summaryrefslogtreecommitdiff
path: root/lib/idr.c
blob: 9a366b5be2c29a5ee675c26590583c3ff334e168 (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
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
#include <linux/bitmap.h>
#include <linux/bug.h>
#include <linux/export.h>
#include <linux/idr.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/xarray.h>

DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);

/**
 * idr_alloc_u32() - Allocate an ID.
 * @idr: IDR handle.
 * @ptr: Pointer to be associated with the new ID.
 * @nextid: Pointer to an ID.
 * @max: The maximum ID to allocate (inclusive).
 * @gfp: Memory allocation flags.
 *
 * Allocates an unused ID in the range specified by @nextid and @max.
 * Note that @max is inclusive whereas the @end parameter to idr_alloc()
 * is exclusive.  The new ID is assigned to @nextid before the pointer
 * is inserted into the IDR, so if @nextid points into the object pointed
 * to by @ptr, a concurrent lookup will not find an uninitialised ID.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: 0 if an ID was allocated, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.  If an error occurred,
 * @nextid is unchanged.
 */
int idr_alloc_u32(struct idr *idr, void *ptr, u32 *nextid,
			unsigned long max, gfp_t gfp)
{
	struct radix_tree_iter iter;
	void __rcu **slot;
	unsigned int base = idr->idr_base;
	unsigned int id = *nextid;

	if (WARN_ON_ONCE(!(idr->idr_rt.xa_flags & ROOT_IS_IDR)))
		idr->idr_rt.xa_flags |= IDR_RT_MARKER;

	id = (id < base) ? 0 : id - base;
	radix_tree_iter_init(&iter, id);
	slot = idr_get_free(&idr->idr_rt, &iter, gfp, max - base);
	if (IS_ERR(slot))
		return PTR_ERR(slot);

	*nextid = iter.index + base;
	/* there is a memory barrier inside radix_tree_iter_replace() */
	radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
	radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);

	return 0;
}
EXPORT_SYMBOL_GPL(idr_alloc_u32);

/**
 * idr_alloc() - Allocate an ID.
 * @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 unused ID in the range specified by @start and @end.  If
 * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
 * callers to use @start + N as @end as long as N is within integer range.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.
 */
int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
	u32 id = start;
	int ret;

	if (WARN_ON_ONCE(start < 0))
		return -EINVAL;

	ret = idr_alloc_u32(idr, ptr, &id, end > 0 ? end - 1 : INT_MAX, gfp);
	if (ret)
		return ret;

	return id;
}
EXPORT_SYMBOL_GPL(idr_alloc);

/**
 * idr_alloc_cyclic() - Allocate an ID cyclically.
 * @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 unused ID in the range specified by @nextid and @end.  If
 * @end is <= 0, it is treated as one larger than %INT_MAX.  This allows
 * callers to use @start + N as @end as long as N is within integer range.
 * The search for an unused ID will start at the last ID allocated and will
 * wrap around to @start if no free IDs are found before reaching @end.
 *
 * The caller should provide their own locking to ensure that two
 * concurrent modifications to the IDR are not possible.  Read-only
 * accesses to the IDR may be done under the RCU read lock or may
 * exclude simultaneous writers.
 *
 * Return: The newly allocated ID, -ENOMEM if memory allocation failed,
 * or -ENOSPC if no free IDs could be found.
 */
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
	u32 id = idr->idr_next;
	int err, max = end > 0 ? end - 1 : INT_MAX;

	if ((int)id < start)
		id = start;

	err = idr_alloc_u32(idr, ptr, &id, max, gfp);
	if ((err == -ENOSPC) && (id > start)) {
		id = start;
		err = idr_alloc_u32(idr, ptr, &id, max, gfp);
	}
	if (err)
		return err;

	idr->idr_next = id + 1;
	return id;
}
EXPORT_SYMBOL(idr_alloc_cyclic);

/**
 * idr_remove() - Remove an ID from the IDR.
 * @idr: IDR handle.
 * @id: Pointer ID.
 *
 * Removes this ID from the IDR.  If the ID was not previously in the IDR,
 * this function returns %NULL.
 *
 * Since this function modifies the IDR, the caller should provide their
 * own locking to ensure that concurrent modification of the same IDR is
 * not possible.
 *
 * Return: The pointer formerly associated with this ID.
 */
void *idr_remove(struct idr *idr, unsigned long id)
{
	return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
}
EXPORT_SYMBOL_GPL(idr_remove);

/**
 * idr_find() - Return pointer for given ID.
 * @idr: IDR handle.
 * @id: Pointer ID.
 *
 * Looks up the pointer associated with this ID.  A %NULL pointer may
 * indicate that @id is not allocated or that the %NULL pointer was
 * associated with this ID.
 *
 * This function can be called under rcu_read_lock(), given that the leaf
 * pointers lifetimes are correctly managed.
 *
 * Return: The pointer associated with this ID.
 */
void *idr_find(const struct idr *idr, unsigned long id)
{
	return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
}
EXPORT_SYMBOL_GPL(idr_find);

/**
 * 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 entry and @data.
 *
 * 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;
	int base = idr->idr_base;

	radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
		int ret;
		unsigned long id = iter.index + base;

		if (WARN_ON_ONCE(id > INT_MAX))
			break;
		ret = fn(id, 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 an ID.
 *
 * 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;
	unsigned long base = idr->idr_base;
	unsigned long id = *nextid;

	id = (id < base) ? 0 : id - base;
	slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
	if (!slot)
		return NULL;
	id = iter.index + base;

	if (WARN_ON_ONCE(id > INT_MAX))
		return NULL;

