lib/idr.c

   1 #include <linux/bitmap.h>
   2 #include <linux/export.h>
   3 #include <linux/idr.h>
   4 #include <linux/slab.h>
   5 #include <linux/spinlock.h>
   6
   7 DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);
   8 static DEFINE_SPINLOCK(simple_ida_lock);
   9
  10 int idr_alloc_cmn(struct idr *idr, void *ptr, unsigned long *index,
  11                   unsigned long start, unsigned long end, gfp_t gfp,
  12                   bool ext)
  13 {
  14         struct radix_tree_iter iter;
  15         void __rcu **slot;
  16
  17         if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
  18                 return -EINVAL;
  19
  20         radix_tree_iter_init(&iter, start);
  21         if (ext)
  22                 slot = idr_get_free_ext(&idr->idr_rt, &iter, gfp, end);
  23         else
  24                 slot = idr_get_free(&idr->idr_rt, &iter, gfp, end);
  25         if (IS_ERR(slot))
  26                 return PTR_ERR(slot);
  27
  28         radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
  29         radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);
  30
  31         if (index)
  32                 *index = iter.index;
  33         return 0;
  34 }
  35 EXPORT_SYMBOL_GPL(idr_alloc_cmn);
  36
  37 /**
  38  * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
  39  * @idr: idr handle
  40  * @ptr: pointer to be associated with the new id
  41  * @start: the minimum id (inclusive)
  42  * @end: the maximum id (exclusive)
  43  * @gfp: memory allocation flags
  44  *
  45  * Allocates an ID larger than the last ID allocated if one is available.
  46  * If not, it will attempt to allocate the smallest ID that is larger or
  47  * equal to @start.
  48  */
  49 int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
  50 {
  51         int id, curr = idr->idr_next;
  52
  53         if (curr < start)
  54                 curr = start;
  55
  56         id = idr_alloc(idr, ptr, curr, end, gfp);
  57         if ((id == -ENOSPC) && (curr > start))
  58                 id = idr_alloc(idr, ptr, start, curr, gfp);
  59
  60         if (id >= 0)
  61                 idr->idr_next = id + 1U;
  62
  63         return id;
  64 }
  65 EXPORT_SYMBOL(idr_alloc_cyclic);
  66
  67 /**
  68  * idr_for_each - iterate through all stored pointers
  69  * @idr: idr handle
  70  * @fn: function to be called for each pointer
  71  * @data: data passed to callback function
  72  *
  73  * The callback function will be called for each entry in @idr, passing
  74  * the id, the pointer and the data pointer passed to this function.
  75  *
  76  * If @fn returns anything other than %0, the iteration stops and that
  77  * value is returned from this function.
  78  *
  79  * idr_for_each() can be called concurrently with idr_alloc() and
  80  * idr_remove() if protected by RCU.  Newly added entries may not be
  81  * seen and deleted entries may be seen, but adding and removing entries
  82  * will not cause other entries to be skipped, nor spurious ones to be seen.
  83  */
  84 int idr_for_each(const struct idr *idr,
  85                 int (*fn)(int id, void *p, void *data), void *data)
  86 {
  87         struct radix_tree_iter iter;
  88         void __rcu **slot;
  89
  90         radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
  91                 int ret = fn(iter.index, rcu_dereference_raw(*slot), data);
  92                 if (ret)
  93                         return ret;
  94         }
  95
  96         return 0;
  97 }
  98 EXPORT_SYMBOL(idr_for_each);
  99
 100 /**
 101  * idr_get_next - Find next populated entry
 102  * @idr: idr handle
 103  * @nextid: Pointer to lowest possible ID to return
 104  *
 105  * Returns the next populated entry in the tree with an ID greater than
 106  * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
 107  * to the ID of the found value.  To use in a loop, the value pointed to by
 108  * nextid must be incremented by the user.
 109  */
 110 void *idr_get_next(struct idr *idr, int *nextid)
 111 {
 112         struct radix_tree_iter iter;
 113         void __rcu **slot;
 114
 115         slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
 116         if (!slot)
 117                 return NULL;
 118
 119         *nextid = iter.index;
 120         return rcu_dereference_raw(*slot);
 121 }
 122 EXPORT_SYMBOL(idr_get_next);
 123
 124 void *idr_get_next_ext(struct idr *idr, unsigned long *nextid)
 125 {
 126         struct radix_tree_iter iter;
 127         void __rcu **slot;
 128
 129         slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
 130         if (!slot)
 131                 return NULL;
 132
 133         *nextid = iter.index;
 134         return rcu_dereference_raw(*slot);
 135 }
 136 EXPORT_SYMBOL(idr_get_next_ext);
 137
 138 /**
 139  * idr_replace - replace pointer for given id
 140  * @idr: idr handle
 141  * @ptr: New pointer to associate with the ID
 142  * @id: Lookup key
 143  *
 144  * Replace the pointer registered with an ID and return the old value.
