failure, returns -ENOMEM.
 463 *
 464 * Note that @end is treated as max when <= 0.  This is to always allow
 465 * using @start + N as @end as long as N is inside integer range.
 466 *
 467 * The user is responsible for exclusively synchronizing all operations
 468 * which may modify @idr.  However, read-only accesses such as idr_find()
 469 * or iteration can be performed under RCU read lock provided the user
 470 * destroys @ptr in RCU-safe way after removal from idr.
 471 */
 472int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask)
 473{
 474        int max = end > 0 ? end - 1 : INT_MAX;  /* inclusive upper limit */
 475        struct idr_layer *pa[MAX_IDR_LEVEL + 1];
 476        int id;
 477
 478        might_sleep_if(gfp_mask & __GFP_WAIT);
 479
 480        /* sanity checks */
 481        if (WARN_ON_ONCE(start < 0))
 482                return -EINVAL;
 483        if (unlikely(max < start))
 484                return -ENOSPC;
 485
 486        /* allocate id */
 487        id = idr_get_empty_slot(idr, start, pa, gfp_mask, NULL);
 488        if (unlikely(id < 0))
 489                return id;
 490        if (unlikely(id > max))
 491                return -ENOSPC;
 492
 493        idr_fill_slot(idr, ptr, id, pa);
 494        return id;
 495}
 496EXPORT_SYMBOL_GPL(idr_alloc);
 497
 498/**
 499 * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
 500 * @idr: the (initialized) idr
 501 * @ptr: pointer to be associated with the new id
 502 * @start: the minimum id (inclusive)
 503 * @end: the maximum id (exclusive, <= 0 for max)
 504 * @gfp_mask: memory allocation flags
 505 *
 506 * Essentially the same as idr_alloc, but prefers to allocate progressively
 507 * higher ids if it can. If the "cur" counter wraps, then it will start again
 508 * at the "start" end of the range and allocate one that has already been used.
 509 */
 510int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end,
 511                        gfp_t gfp_mask)
 512{
 513        int id;
 514
 515        id = idr_alloc(idr, ptr, max(start, idr->cur), end, gfp_mask);
 516        if (id == -ENOSPC)
 517                id = idr_alloc(idr, ptr, start, end, gfp_mask);
 518
 519        if (likely(id >= 0))
 520                idr->cur = id + 1;
 521        return id;
 522}
 523EXPORT_SYMBOL(idr_alloc_cyclic);
 524
 525static void idr_remove_warning(int id)
 526{
 527        printk(KERN_WARNING
 528                "idr_remove called for id=%d which is not allocated.\n", id);
 529        dump_stack();
 530}
 531
 532static void sub_remove(struct idr *idp, int shift, int id)
 533{
 534        struct idr_layer *p = idp->top;
 535        struct idr_layer **pa[MAX_IDR_LEVEL + 1];
 536        struct idr_layer ***paa = &pa[0];
 537        struct idr_layer *to_free;
 538        int n;
 539
 540        *paa = NULL;
 541        *++paa = &idp->top;
 542
 543        while ((shift > 0) && p) {
 544                n = (id >> shift) & IDR_MASK;
 545                __clear_bit(n, p->bitmap);
 546                *++paa = &p->ary[n];
 547                p = p->ary[n];
 548                shift -= IDR_BITS;
 549        }
 550        n = id & IDR_MASK;
 551        if (likely(p != NULL && test_bit(n, p->bitmap))) {
 552                __clear_bit(n, p->bitmap);
 553                rcu_assign_pointer(p->ary[n], NULL);
 554                to_free = NULL;
 555                while(*paa && ! --((**paa)->count)){
 556                        if (to_free)
 557                                free_layer(idp, to_free);
 558                        to_free = **paa;
 559                        **paa-- = NULL;
 560                }
 561                if (!*paa)
 562                        idp->layers = 0;
 563                if (to_free)
 564                        free_layer(idp, to_free);
 565        } else
 566                idr_remove_warning(id);
 567}
 568
 569/**
 570 * idr_remove - remove the given id and free its slot
 571 * @idp: idr handle
 572 * @id: unique key
 573 */
 574void idr_remove(struct idr *idp, int id)
 575{
 576        struct idr_layer *p;
 577        struct idr_layer *to_free;
 578
 579        if (id < 0)
 580                return;
 581
 582        sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
 583        if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
 584            idp->top->ary[0]) {
 585                /*
 586                 * Single child at leftmost slot: we can shrink the tree.
