1 #include <linux/bitmap.h>
2 #include <linux/export.h>
4 #include <linux/slab.h>
5 #include <linux/spinlock.h>
7 DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);
8 static DEFINE_SPINLOCK(simple_ida_lock);
11 * idr_alloc - allocate an id
13 * @ptr: pointer to be associated with the new id
14 * @start: the minimum id (inclusive)
15 * @end: the maximum id (exclusive)
16 * @gfp: memory allocation flags
18 * Allocates an unused ID in the range [start, end). Returns -ENOSPC
19 * if there are no unused IDs in that range.
21 * Note that @end is treated as max when <= 0. This is to always allow
22 * using @start + N as @end as long as N is inside integer range.
24 * Simultaneous modifications to the @idr are not allowed and should be
25 * prevented by the user, usually with a lock. idr_alloc() may be called
26 * concurrently with read-only accesses to the @idr, such as idr_find() and
27 * idr_for_each_entry().
29 int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
32 struct radix_tree_iter iter;
34 if (WARN_ON_ONCE(start < 0))
36 if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
39 radix_tree_iter_init(&iter, start);
40 slot = idr_get_free(&idr->idr_rt, &iter, gfp, end);
44 radix_tree_iter_replace(&idr->idr_rt, &iter, slot, ptr);
45 radix_tree_iter_tag_clear(&idr->idr_rt, &iter, IDR_FREE);
48 EXPORT_SYMBOL_GPL(idr_alloc);
51 * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
53 * @ptr: pointer to be associated with the new id
54 * @start: the minimum id (inclusive)
55 * @end: the maximum id (exclusive)
56 * @gfp: memory allocation flags
58 * Allocates an ID larger than the last ID allocated if one is available.
59 * If not, it will attempt to allocate the smallest ID that is larger or
62 int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
64 int id, curr = idr->idr_next;
69 id = idr_alloc(idr, ptr, curr, end, gfp);
70 if ((id == -ENOSPC) && (curr > start))
71 id = idr_alloc(idr, ptr, start, curr, gfp);
74 idr->idr_next = id + 1U;
78 EXPORT_SYMBOL(idr_alloc_cyclic);
81 * idr_for_each - iterate through all stored pointers
83 * @fn: function to be called for each pointer
84 * @data: data passed to callback function
86 * The callback function will be called for each entry in @idr, passing
87 * the id, the pointer and the data pointer passed to this function.
89 * If @fn returns anything other than %0, the iteration stops and that
90 * value is returned from this function.
92 * idr_for_each() can be called concurrently with idr_alloc() and
93 * idr_remove() if protected by RCU. Newly added entries may not be
94 * seen and deleted entries may be seen, but adding and removing entries
95 * will not cause other entries to be skipped, nor spurious ones to be seen.
97 int idr_for_each(const struct idr *idr,
98 int (*fn)(int id, void *p, void *data), void *data)
100 struct radix_tree_iter iter;
103 radix_tree_for_each_slot(slot, &idr->idr_rt, &iter, 0) {
104 int ret = fn(iter.index, rcu_dereference_raw(*slot), data);
111 EXPORT_SYMBOL(idr_for_each);
114 * idr_get_next - Find next populated entry
116 * @nextid: Pointer to lowest possible ID to return
118 * Returns the next populated entry in the tree with an ID greater than
119 * or equal to the value pointed to by @nextid. On exit, @nextid is updated
120 * to the ID of the found value. To use in a loop, the value pointed to by
121 * nextid must be incremented by the user.
123 void *idr_get_next(struct idr *idr, int *nextid)
125 struct radix_tree_iter iter;
128 slot = radix_tree_iter_find(&idr->idr_rt, &iter, *nextid);
132 *nextid = iter.index;
133 return rcu_dereference_raw(*slot);
135 EXPORT_SYMBOL(idr_get_next);
138 * idr_replace - replace pointer for given id
140 * @ptr: New pointer to associate with the ID
143 * Replace the pointer registered with an ID and return the old value.
144 * This function can be called under the RCU read lock concurrently with
145 * idr_alloc() and idr_remove() (as long as the ID being removed is not
146 * the one being replaced!).
148 * Returns: 0 on success. %-ENOENT indicates that @id was not found.
149 * %-EINVAL indicates that @id or @ptr were not valid.
151 void *idr_replace(struct idr *idr, void *ptr, int id)
153 struct radix_tree_node *node;
157 if (WARN_ON_ONCE(id < 0))
158 return ERR_PTR(-EINVAL);
159 if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
160 return ERR_PTR(-EINVAL);
162 entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
163 if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
164 return ERR_PTR(-ENOENT);
166 __radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL, NULL);
170 EXPORT_SYMBOL(idr_replace);
173 * DOC: IDA description
175 * The IDA is an ID allocator which does not provide the ability to
176 * associate an ID with a pointer. As such, it only needs to store one
177 * bit per ID, and so is more space efficient than an IDR. To use an IDA,
178 * define it using DEFINE_IDA() (or embed a &struct ida in a data structure,
179 * then initialise it using ida_init()). To allocate a new ID, call
180 * ida_simple_get(). To free an ID, call ida_simple_remove().
