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