 587                 * This level is not needed anymore since when layers are
 588                 * inserted, they are inserted at the top of the existing
 589                 * tree.
 590                 */
 591                to_free = idp->top;
 592                p = idp->top->ary[0];
 593                rcu_assign_pointer(idp->top, p);
 594                --idp->layers;
 595                to_free->count = 0;
 596                bitmap_clear(to_free->bitmap, 0, IDR_SIZE);
 597                free_layer(idp, to_free);
 598        }
 599        while (idp->id_free_cnt >= MAX_IDR_FREE) {
 600                p = get_from_free_list(idp);
 601                /*
 602                 * Note: we don't call the rcu callback here, since the only
 603                 * layers that fall into the freelist are those that have been
 604                 * preallocated.
 605                 */
 606                kmem_cache_free(idr_layer_cache, p);
 607        }
 608        return;
 609}
 610EXPORT_SYMBOL(idr_remove);
 611
 612void __idr_remove_all(struct idr *idp)
 613{
 614        int n, id, max;
 615        int bt_mask;
 616        struct idr_layer *p;
 617        struct idr_layer *pa[MAX_IDR_LEVEL + 1];
 618        struct idr_layer **paa = &pa[0];
 619
 620        n = idp->layers * IDR_BITS;
 621        p = idp->top;
 622        rcu_assign_pointer(idp->top, NULL);
 623        max = idr_max(idp->layers);
 624
 625        id = 0;
 626        while (id >= 0 && id <= max) {
 627                while (n > IDR_BITS && p) {
 628                        n -= IDR_BITS;
 629                        *paa++ = p;
 630                        p = p->ary[(id >> n) & IDR_MASK];
 631                }
 632
 633                bt_mask = id;
 634                id += 1 << n;
 635                /* Get the highest bit that the above add changed from 0->1. */
 636                while (n < fls(id ^ bt_mask)) {
 637                        if (p)
 638                                free_layer(idp, p);
 639                        n += IDR_BITS;
 640                        p = *--paa;
 641                }
 642        }
 643        idp->layers = 0;
 644}
 645EXPORT_SYMBOL(__idr_remove_all);
 646
 647/**
 648 * idr_destroy - release all cached layers within an idr tree
 649 * @idp: idr handle
 650 *
 651 * Free all id mappings and all idp_layers.  After this function, @idp is
 652 * completely unused and can be freed / recycled.  The caller is
 653 * responsible for ensuring that no one else accesses @idp during or after
 654 * idr_destroy().
 655 *
 656 * A typical clean-up sequence for objects stored in an idr tree will use
 657 * idr_for_each() to free all objects, if necessay, then idr_destroy() to
 658 * free up the id mappings and cached idr_layers.
 659 */
 660void idr_destroy(struct idr *idp)
 661{
 662        __idr_remove_all(idp);
 663
 664        while (idp->id_free_cnt) {
 665                struct idr_layer *p = get_from_free_list(idp);
 666                kmem_cache_free(idr_layer_cache, p);
 667        }
 668}
 669EXPORT_SYMBOL(idr_destroy);
 670
 671void *idr_find_slowpath(struct idr *idp, int id)
 672{
 673        int n;
 674        struct idr_layer *p;
 675
 676        if (id < 0)
 677                return NULL;
 678
 679        p = rcu_dereference_raw(idp->top);
 680        if (!p)
 681                return NULL;
 682        n = (p->layer+1) * IDR_BITS;
 683
 684        if (id > idr_max(p->layer + 1))
 685                return NULL;
 686        BUG_ON(n == 0);
 687
 688        while (n > 0 && p) {
 689                n -= IDR_BITS;
 690                BUG_ON(n != p->layer*IDR_BITS);
 691                p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);
 692        }
 693        return((void *)p);
 694}
 695EXPORT_SYMBOL(idr_find_slowpath);
 696
 697/**
 698 * idr_for_each - iterate through all stored pointers
 699 * @idp: idr handle
 700 * @fn: function to be called for each pointer
 701 * @data: data passed back to callback function
 702 *
 703 * Iterate over the pointers registered with the given idr.  The
 704 * callback function will be called for each pointer currently
 705 * registered, passing the id, the pointer and the data pointer passed
 706 * to this function.  It is not safe to modify the idr tree while in
 707 * the callback, so functions such as idr_get_new and idr_remove are
 708 * not allowed.