182 * If you have more complex locking requirements, use a loop around
183 * ida_pre_get() and ida_get_new() to allocate a new ID. Then use
184 * ida_remove() to free an ID. You must make sure that ida_get_new() and
185 * ida_remove() cannot be called at the same time as each other for the
188 * You can also use ida_get_new_above() if you need an ID to be allocated
189 * above a particular number. ida_destroy() can be used to dispose of an
190 * IDA without needing to free the individual IDs in it. You can use
191 * ida_is_empty() to find out whether the IDA has any IDs currently allocated.
193 * IDs are currently limited to the range [0-INT_MAX]. If this is an awkward
194 * limitation, it should be quite straightforward to raise the maximum.
200 * The IDA uses the functionality provided by the IDR & radix tree to store
201 * bitmaps in each entry. The IDR_FREE tag means there is at least one bit
202 * free, unlike the IDR where it means at least one entry is free.
204 * I considered telling the radix tree that each slot is an order-10 node
205 * and storing the bit numbers in the radix tree, but the radix tree can't
206 * allow a single multiorder entry at index 0, which would significantly
207 * increase memory consumption for the IDA. So instead we divide the index
208 * by the number of bits in the leaf bitmap before doing a radix tree lookup.
210 * As an optimisation, if there are only a few low bits set in any given
211 * leaf, instead of allocating a 128-byte bitmap, we use the 'exceptional
212 * entry' functionality of the radix tree to store BITS_PER_LONG - 2 bits
213 * directly in the entry. By being really tricksy, we could store
214 * BITS_PER_LONG - 1 bits, but there're diminishing returns after optimising
215 * for 0-3 allocated IDs.
217 * We allow the radix tree 'exceptional' count to get out of date. Nothing
218 * in the IDA nor the radix tree code checks it. If it becomes important
219 * to maintain an accurate exceptional count, switch the rcu_assign_pointer()
220 * calls to radix_tree_iter_replace() which will correct the exceptional
223 * The IDA always requires a lock to alloc/free. If we add a 'test_bit'
224 * equivalent, it will still need locking. Going to RCU lookup would require
225 * using RCU to free bitmaps, and that's not trivial without embedding an
226 * RCU head in the bitmap, which adds a 2-pointer overhead to each 128-byte
227 * bitmap, which is excessive.
230 #define IDA_MAX (0x80000000U / IDA_BITMAP_BITS)
233 * ida_get_new_above - allocate new ID above or equal to a start id
235 * @start: id to start search at
236 * @id: pointer to the allocated handle
238 * Allocate new ID above or equal to @start. It should be called
239 * with any required locks to ensure that concurrent calls to
240 * ida_get_new_above() / ida_get_new() / ida_remove() are not allowed.
241 * Consider using ida_simple_get() if you do not have complex locking
244 * If memory is required, it will return %-EAGAIN, you should unlock
245 * and go back to the ida_pre_get() call. If the ida is full, it will
246 * return %-ENOSPC. On success, it will return 0.
248 * @id returns a value in the range @start ... %0x7fffffff.