 145  * This function can be called under the RCU read lock concurrently with
 146  * idr_alloc() and idr_remove() (as long as the ID being removed is not
 147  * the one being replaced!).
 148  *
 149  * Returns: 0 on success.  %-ENOENT indicates that @id was not found.
 150  * %-EINVAL indicates that @id or @ptr were not valid.
 151  */
 152 void *idr_replace(struct idr *idr, void *ptr, int id)
 153 {
 154         if (id < 0)
 155                 return ERR_PTR(-EINVAL);
 156
 157         return idr_replace_ext(idr, ptr, id);
 158 }
 159 EXPORT_SYMBOL(idr_replace);
 160
 161 void *idr_replace_ext(struct idr *idr, void *ptr, unsigned long id)
 162 {
 163         struct radix_tree_node *node;
 164         void __rcu **slot = NULL;
 165         void *entry;
 166
 167         if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
 168                 return ERR_PTR(-EINVAL);
 169
 170         entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
 171         if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
 172                 return ERR_PTR(-ENOENT);
 173
 174         __radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL, NULL);
 175
 176         return entry;
 177 }
 178 EXPORT_SYMBOL(idr_replace_ext);
 179
 180 /**
 181  * DOC: IDA description
 182  *
 183  * The IDA is an ID allocator which does not provide the ability to
 184  * associate an ID with a pointer.  As such, it only needs to store one
 185  * bit per ID, and so is more space efficient than an IDR.  To use an IDA,
 186  * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
 187  * then initialise it using ida_init()).  To allocate a new ID, call
 188  * ida_simple_get().  To free an ID, call ida_simple_remove().
 189  *
 190  * If you have more complex locking requirements, use a loop around
 191  * ida_pre_get() and ida_get_new() to allocate a new ID.  Then use
 192  * ida_remove() to free an ID.  You must make sure that ida_get_new() and
 193  * ida_remove() cannot be called at the same time as each other for the
 194  * same IDA.
 195  *
 196  * You can also use ida_get_new_above() if you need an ID to be allocated
 197  * above a particular number.  ida_destroy() can be used to dispose of an
 198  * IDA without needing to free the individual IDs in it.  You can use
 199  * ida_is_empty() to find out whether the IDA has any IDs currently allocated.
 200  *
 201  * IDs are currently limited to the range [0-INT_MAX].  If this is an awkward
 202  * limitation, it should be quite straightforward to raise the maximum.
 203  */
 204
 205 /*
 206  * Developer's notes:
 207  *
 208  * The IDA uses the functionality provided by the IDR & radix tree to store
 209  * bitmaps in each entry.  The IDR_FREE tag means there is at least one bit
 210  * free, unlike the IDR where it means at least one entry is free.
 211  *
 212  * I considered telling the radix tree that each slot is an order-10 node
 213  * and storing the bit numbers in the radix tree, but the radix tree can't
 214  * allow a single multiorder entry at index 0, which would significantly
 215  * increase memory consumption for the IDA.  So instead we divide the index
 216  * by the number of bits in the leaf bitmap before doing a radix tree lookup.
 217  *
 218  * As an optimisation, if there are only a few low bits set in any given
 219  * leaf, instead of allocating a 128-byte bitmap, we use the 'exceptional
 220  * entry' functionality of the radix tree to store BITS_PER_LONG - 2 bits
 221  * directly in the entry.  By being really tricksy, we could store
 222  * BITS_PER_LONG - 1 bits, but there're diminishing returns after optimising
 223  * for 0-3 allocated IDs.
 224  *
 225  * We allow the radix tree 'exceptional' count to get out of date.  Nothing
 226  * in the IDA nor the radix tree code checks it.  If it becomes important
 227  * to maintain an accurate exceptional count, switch the rcu_assign_pointer()
 228  * calls to radix_tree_iter_replace() which will correct the exceptional
 229  * count.
 230  *
 231  * The IDA always requires a lock to alloc/free.  If we add a 'test_bit'
 232  * equivalent, it will still need locking.  Going to RCU lookup would require
 233  * using RCU to free bitmaps, and that's not trivial without embedding an
 234  * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte
 235  * bitmap, which is excessive.
 236  */
 237
 238 #define IDA_MAX (0x80000000U / IDA_BITMAP_BITS)
 239
 240 /**
 241  * ida_get_new_above - allocate new ID above or equal to a start id
 242  * @ida: ida handle
 243  * @start: id to start search at
 244  * @id: pointer to the allocated handle
 245  *
 246  * Allocate new ID above or equal to @start.  It should be called
 247  * with any required locks to ensure that concurrent calls to
 248  * ida_get_new_above() / ida_get_new() / ida_remove() are not allowed.
