[net-next-2.6.git] / lib / idr.c

/*
 * 2002-10-18  written by Jim Houston jim.houston@ccur.com
 *	Copyright (C) 2002 by Concurrent Computer Corporation
 *	Distributed under the GNU GPL license version 2.
 *
 * Modified by George Anzinger to reuse immediately and to use
 * find bit instructions.  Also removed _irq on spinlocks.
 *
 * Small id to pointer translation service.
 *
 * It uses a radix tree like structure as a sparse array indexed
 * by the id to obtain the pointer.  The bitmap makes allocating
 * a new id quick.
 *
 * You call it to allocate an id (an int) an associate with that id a
 * pointer or what ever, we treat it as a (void *).  You can pass this
 * id to a user for him to pass back at a later time.  You then pass
 * that id to this code and it returns your pointer.

 * You can release ids at any time. When all ids are released, most of
 * the memory is returned (we keep IDR_FREE_MAX) in a local pool so we
 * don't need to go to the memory "store" during an id allocate, just
 * so you don't need to be too concerned about locking and conflicts
 * with the slab allocator.
 */

#ifndef TEST                        // to test in user space...
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/module.h>
#endif
#include <linux/string.h>
#include <linux/idr.h>

static kmem_cache_t *idr_layer_cache;

static struct idr_layer *alloc_layer(struct idr *idp)
{
	struct idr_layer *p;

	spin_lock(&idp->lock);
	if ((p = idp->id_free)) {
		idp->id_free = p->ary[0];
		idp->id_free_cnt--;
		p->ary[0] = NULL;
	}
	spin_unlock(&idp->lock);
	return(p);
}

static void free_layer(struct idr *idp, struct idr_layer *p)
{
	/*
	 * Depends on the return element being zeroed.
	 */
	spin_lock(&idp->lock);
	p->ary[0] = idp->id_free;
	idp->id_free = p;
	idp->id_free_cnt++;
	spin_unlock(&idp->lock);
}

/**
 * idr_pre_get - reserver resources for idr allocation
 * @idp:	idr handle
 * @gfp_mask:	memory allocation flags
 *
 * This function should be called prior to locking and calling the
 * following function.  It preallocates enough memory to satisfy
 * the worst possible allocation.
 *
 * If the system is REALLY out of memory this function returns 0,
 * otherwise 1.
 */
int idr_pre_get(struct idr *idp, gfp_t gfp_mask)
{
	while (idp->id_free_cnt < IDR_FREE_MAX) {
		struct idr_layer *new;
		new = kmem_cache_alloc(idr_layer_cache, gfp_mask);
		if (new == NULL)
			return (0);
		free_layer(idp, new);
	}
	return 1;
}
EXPORT_SYMBOL(idr_pre_get);

static int sub_alloc(struct idr *idp, void *ptr, int *starting_id)
{
	int n, m, sh;
	struct idr_layer *p, *new;
	struct idr_layer *pa[MAX_LEVEL];
	int l, id;
	long bm;

	id = *starting_id;
	p = idp->top;
	l = idp->layers;
	pa[l--] = NULL;
	while (1) {
		/*
		 * We run around this while until we reach the leaf node...
		 */
		n = (id >> (IDR_BITS*l)) & IDR_MASK;
		bm = ~p->bitmap;
		m = find_next_bit(&bm, IDR_SIZE, n);
		if (m == IDR_SIZE) {
			/* no space available go back to previous layer. */
			l++;
			id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;
			if (!(p = pa[l])) {
				*starting_id = id;
				return -2;
			}
			continue;
		}
		if (m != n) {
			sh = IDR_BITS*l;
			id = ((id >> sh) ^ n ^ m) << sh;
		}
		if ((id >= MAX_ID_BIT) || (id < 0))
			return -3;
		if (l == 0)
			break;
		/*
		 * Create the layer below if it is missing.
		 */
		if (!p->ary[m]) {
			if (!(new = alloc_layer(idp)))
				return -1;
			p->ary[m] = new;
			p->count++;
		}
		pa[l--] = p;
		p = p->ary[m];
	}
	/*
	 * We have reached the leaf node, plant the
	 * users pointer and return the raw id.
	 */
	p->ary[m] = (struct idr_layer *)ptr;
	__set_bit(m, &p->bitmap);
	p->count++;
	/*
	 * If this layer is full mark the bit in the layer above
	 * to show that this part of the radix tree is full.
	 * This may complete the layer above and require walking
	 * up the radix tree.
	 */
	n = id;
	while (p->bitmap == IDR_FULL) {
		if (!(p = pa[++l]))
			break;
		n = n >> IDR_BITS;
		__set_bit((n & IDR_MASK), &p->bitmap);
	}
	return(id);
}