 709 *
 710 * We check the return of @fn each time. If it returns anything other
 711 * than %0, we break out and return that value.
 712 *
 713 * The caller must serialize idr_for_each() vs idr_get_new() and idr_remove().
 714 */
 715int idr_for_each(struct idr *idp,
 716                 int (*fn)(int id, void *p, void *data), void *data)
 717{
 718        int n, id, max, error = 0;
 719        struct idr_layer *p;
 720        struct idr_layer *pa[MAX_IDR_LEVEL + 1];
 721        struct idr_layer **paa = &pa[0];
 722
 723        n = idp->layers * IDR_BITS;
 724        p = rcu_dereference_raw(idp->top);
 725        max = idr_max(idp->layers);
 726
 727        id = 0;
 728        while (id >= 0 && id <= max) {
 729                while (n > 0 && p) {
 730                        n -= IDR_BITS;
 731                        *paa++ = p;
 732                        p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);
 733                }
 734
 735                if (p) {
 736                        error = fn(id, (void *)p, data);
 737                        if (error)
 738                                break;
 739                }
 740
 741                id += 1 << n;
 742                while (n < fls(id)) {
 743                        n += IDR_BITS;
 744                        p = *--paa;
 745                }
 746        }
 747
 748        return error;
 749}
 750EXPORT_SYMBOL(idr_for_each);
 751
 752/**
 753 * idr_get_next - lookup next object of id to given id.
 754 * @idp: idr handle
 755 * @nextidp:  pointer to lookup key
 756 *
 757 * Returns pointer to registered object with id, which is next number to
 758 * given id. After being looked up, *@nextidp will be updated for the next
 759 * iteration.
 760 *
 761 * This function can be called under rcu_read_lock(), given that the leaf
 762 * pointers lifetimes are correctly managed.
 763 */
 764void *idr_get_next(struct idr *idp, int *nextidp)
 765{
 766        struct idr_layer *p, *pa[MAX_IDR_LEVEL + 1];
 767        struct idr_layer **paa = &pa[0];
 768        int id = *nextidp;
 769        int n, max;
 770
 771        /* find first ent */
 772        p = rcu_dereference_raw(idp->top);
 773        if (!p)
 774                return NULL;
 775        n = (p->layer + 1) * IDR_BITS;
 776        max = idr_max(p->layer + 1);
 777
 778        while (id >= 0 && id <= max) {
 779                while (n > 0 && p) {
 780                        n -= IDR_BITS;
 781                        *paa++ = p;
 782                        p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);
 783                }
 784
 785                if (p) {
 786                        *nextidp = id;
 787                        return p;
 788                }
 789
 790                /*
 791                 * Proceed to the next layer at the current level.  Unlike
 792                 * idr_for_each(), @id isn't guaranteed to be aligned to
 793                 * layer boundary at this point and adding 1 << n may
 794                 * incorrectly skip IDs.  Make sure we jump to the
 795                 * beginning of the next layer using round_up().
 796                 */
 797                id = round_up(id + 1, 1 << n);
 798                while (n < fls(id)) {
 799                        n += IDR_BITS;
 800                        p = *--paa;
 801                }
 802        }
 803        return NULL;
 804}
 805EXPORT_SYMBOL(idr_get_next);
 806
 807
 808/**
 809 * idr_replace - replace pointer for given id
 810 * @idp: idr handle
 811 * @ptr: pointer you want associated with the id
 812 * @id: lookup key
 813 *
 814 * Replace the pointer registered with an id and return the old value.