 249  * Consider using ida_simple_get() if you do not have complex locking
 250  * requirements.
 251  *
 252  * If memory is required, it will return %-EAGAIN, you should unlock
 253  * and go back to the ida_pre_get() call.  If the ida is full, it will
 254  * return %-ENOSPC.  On success, it will return 0.
 255  *
 256  * @id returns a value in the range @start ... %0x7fffffff.
 257  */
 258 int ida_get_new_above(struct ida *ida, int start, int *id)
 259 {
 260         struct radix_tree_root *root = &ida->ida_rt;
 261         void __rcu **slot;
 262         struct radix_tree_iter iter;
 263         struct ida_bitmap *bitmap;
 264         unsigned long index;
 265         unsigned bit, ebit;
 266         int new;
 267
 268         index = start / IDA_BITMAP_BITS;
 269         bit = start % IDA_BITMAP_BITS;
 270         ebit = bit + RADIX_TREE_EXCEPTIONAL_SHIFT;
 271
 272         slot = radix_tree_iter_init(&iter, index);
 273         for (;;) {
 274                 if (slot)
 275                         slot = radix_tree_next_slot(slot, &iter,
 276                                                 RADIX_TREE_ITER_TAGGED);
 277                 if (!slot) {
 278                         slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX);
 279                         if (IS_ERR(slot)) {
 280                                 if (slot == ERR_PTR(-ENOMEM))
 281                                         return -EAGAIN;
 282                                 return PTR_ERR(slot);
 283                         }
 284                 }
 285                 if (iter.index > index) {
 286                         bit = 0;
 287                         ebit = RADIX_TREE_EXCEPTIONAL_SHIFT;
 288                 }
 289                 new = iter.index * IDA_BITMAP_BITS;
 290                 bitmap = rcu_dereference_raw(*slot);
 291                 if (radix_tree_exception(bitmap)) {
 292                         unsigned long tmp = (unsigned long)bitmap;
 293                         ebit = find_next_zero_bit(&tmp, BITS_PER_LONG, ebit);
 294                         if (ebit < BITS_PER_LONG) {
 295                                 tmp |= 1UL << ebit;
 296                                 rcu_assign_pointer(*slot, (void *)tmp);
 297                                 *id = new + ebit - RADIX_TREE_EXCEPTIONAL_SHIFT;
 298                                 return 0;
 299                         }
 300                         bitmap = this_cpu_xchg(ida_bitmap, NULL);
 301                         if (!bitmap)
 302                                 return -EAGAIN;
 303                         memset(bitmap, 0, sizeof(*bitmap));
 304                         bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
 305                         rcu_assign_pointer(*slot, bitmap);
 306                 }
 307
 308                 if (bitmap) {
 309                         bit = find_next_zero_bit(bitmap->bitmap,
 310                                                         IDA_BITMAP_BITS, bit);
 311                         new += bit;
 312                         if (new < 0)
 313                                 return -ENOSPC;
 314                         if (bit == IDA_BITMAP_BITS)
 315                                 continue;
 316
 317                         __set_bit(bit, bitmap->bitmap);
 318                         if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
 319                                 radix_tree_iter_tag_clear(root, &iter,
 320                                                                 IDR_FREE);
 321                 } else {
 322                         new += bit;
 323                         if (new < 0)
 324                                 return -ENOSPC;
 325                         if (ebit < BITS_PER_LONG) {
 326                                 bitmap = (void *)((1UL << ebit) |
 327                                                 RADIX_TREE_EXCEPTIONAL_ENTRY);
 328                                 radix_tree_iter_replace(root, &iter, slot,
 329                                                 bitmap);
 330                                 *id = new;
 331                                 return 0;
 332                         }
 333                         bitmap = this_cpu_xchg(ida_bitmap, NULL);
 334                         if (!bitmap)
 335                                 return -EAGAIN;
 336                         memset(bitmap, 0, sizeof(*bitmap));
 337                         __set_bit(bit, bitmap->bitmap);
 338                         radix_tree_iter_replace(root, &iter, slot, bitmap);
 339                 }
 340
 341                 *id = new;
 342                 return 0;
 343         }
 344 }
 345 EXPORT_SYMBOL(ida_get_new_above);
 346
 347 /**
 348  * ida_remove - Free the given ID
 349  * @ida: ida handle
 350  * @id: ID to free
 351  *
 352  * This function should not be called at the same time as ida_get_new_above().
