aboutsummaryrefslogtreecommitdiff
path: root/lib/idr.c
blob: edd9b2be1651fa99ae3a6274bda38c1bd7159a64 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
#include <linux/bitmap.h>
#include <linux/export.h>
#include <linux/idr.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);
static DEFINE_SPINLOCK(simple_ida_lock);

int idr_alloc_cmn(struct idr *idr, void *ptr, unsigned long *index,
		  unsigned long start, unsigned long end, gfp_t gfp,
		  bool ext)
{
	struct radix_tree_iter iter;
	void __rcu **slot;

	if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
		return -EINVAL;

	radix_tree_iter_init(&iter, start);
	if (ext)
		slot = idr_get_free_ext(&idr->idr_rt, &iter, gfp, end);
	else
		slot = idr_get_free(&idr->idr_rt, &iter, gfp, end);
	if (IS_ERR(slot))
		return PTR_ERR(slot);

	radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
	radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);

	if (index)
		*index = iter.index;
	return 0;
}
EXPORT_SYMBOL_GPL(idr_alloc_cmn);

/**
 * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
 * @idr: idr handle
 * @ptr: pointer to be associated with the new id
 * @start: the minimum id (inclusive)
 * @end: the maximum id (exclusive)
 * @gfp: memory allocation flags
 *
 * Allocates an ID larger than the last ID allocated if one is available.
 * If not, it will attempt to allocate the smallest ID that is larger or
 * equal to @start.
 */
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
	int id, curr = idr->idr_next;

	if (curr < start)
		curr = start;

	id = idr_alloc(idr, ptr, curr, end, gfp);
	if ((id == -ENOSPC) && (curr > start))
		id = idr_alloc(idr, ptr, start, curr, gfp);

	if (id >= 0)
		idr->idr_next = id + 1U;

	return id;
}
EXPORT_SYMBOL(idr_alloc_cyclic);

/**
 * idr_for_each - iterate through all stored pointers
 * @idr: idr handle
 * @fn: function to be called for each pointer
 * @data: data passed to callback function
 *
 * The callback function will be called for each entry in @idr, passing
 * the id, the pointer and the data pointer passed to this function.
 *
 * If @fn returns anything other than %0, the iteration stops and that
 * value is returned from this function.
 *
 * idr_for_each() can be called concurrently with idr_alloc() and
 * idr_remove() if protected by RCU.  Newly added entries may not be
 * seen and deleted entries may be seen, but adding and removing entries
 * will not cause other entries to be skipped, nor spurious ones to be seen.
 */
int idr_for_each(const struct idr *idr,
		int (*fn)(int id, void *p, void *data), void *data)
{
	struct radix_tree_iter iter;
	void __rcu **slot;

	radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
		int ret = fn(iter.index, rcu_dereference_raw(*slot), data);
		if (ret)
			return ret;
	}

	return 0;
}
EXPORT_SYMBOL(idr_for_each);

/**
 * idr_get_next - Find next populated entry
 * @idr: idr handle
 * @nextid: Pointer to lowest possible ID to return
 *
 * Returns the next populated entry in the tree with an ID greater than
 * or equal to the value pointed to by @nextid.  On exit, @nextid is updated
 * to the ID of the found value.  To use in a loop, the value pointed to by
 * nextid must be incremented by the user.
 */
void *idr_get_next(struct idr *idr, int *nextid)
{
	struct radix_tree_iter iter;
	void __rcu **slot;

	slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
	if (!slot)
		return NULL;

	*nextid = iter.index;
	return rcu_dereference_raw(*slot);
}
EXPORT_SYMBOL(idr_get_next);

void *idr_get_next_ext(struct idr *idr, unsigned long *nextid)
{
	struct radix_tree_iter iter;
	void __rcu **slot;

	slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
	if (!slot)
		return NULL;

	*nextid = iter.index;
	return rcu_dereference_raw(*slot);
}
EXPORT_SYMBOL(idr_get_next_ext);