 815 * A %-ENOENT return indicates that @id was not found.
 816 * A %-EINVAL return indicates that @id was not within valid constraints.
 817 *
 818 * The caller must serialize with writers.
 819 */
 820void *idr_replace(struct idr *idp, void *ptr, int id)
 821{
 822        int n;
 823        struct idr_layer *p, *old_p;
 824
 825        if (id < 0)
 826                return ERR_PTR(-EINVAL);
 827
 828        p = idp->top;
 829        if (!p)
 830                return ERR_PTR(-EINVAL);
 831
 832        n = (p->layer+1) * IDR_BITS;
 833
 834        if (id >= (1 << n))
 835                return ERR_PTR(-EINVAL);
 836
 837        n -= IDR_BITS;
 838        while ((n > 0) && p) {
 839                p = p->ary[(id >> n) & IDR_MASK];
 840                n -= IDR_BITS;
 841        }
 842
 843        n = id & IDR_MASK;
 844        if (unlikely(p == NULL || !test_bit(n, p->bitmap)))
 845                return ERR_PTR(-ENOENT);
 846
 847        old_p = p->ary[n];
 848        rcu_assign_pointer(p->ary[n], ptr);
 849
 850        return old_p;
 851}
 852EXPORT_SYMBOL(idr_replace);
 853
 854void __init idr_init_cache(void)
 855{
 856        idr_layer_cache = kmem_cache_create("idr_layer_cache",
 857                                sizeof(struct idr_layer), 0, SLAB_PANIC, NULL);
 858}
 859
 860/**
 861 * idr_init - initialize idr handle
 862 * @idp:        idr handle
 863 *
 864 * This function is use to set up the handle (@idp) that you will pass
 865 * to the rest of the functions.
 866 */
 867void idr_init(struct idr *idp)
 868{
 869        memset(idp, 0, sizeof(struct idr));
 870        spin_lock_init(&idp->lock);
 871}
 872EXPORT_SYMBOL(idr_init);
 873
 874
 875/**
 876 * DOC: IDA description
 877 * IDA - IDR based ID allocator
 878 *
 879 * This is id allocator without id -> pointer translation.  Memory
 880 * usage is much lower than full blown idr because each id only
 881 * occupies a bit.  ida uses a custom leaf node which contains
 882 * IDA_BITMAP_BITS slots.
 883 *
 884 * 2007-04-25  written by Tejun Heo <htejun@gmail.com>
 885 */
 886
 887static void free_bitmap(struct ida *ida, struct ida_bitmap *bitmap)
 888{
 889        unsigned long flags;
 890
 891        if (!ida->free_bitmap) {
 892                spin_lock_irqsave(&ida->idr.lock, flags);
 893                if (!ida->free_bitmap) {
 894                        ida->free_bitmap = bitmap;
 895                        bitmap = NULL;
 896                }
 897                spin_unlock_irqrestore(&ida->idr.lock, flags);
 898        }
 899
 900        kfree(bitmap);
 901}
 902
 903/**
 904 * ida_pre_get - reserve resources for ida allocation
 905 * @ida:        ida handle
 906 * @gfp_mask:   memory allocation flag
 907 *
 908 * This function should be called prior to locking and calling the
 909 * following function.  It preallocates enough memory to satisfy the
 910 * worst possible allocation.
 911 *
 912 * If the system is REALLY out of memory this function returns %0,
 913 * otherwise %1.
 914 */
 915int ida_pre_get(struct ida *ida, gfp_t gfp_mask)
 916{
 917        /* allocate idr_layers */
 918        if (!__idr_pre_get(&ida->idr, gfp_mask))
 919                return 0;
 920
 921        /* allocate free_bitmap */
 922        if (!ida->free_bitmap) {
 923                struct ida_bitmap *bitmap;
 924
 925                bitmap = kmalloc(sizeof(struct ida_bitmap), gfp_mask);
 926                if (!bitmap)
 927                        return 0;
 928
 929                free_bitmap(ida, bitmap);
 930        }
 931
 932        return 1;
 933}
 934EXPORT_SYMBOL(ida_pre_get);
 935
 936/**
 937 * ida_get_new_above - allocate new ID above or equal to a start id
 938 * @ida:        ida handle
 939 * @starting_id: id to start search at
 940 * @p_id:       pointer to the allocated handle
 941 *
 942 * Allocate new ID above or equal to @starting_id.  It should be called
 943 * with any required locks.