 353  */
 354 void ida_remove(struct ida *ida, int id)
 355 {
 356         unsigned long index = id / IDA_BITMAP_BITS;
 357         unsigned offset = id % IDA_BITMAP_BITS;
 358         struct ida_bitmap *bitmap;
 359         unsigned long *btmp;
 360         struct radix_tree_iter iter;
 361         void __rcu **slot;
 362
 363         slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index);
 364         if (!slot)
 365                 goto err;
 366
 367         bitmap = rcu_dereference_raw(*slot);
 368         if (radix_tree_exception(bitmap)) {
 369                 btmp = (unsigned long *)slot;
 370                 offset += RADIX_TREE_EXCEPTIONAL_SHIFT;
 371                 if (offset >= BITS_PER_LONG)
 372                         goto err;
 373         } else {
 374                 btmp = bitmap->bitmap;
 375         }
 376         if (!test_bit(offset, btmp))
 377                 goto err;
 378
 379         __clear_bit(offset, btmp);
 380         radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE);
 381         if (radix_tree_exception(bitmap)) {
 382                 if (rcu_dereference_raw(*slot) ==
 383                                         (void *)RADIX_TREE_EXCEPTIONAL_ENTRY)
 384                         radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 385         } else if (bitmap_empty(btmp, IDA_BITMAP_BITS)) {
 386                 kfree(bitmap);
 387                 radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 388         }
 389         return;
 390  err:
 391         WARN(1, "ida_remove called for id=%d which is not allocated.\n", id);
 392 }
 393 EXPORT_SYMBOL(ida_remove);
 394
 395 /**
 396  * ida_destroy - Free the contents of an ida
 397  * @ida: ida handle
 398  *
 399  * Calling this function releases all resources associated with an IDA.  When
 400  * this call returns, the IDA is empty and can be reused or freed.  The caller
 401  * should not allow ida_remove() or ida_get_new_above() to be called at the
 402  * same time.
 403  */
 404 void ida_destroy(struct ida *ida)
 405 {
 406         struct radix_tree_iter iter;
 407         void __rcu **slot;
 408
 409         radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
 410                 struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);
 411                 if (!radix_tree_exception(bitmap))
 412                         kfree(bitmap);
 413                 radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 414         }
 415 }
 416 EXPORT_SYMBOL(ida_destroy);
 417
 418 /**
 419  * ida_simple_get - get a new id.
 420  * @ida: the (initialized) ida.
 421  * @start: the minimum id (inclusive, < 0x8000000)
 422  * @end: the maximum id (exclusive, < 0x8000000 or 0)
 423  * @gfp_mask: memory allocation flags
 424  *
 425  * Allocates an id in the range start <= id < end, or returns -ENOSPC.
 426  * On memory allocation failure, returns -ENOMEM.
 427  *
 428  * Compared to ida_get_new_above() this function does its own locking, and
 429  * should be used unless there are special requirements.
 430  *
 431  * Use ida_simple_remove() to get rid of an id.
 432  */
 433 int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
 434                    gfp_t gfp_mask)
 435 {
 436         int ret, id;
 437         unsigned int max;
 438         unsigned long flags;
 439
 440         BUG_ON((int)start < 0);
 441         BUG_ON((int)end < 0);
 442
 443         if (end == 0)
 444                 max = 0x80000000;
 445         else {
 446                 BUG_ON(end < start);
 447                 max = end - 1;
 448         }
 449
 450 again:
 451         if (!ida_pre_get(ida, gfp_mask))
 452                 return -ENOMEM;
 453
 454         spin_lock_irqsave(&simple_ida_lock, flags);
 455         ret = ida_get_new_above(ida, start, &id);
 456         if (!ret) {
 457                 if (id > max) {
 458                         ida_remove(ida, id);
 459                         ret = -ENOSPC;
 460                 } else {
 461                         ret = id;
 462                 }
 463         }
 464         spin_unlock_irqrestore(&simple_ida_lock, flags);
 465
 466         if (unlikely(ret == -EAGAIN))
 467                 goto again;
 468
 469         return ret;
 470 }
 471 EXPORT_SYMBOL(ida_simple_get);
 472
 473 /**
 474  * ida_simple_remove - remove an allocated id.
 475  * @ida: the (initialized) ida.
 476  * @id: the id returned by ida_simple_get.
 477  *
 478  * Use to release an id allocated with ida_simple_get().
 479  *
 480  * Compared to ida_remove() this function does its own locking, and should be
 481  * used unless there are special requirements.
 482  */
 483 void ida_simple_remove(struct ida *ida, unsigned int id)
 484 {
 485         unsigned long flags;
 486
 487         BUG_ON((int)id < 0);
 488         spin_lock_irqsave(&simple_ida_lock, flags);
 489         ida_remove(ida, id);
 490         spin_unlock_irqrestore(&simple_ida_lock, flags);
 491 }
 492 EXPORT_SYMBOL(ida_simple_remove);