250 int ida_get_new_above(struct ida *ida, int start, int *id)
252 struct radix_tree_root *root = &ida->ida_rt;
254 struct radix_tree_iter iter;
255 struct ida_bitmap *bitmap;
260 index = start / IDA_BITMAP_BITS;
261 bit = start % IDA_BITMAP_BITS;
262 ebit = bit + RADIX_TREE_EXCEPTIONAL_SHIFT;
264 slot = radix_tree_iter_init(&iter, index);
267 slot = radix_tree_next_slot(slot, &iter,
268 RADIX_TREE_ITER_TAGGED);
270 slot = idr_get_free(root, &iter, GFP_NOWAIT, IDA_MAX);
272 if (slot == ERR_PTR(-ENOMEM))
274 return PTR_ERR(slot);
277 if (iter.index > index) {
279 ebit = RADIX_TREE_EXCEPTIONAL_SHIFT;
281 new = iter.index * IDA_BITMAP_BITS;
282 bitmap = rcu_dereference_raw(*slot);
283 if (radix_tree_exception(bitmap)) {
284 unsigned long tmp = (unsigned long)bitmap;
285 ebit = find_next_zero_bit(&tmp, BITS_PER_LONG, ebit);
286 if (ebit < BITS_PER_LONG) {
288 rcu_assign_pointer(*slot, (void *)tmp);
289 *id = new + ebit - RADIX_TREE_EXCEPTIONAL_SHIFT;
292 bitmap = this_cpu_xchg(ida_bitmap, NULL);
295 memset(bitmap, 0, sizeof(*bitmap));
296 bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
297 rcu_assign_pointer(*slot, bitmap);
301 bit = find_next_zero_bit(bitmap->bitmap,
302 IDA_BITMAP_BITS, bit);
306 if (bit == IDA_BITMAP_BITS)
309 __set_bit(bit, bitmap->bitmap);
310 if (bitmap_full(bitmap->bitmap, IDA_BITMAP_BITS))
311 radix_tree_iter_tag_clear(root, &iter,
317 if (ebit < BITS_PER_LONG) {
318 bitmap = (void *)((1UL << ebit) |
319 RADIX_TREE_EXCEPTIONAL_ENTRY);
320 radix_tree_iter_replace(root, &iter, slot,
325 bitmap = this_cpu_xchg(ida_bitmap, NULL);
328 memset(bitmap, 0, sizeof(*bitmap));
329 __set_bit(bit, bitmap->bitmap);
330 radix_tree_iter_replace(root, &iter, slot, bitmap);
337 EXPORT_SYMBOL(ida_get_new_above);
340 * ida_remove - Free the given ID
344 * This function should not be called at the same time as ida_get_new_above().
346 void ida_remove(struct ida *ida, int id)
348 unsigned long index = id / IDA_BITMAP_BITS;
349 unsigned offset = id % IDA_BITMAP_BITS;
350 struct ida_bitmap *bitmap;
352 struct radix_tree_iter iter;
355 slot = radix_tree_iter_lookup(&ida->ida_rt, &iter, index);
359 bitmap = rcu_dereference_raw(*slot);
360 if (radix_tree_exception(bitmap)) {
361 btmp = (unsigned long *)slot;
362 offset += RADIX_TREE_EXCEPTIONAL_SHIFT;
363 if (offset >= BITS_PER_LONG)
366 btmp = bitmap->bitmap;
368 if (!test_bit(offset, btmp))
371 __clear_bit(offset, btmp);
372 radix_tree_iter_tag_set(&ida->ida_rt, &iter, IDR_FREE);
373 if (radix_tree_exception(bitmap)) {
374 if (rcu_dereference_raw(*slot) ==
375 (void *)RADIX_TREE_EXCEPTIONAL_ENTRY)
376 radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
377 } else if (bitmap_empty(btmp, IDA_BITMAP_BITS)) {
379 radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
383 WARN(1, "ida_remove called for id=%d which is not allocated.\n", id);
385 EXPORT_SYMBOL(ida_remove);
388 * ida_destroy - Free the contents of an ida
391 * Calling this function releases all resources associated with an IDA. When
392 * this call returns, the IDA is empty and can be reused or freed. The caller
393 * should not allow ida_remove() or ida_get_new_above() to be called at the
396 void ida_destroy(struct ida *ida)
398 struct radix_tree_iter iter;
401 radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
402 struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);
403 if (!radix_tree_exception(bitmap))
405 radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
408 EXPORT_SYMBOL(ida_destroy);
411 * ida_simple_get - get a new id.
412 * @ida: the (initialized) ida.
413 * @start: the minimum id (inclusive, < 0x8000000)
414 * @end: the maximum id (exclusive, < 0x8000000 or 0)
415 * @gfp_mask: memory allocation flags
417 * Allocates an id in the range start <= id < end, or returns -ENOSPC.
418 * On memory allocation failure, returns -ENOMEM.
420 * Compared to ida_get_new_above() this function does its own locking, and
421 * should be used unless there are special requirements.
423 * Use ida_simple_remove() to get rid of an id.
425 int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
432 BUG_ON((int)start < 0);
433 BUG_ON((int)end < 0);
443 if (!ida_pre_get(ida, gfp_mask))
446 spin_lock_irqsave(&simple_ida_lock, flags);
447 ret = ida_get_new_above(ida, start, &id);
456 spin_unlock_irqrestore(&simple_ida_lock, flags);
458 if (unlikely(ret == -EAGAIN))
463 EXPORT_SYMBOL(ida_simple_get);
466 * ida_simple_remove - remove an allocated id.
467 * @ida: the (initialized) ida.
468 * @id: the id returned by ida_simple_get.
470 * Use to release an id allocated with ida_simple_get().
472 * Compared to ida_remove() this function does its own locking, and should be
473 * used unless there are special requirements.
475 void ida_simple_remove(struct ida *ida, unsigned int id)
480 spin_lock_irqsave(&simple_ida_lock, flags);
482 spin_unlock_irqrestore(&simple_ida_lock, flags);
484 EXPORT_SYMBOL(ida_simple_remove);