 944 *
 945 * If memory is required, it will return %-EAGAIN, you should unlock
 946 * and go back to the ida_pre_get() call.  If the ida is full, it will
 947 * return %-ENOSPC.
 948 *
 949 * @p_id returns a value in the range @starting_id ... %0x7fffffff.
 950 */
 951int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
 952{
 953        struct idr_layer *pa[MAX_IDR_LEVEL + 1];
 954        struct ida_bitmap *bitmap;
 955        unsigned long flags;
 956        int idr_id = starting_id / IDA_BITMAP_BITS;
 957        int offset = starting_id % IDA_BITMAP_BITS;
 958        int t, id;
 959
 960 restart:
 961        /* get vacant slot */
 962        t = idr_get_empty_slot(&ida->idr, idr_id, pa, 0, &ida->idr);
 963        if (t < 0)
 964                return t == -ENOMEM ? -EAGAIN : t;
 965
 966        if (t * IDA_BITMAP_BITS >= MAX_IDR_BIT)
 967                return -ENOSPC;
 968
 969        if (t != idr_id)
 970                offset = 0;
 971        idr_id = t;
 972
 973        /* if bitmap isn't there, create a new one */
 974        bitmap = (void *)pa[0]->ary[idr_id & IDR_MASK];
 975        if (!bitmap) {
 976                spin_lock_irqsave(&ida->idr.lock, flags);
 977                bitmap = ida->free_bitmap;
 978                ida->free_bitmap = NULL;
 979                spin_unlock_irqrestore(&ida->idr.lock, flags);
 980
 981                if (!bitmap)
 982                        return -EAGAIN;
 983
 984                memset(bitmap, 0, sizeof(struct ida_bitmap));
 985                rcu_assign_pointer(pa[0]->ary[idr_id & IDR_MASK],
 986                                (void *)bitmap);
 987                pa[0]->count++;
 988        }
 989
 990        /* lookup for empty slot */
 991        t = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, offset);
 992        if (t == IDA_BITMAP_BITS) {
 993                /* no empty slot after offset, continue to the next chunk */
 994                idr_id++;
 995                offset = 0;
 996                goto restart;
 997        }
 998
 999        id = idr_id * IDA_BITMAP_BITS + t;
1000        if (id >= MAX_IDR_BIT)
1001                return -ENOSPC;
1002
1003        __set_bit(t, bitmap->bitmap);
1004        if (++bitmap->nr_busy == IDA_BITMAP_BITS)
1005                idr_mark_full(pa, idr_id);
1006
1007        *p_id = id;
1008
1009        /* Each leaf node can handle nearly a thousand slots and the
1010         * whole idea of ida is to have small memory foot print.
1011         * Throw away extra resources one by one after each successful
1012         * allocation.