/**
 * idr_replace - replace pointer for given id
 * @idr: idr handle
 * @ptr: New pointer to associate with the ID
 * @id: Lookup key
 *
 * Replace the pointer registered with an ID and return the old value.
 * This function can be called under the RCU read lock concurrently with
 * idr_alloc() and idr_remove() (as long as the ID being removed is not
 * the one being replaced!).
 *
 * Returns: the old value on success.  %-ENOENT indicates that @id was not
 * found.  %-EINVAL indicates that @id or @ptr were not valid.
 */
void *idr_replace(struct idr *idr, void *ptr, int id)
{
	if (id < 0)
		return ERR_PTR(-EINVAL);

	return idr_replace_ext(idr, ptr, id);
}
EXPORT_SYMBOL(idr_replace);

void *idr_replace_ext(struct idr *idr, void *ptr, unsigned long id)
{
	struct radix_tree_node *node;
	void __rcu **slot = NULL;
	void *entry;

	if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
		return ERR_PTR(-EINVAL);

	entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
	if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
		return ERR_PTR(-ENOENT);

	__radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL, NULL);

	return entry;
}
EXPORT_SYMBOL(idr_replace_ext);

/**
 * DOC: IDA description
 *
 * The IDA is an ID allocator which does not provide the ability to
 * associate an ID with a pointer.  As such, it only needs to store one
 * bit per ID, and so is more space efficient than an IDR.  To use an IDA,
 * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
 * then initialise it using ida_init()).  To allocate a new ID, call
 * ida_simple_get().  To free an ID, call ida_simple_remove().
 *
 * If you have more complex locking requirements, use a loop around
 * ida_pre_get() and ida_get_new() to allocate a new ID.  Then use
 * ida_remove() to free an ID.  You must make sure that ida_get_new() and
 * ida_remove() cannot be called at the same time as each other for the
 * same IDA.
 *
 * You can also use ida_get_new_above() if you need an ID to be allocated
 * above a particular number.  ida_destroy() can be used to dispose of an
 * IDA without needing to free the individual IDs in it.  You can use
 * ida_is_empty() to find out whether the IDA has any IDs currently allocated.
 *
 * IDs are currently limited to the range [0-INT_MAX].  If this is an awkward
 * limitation, it should be quite straightforward to raise the maximum.
 */

/*
 * Developer's notes:
 *
 * The IDA uses the functionality provided by the IDR & radix tree to store
 * bitmaps in each entry.  The IDR_FREE tag means there is at least one bit
 * free, unlike the IDR where it means at least one entry is free.
 *
 * I considered telling the radix tree that each slot is an order-10 node
 * and storing the bit numbers in the radix tree, but the radix tree can't
 * allow a single multiorder entry at index 0, which would significantly
 * increase memory consumption for the IDA.  So instead we divide the index
 * by the number of bits in the leaf bitmap before doing a radix tree lookup.
 *
 * As an optimisation, if there are only a few low bits set in any given
 * leaf, instead of allocating a 128-byte bitmap, we use the 'exceptional
 * entry' functionality of the radix tree to store BITS_PER_LONG - 2 bits
 * directly in the entry.  By being really tricksy, we could store
 * BITS_PER_LONG - 1 bits, but there're diminishing returns after optimising
 * for 0-3 allocated IDs.
 *
 * We allow the radix tree 'exceptional' count to get out of date.  Nothing
 * in the IDA nor the radix tree code checks it.  If it becomes important
 * to maintain an accurate exceptional count, switch the rcu_assign_pointer()
 * calls to radix_tree_iter_replace() which will correct the exceptional
 * count.
 *
 * The IDA always requires a lock to alloc/free.  If we add a 'test_bit'
 * equivalent, it will still need locking.  Going to RCU lookup would require
 * using RCU to free bitmaps, and that's not trivial without embedding an
 * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte
 * bitmap, which is excessive.
 */

#define IDA_MAX (0x80000000U / IDA_BITMAP_BITS)