	*nextid = id;
	return rcu_dereference_raw(*slot);
}
EXPORT_SYMBOL(idr_get_next);

/**
 * idr_get_next_ul() - Find next populated entry.
 * @idr: IDR handle.
 * @nextid: Pointer to an ID.
 *
 * 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_ul(struct idr *idr, unsigned long *nextid)
{
	struct radix_tree_iter iter;
	void __rcu **slot;
	unsigned long base = idr->idr_base;
	unsigned long id = *nextid;

	id = (id < base) ? 0 : id - base;
	slot = radix_tree_iter_find(&idr->idr_rt, &iter, id);
	if (!slot)
		return NULL;

	*nextid = iter.index + base;
	return rcu_dereference_raw(*slot);
}
EXPORT_SYMBOL(idr_get_next_ul);

/**
 * idr_replace() - replace pointer for given ID.
 * @idr: IDR handle.
 * @ptr: New pointer to associate with the ID.
 * @id: ID to change.
 *
 * 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 @ptr was not valid.
 */
void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
{
	struct radix_tree_node *node;
	void __rcu **slot = NULL;
	void *entry;

	id -= idr->idr_base;

	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);

	return entry;
}
EXPORT_SYMBOL(idr_replace);

/**
 * 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_alloc(), ida_alloc_min(), ida_alloc_max() or ida_alloc_range().
 * To free an ID, call ida_free().
 *
 * 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 store the bits
 * directly in the entry.
 *
 * 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 - 1)

static int ida_get_new_above(struct ida *ida, int start)
{
	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;
	int new;

	index = start / IDA_BITMAP_BITS;
	bit = start % IDA_BITMAP_BITS;

	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;
		new = iter.index * IDA_BITMAP_BITS;
		bitmap = rcu_dereference_raw(*slot);
		if (xa_is_value(bitmap)) {
			unsigned long tmp = xa_to_value(bitmap);
			int vbit = find_next_zero_bit(&tmp, BITS_PER_XA_VALUE,
							bit);
			if (vbit < BITS_PER_XA_VALUE) {
				tmp |= 1UL << vbit;
				rcu_assign_pointer(*slot, xa_mk_value(tmp));
				return new + vbit;
			}
			bitmap = this_cpu_xchg(ida_bitmap, NULL);
			if (!bitmap)
				return -EAGAIN;
			bitmap->bitmap[0] = tmp;
			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 (bit < BITS_PER_XA_VALUE) {
				bitmap = xa_mk_value(1UL << bit);
			} else {
				bitmap = this_cpu_xchg(ida_bitmap, NULL);
				if (!bitmap)
					return -EAGAIN;
				__set_bit(bit, bitmap->bitmap);
			}
			radix_tree_iter_replace(root, &iter, slot, bitmap);
		}

		return new;
	}
}

static 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 (xa_is_value(bitmap)) {
		btmp = (unsigned long *)slot;
		offset += 1; /* Intimate knowledge of the value encoding */
		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 (xa_is_value(bitmap)) {
		if (xa_to_value(rcu_dereference_raw(*slot)) == 0)
			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_free called for id=%d which is not allocated.\n", id);
}

/**
 * ida_destroy() - Free all IDs.
 * @ida: IDA handle.
 *
 * Calling this function frees all IDs and releases all resources used
 * by an IDA.  When this call returns, the IDA is empty and can be reused
 * or freed.  If the IDA is already empty, there is no need to call this
 * function.
 *
 * Context: Any context.
 */
void ida_destroy(struct ida *ida)
{
	unsigned long flags;
	struct radix_tree_iter iter;
	void __rcu **slot;

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

/**
 * ida_alloc_range() - Allocate an unused ID.
 * @ida: IDA handle.
 * @min: Lowest ID to allocate.
 * @max: Highest ID to allocate.
 * @gfp: Memory allocation flags.
 *
 * Allocate an ID between @min and @max, inclusive.  The allocated ID will
 * not exceed %INT_MAX, even if @max is larger.
 *
 * Context: Any context.
 * Return: The allocated ID, or %-ENOMEM if memory could not be allocated,
 * or %-ENOSPC if there are no free IDs.
 */
int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,
			gfp_t gfp)
{
	int id = 0;
	unsigned long flags;

	if ((int)min < 0)
		return -ENOSPC;

	if ((int)max < 0)
		max = INT_MAX;

again:
	xa_lock_irqsave(&ida->ida_rt, flags);
	id = ida_get_new_above(ida, min);
	if (id > (int)max) {
		ida_remove(ida, id);
		id = -ENOSPC;
	}
	xa_unlock_irqrestore(&ida->ida_rt, flags);

	if (unlikely(id == -EAGAIN)) {
		if (!ida_pre_get(ida, gfp))
			return -ENOMEM;
		goto again;
	}

	return id;
}
EXPORT_SYMBOL(ida_alloc_range);

/**
 * ida_free() - Release an allocated ID.
 * @ida: IDA handle.
 * @id: Previously allocated ID.
 *
 * Context: Any context.
 */
void ida_free(struct ida *ida, unsigned int id)
{
	unsigned long flags;

	BUG_ON((int)id < 0);
	xa_lock_irqsave(&ida->ida_rt, flags);
	ida_remove(ida, id);
	xa_unlock_irqrestore(&ida->ida_rt, flags);
}
EXPORT_SYMBOL(ida_free);