1013         */
1014        if (ida->idr.id_free_cnt || ida->free_bitmap) {
1015                struct idr_layer *p = get_from_free_list(&ida->idr);
1016                if (p)
1017                        kmem_cache_free(idr_layer_cache, p);
1018        }
1019
1020        return 0;
1021}
1022EXPORT_SYMBOL(ida_get_new_above);
1023
1024/**
1025 * ida_remove - remove the given ID
1026 * @ida:        ida handle
1027 * @id:         ID to free
1028 */
1029void ida_remove(struct ida *ida, int id)
1030{
1031        struct idr_layer *p = ida->idr.top;
1032        int shift = (ida->idr.layers - 1) * IDR_BITS;
1033        int idr_id = id / IDA_BITMAP_BITS;
1034        int offset = id % IDA_BITMAP_BITS;
1035        int n;
1036        struct ida_bitmap *bitmap;
1037
1038        /* clear full bits while looking up the leaf idr_layer */
1039        while ((shift > 0) && p) {
1040                n = (idr_id >> shift) & IDR_MASK;
1041                __clear_bit(n, p->bitmap);
1042                p = p->ary[n];
1043                shift -= IDR_BITS;
1044        }
1045
1046        if (p == NULL)
1047                goto err;
1048
1049        n = idr_id & IDR_MASK;
1050        __clear_bit(n, p->bitmap);
1051
1052        bitmap = (void *)p->ary[n];
1053        if (!test_bit(offset, bitmap->bitmap))
1054                goto err;
1055
1056        /* update bitmap and remove it if empty */
1057        __clear_bit(offset, bitmap->bitmap);
1058        if (--bitmap->nr_busy == 0) {
1059                __set_bit(n, p->bitmap);        /* to please idr_remove() */
1060                idr_remove(&ida->idr, idr_id);
1061                free_bitmap(ida, bitmap);
1062        }
1063
1064        return;
1065
1066 err:
1067        printk(KERN_WARNING
1068               "ida_remove called for id=%d which is not allocated.\n", id);
1069}
1070EXPORT_SYMBOL(ida_remove);
1071
1072/**
1073 * ida_destroy - release all cached layers within an ida tree
1074 * @ida:                ida handle
1075 */
1076void ida_destroy(struct ida *ida)
1077{
1078        idr_destroy(&ida->idr);
1079        kfree(ida->free_bitmap);
1080}
1081EXPORT_SYMBOL(ida_destroy);
1082
1083/**
1084 * ida_simple_get - get a new id.
1085 * @ida: the (initialized) ida.
1086 * @start: the minimum id (inclusive, < 0x8000000)
1087 * @end: the maximum id (exclusive, < 0x8000000 or 0)
1088 * @gfp_mask: memory allocation flags
1089 *
1090 * Allocates an id in the range start <= id < end, or returns -ENOSPC.
1091 * On memory allocation failure, returns -ENOMEM.
1092 *
1093 * Use ida_simple_remove() to get rid of an id.
1094 */
1095int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
1096                   gfp_t gfp_mask)
1097{
1098        int ret, id;
1099        unsigned int max;
1100        unsigned long flags;
1101
1102        BUG_ON((int)start < 0);
1103        BUG_ON((int)end < 0);
1104
1105        if (end == 0)
1106                max = 0x80000000;
1107        else {
1108                BUG_ON(end < start);
1109                max = end - 1;
1110        }
1111
1112again:
1113        if (!ida_pre_get(ida, gfp_mask))
1114                return -ENOMEM;
1115
1116        spin_lock_irqsave(&simple_ida_lock, flags);
1117        ret = ida_get_new_above(ida, start, &id);
1118        if (!ret) {
1119                if (id > max) {
1120                        ida_remove(ida, id);
1121                        ret = -ENOSPC;
1122                } else {
1123                        ret = id;
1124                }
1125        }
1126        spin_unlock_irqrestore(&simple_ida_lock, flags);
1127
1128        if (unlikely(ret == -EAGAIN))
1129                goto again;
1130
1131        return ret;
1132}
1133EXPORT_SYMBOL(ida_simple_get);
1134
1135/**
1136 * ida_simple_remove - remove an allocated id.
1137 * @ida: the (initialized) ida.
1138 * @id: the id returned by ida_simple_get.
1139 */
1140void ida_simple_remove(struct ida *ida, unsigned int id)
1141{
1142        unsigned long flags;
1143
1144        BUG_ON((int)id < 0);
1145        spin_lock_irqsave(&simple_ida_lock, flags);
1146        ida_remove(ida, id);
1147        spin_unlock_irqrestore(&simple_ida_lock, flags);
1148}
1149EXPORT_SYMBOL(ida_simple_remove);
1150
1151/**
1152 * ida_init - initialize ida handle
1153 * @ida:        ida handle
1154 *
1155 * This function is use to set up the handle (@ida) that you will pass
1156 * to the rest of the functions.
1157 */
1158void ida_init(struct ida *ida)
1159{
1160        memset(ida, 0, sizeof(struct ida));
1161        idr_init(&ida->idr);
1162
1163}
1164EXPORT_SYMBOL(ida_init);
1165
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