/**
 * ida_get_new_above - allocate new ID above or equal to a start id
 * @ida: ida handle
 * @start: id to start search at
 * @id: pointer to the allocated handle
 *
 * Allocate new ID above or equal to @start.  It should be called
 * with any required locks to ensure that concurrent calls to
 * ida_get_new_above() / ida_get_new() / ida_remove() are not allowed.
 * Consider using ida_simple_get() if you do not have complex locking
 * requirements.
 *
 * If memory is required, it will return %-EAGAIN, you should unlock
 * and go back to the ida_pre_get() call.  If the ida is full, it will
 * return %-ENOSPC.  On success, it will return 0.
 *
 * @id returns a value in the range @start ... %0x7fffffff.
 */
int ida_get_new_above(struct ida *ida, int start, int *id)
{
	struct radix_tree_root *root = &ida->ida_rt;
	void __rcu **slot;
	struct radix_tree_iter iter;
	struct ida_bitmap *bitmap;
	unsigned long index;
	unsigned bit, ebit;
	int new;

	index = start / IDA_BITMAP_BITS;
	bit = start % IDA_BITMAP_BITS;
	ebit = bit + RADIX_TREE_EXCEPTIONAL_SHIFT;

	slot = radix_tree_iter_init(&iter, index);
	for (;;) {
		if (slot)
			slot = radix_tree_next_slot(slot, &iter,
						RADIX_TREE_ITER_TAGGED);
		if (!slot) {
			slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX);
			if (IS_ERR(slot)) {
				if (slot == ERR_PTR(-ENOMEM))
					return -EAGAIN;
				return PTR_ERR(slot);
			}
		}
		if (iter.index > index) {
			bit = 0;
			ebit = RADIX_TREE_EXCEPTIONAL_SHIFT;
		}
		new = iter.index * IDA_BITMAP_BITS;
		bitmap = rcu_dereference_raw(*slot);
		if (radix_tree_exception(bitmap)) {
			unsigned long tmp = (unsigned long)bitmap;
			ebit = find_next_zero_bit(&tmp, BITS_PER_LONG, ebit);
			if (ebit < BITS_PER_LONG) {
				tmp |= 1UL << ebit;
				rcu_assign_pointer(*slot, (void *)tmp);
				*id = new + ebit - RADIX_TREE_EXCEPTIONAL_SHIFT;
				return 0;
			}
			bitmap = this_cpu_xchg(ida_bitmap, NULL);
			if (!bitmap)
				return -EAGAIN;
			memset(bitmap, 0, sizeof(*bitmap));
			bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
			rcu_assign_pointer(*slot, bitmap);
		}

		if (bitmap) {
			bit = find_next_zero_bit(bitmap->bitmap,
							IDA_BITMAP_BITS, bit);
			new += bit;
			if (new < 0)
				return -ENOSPC;
			if (bit == IDA_BITMAP_BITS)
				continue;

			__set_bit(bit, bitmap->bitmap);
			if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
				radix_tree_iter_tag_clear(root, &iter,
								IDR_FREE);
		} else {
			new += bit;
			if (new < 0)
				return -ENOSPC;
			if (ebit < BITS_PER_LONG) {
				bitmap = (void *)((1UL << ebit) |
						RADIX_TREE_EXCEPTIONAL_ENTRY);
				radix_tree_iter_replace(root, &iter, slot,
						bitmap);
				*id = new;
				return 0;
			}
			bitmap = this_cpu_xchg(ida_bitmap, NULL);
			if (!bitmap)
				return -EAGAIN;
			memset(bitmap, 0, sizeof(*bitmap));
			__set_bit(bit, bitmap->bitmap);
			radix_tree_iter_replace(root, &iter, slot, bitmap);
		}

		*id = new;
		return 0;
	}
}
EXPORT_SYMBOL(ida_get_new_above);

/**
 * ida_remove - Free the given ID
 * @ida: ida handle
 * @id: ID to free
 *
 * This function should not be called at the same time as ida_get_new_above().
 */
void ida_remove(struct ida *ida, int id)
{
	unsigned long index = id / IDA_BITMAP_BITS;
	unsigned offset = id % IDA_BITMAP_BITS;
	struct ida_bitmap *bitmap;
	unsigned long *btmp;
	struct radix_tree_iter iter;
	void __rcu **slot;

	slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index);
	if (!slot)
		goto err;

	bitmap = rcu_dereference_raw(*slot);
	if (radix_tree_exception(bitmap)) {
		btmp = (unsigned long *)slot;
		offset += RADIX_TREE_EXCEPTIONAL_SHIFT;
		if (offset >= BITS_PER_LONG)
			goto err;
	} else {
		btmp = bitmap->bitmap;
	}
	if (!test_bit(offset, btmp))
		goto err;

	__clear_bit(offset, btmp);
	radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE);
	if (radix_tree_exception(bitmap)) {
		if (rcu_dereference_raw(*slot) ==
					(void *)RADIX_TREE_EXCEPTIONAL_ENTRY)
			radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
	} else if (bitmap_empty(btmp, IDA_BITMAP_BITS)) {
		kfree(bitmap);
		radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
	}
	return;
 err:
	WARN(1, "ida_remove called for id=%d which is not allocated.\n", id);
}
EXPORT_SYMBOL(ida_remove);

/**
 * ida_destroy - Free the contents of an ida
 * @ida: ida handle
 *
 * Calling this function releases all resources associated with an IDA.  When
 * this call returns, the IDA is empty and can be reused or freed.  The caller
 * should not allow ida_remove() or ida_get_new_above() to be called at the
 * same time.
 */
void ida_destroy(struct ida *ida)
{
	struct radix_tree_iter iter;
	void __rcu **slot;

	radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
		struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);
		if (!radix_tree_exception(bitmap))
			kfree(bitmap);
		radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
	}
}
EXPORT_SYMBOL(ida_destroy);

/**
 * ida_simple_get - get a new id.
 * @ida: the (initialized) ida.
 * @start: the minimum id (inclusive, < 0x8000000)
 * @end: the maximum id (exclusive, < 0x8000000 or 0)
 * @gfp_mask: memory allocation flags
 *
 * Allocates an id in the range start <= id < end, or returns -ENOSPC.
 * On memory allocation failure, returns -ENOMEM.
 *
 * Compared to ida_get_new_above() this function does its own locking, and
 * should be used unless there are special requirements.
 *
 * Use ida_simple_remove() to get rid of an id.
 */
int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
		   gfp_t gfp_mask)
{
	int ret, id;
	unsigned int max;
	unsigned long flags;

	BUG_ON((int)start < 0);
	BUG_ON((int)end < 0);

	if (end == 0)
		max = 0x80000000;
	else {
		BUG_ON(end < start);
		max = end - 1;
	}

again:
	if (!ida_pre_get(ida, gfp_mask))
		return -ENOMEM;

	spin_lock_irqsave(&simple_ida_lock, flags);
	ret = ida_get_new_above(ida, start, &id);
	if (!ret) {
		if (id > max) {
			ida_remove(ida, id);
			ret = -ENOSPC;
		} else {
			ret = id;
		}
	}
	spin_unlock_irqrestore(&simple_ida_lock, flags);

	if (unlikely(ret == -EAGAIN))
		goto again;

	return ret;
}
EXPORT_SYMBOL(ida_simple_get);

/**
 * ida_simple_remove - remove an allocated id.
 * @ida: the (initialized) ida.
 * @id: the id returned by ida_simple_get.
 *
 * Use to release an id allocated with ida_simple_get().
 *
 * Compared to ida_remove() this function does its own locking, and should be
 * used unless there are special requirements.
 */
void ida_simple_remove(struct ida *ida, unsigned int id)
{
	unsigned long flags;

	BUG_ON((int)id < 0);
	spin_lock_irqsave(&simple_ida_lock, flags);
	ida_remove(ida, id);
	spin_unlock_irqrestore(&simple_ida_lock, flags);
}
EXPORT_SYMBOL(ida_simple_remove);