static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
{
	struct idr_layer *p, *new;
	int layers, v, id;

	id = starting_id;
build_up:
	p = idp->top;
	layers = idp->layers;
	if (unlikely(!p)) {
		if (!(p = alloc_layer(idp)))
			return -1;
		layers = 1;
	}
	/*
	 * Add a new layer to the top of the tree if the requested
	 * id is larger than the currently allocated space.
	 */
	while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
		layers++;
		if (!p->count)
			continue;
		if (!(new = alloc_layer(idp))) {
			/*
			 * The allocation failed.  If we built part of
			 * the structure tear it down.
			 */
			for (new = p; p && p != idp->top; new = p) {
				p = p->ary[0];
				new->ary[0] = NULL;
				new->bitmap = new->count = 0;
				free_layer(idp, new);
			}
			return -1;
		}
		new->ary[0] = p;
		new->count = 1;
		if (p->bitmap == IDR_FULL)
			__set_bit(0, &new->bitmap);
		p = new;
	}
	idp->top = p;
	idp->layers = layers;
	v = sub_alloc(idp, ptr, &id);
	if (v == -2)
		goto build_up;
	return(v);
}

/**
 * idr_get_new_above - allocate new idr entry above or equal to a start id
 * @idp: idr handle
 * @ptr: pointer you want associated with the ide
 * @start_id: id to start search at
 * @id: pointer to the allocated handle
 *
 * This is the allocate id function.  It should be called with any
 * required locks.
 *
 * If memory is required, it will return -EAGAIN, you should unlock
 * and go back to the idr_pre_get() call.  If the idr is full, it will
 * return -ENOSPC.
 *
 * @id returns a value in the range 0 ... 0x7fffffff
 */
int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
{
	int rv;

	rv = idr_get_new_above_int(idp, ptr, starting_id);
	/*
	 * This is a cheap hack until the IDR code can be fixed to
	 * return proper error values.
	 */
	if (rv < 0) {
		if (rv == -1)
			return -EAGAIN;
		else /* Will be -3 */
			return -ENOSPC;
	}
	*id = rv;
	return 0;
}
EXPORT_SYMBOL(idr_get_new_above);

/**
 * idr_get_new - allocate new idr entry
 * @idp: idr handle
 * @ptr: pointer you want associated with the ide
 * @id: pointer to the allocated handle
 *
 * This is the allocate id function.  It should be called with any
 * required locks.
 *
 * If memory is required, it will return -EAGAIN, you should unlock
 * and go back to the idr_pre_get() call.  If the idr is full, it will
 * return -ENOSPC.
 *
 * @id returns a value in the range 0 ... 0x7fffffff
 */
int idr_get_new(struct idr *idp, void *ptr, int *id)
{
	int rv;

	rv = idr_get_new_above_int(idp, ptr, 0);
	/*
	 * This is a cheap hack until the IDR code can be fixed to
	 * return proper error values.
	 */
	if (rv < 0) {
		if (rv == -1)
			return -EAGAIN;
		else /* Will be -3 */
			return -ENOSPC;
	}
	*id = rv;
	return 0;
}
EXPORT_SYMBOL(idr_get_new);

static void idr_remove_warning(int id)
{
	printk("idr_remove called for id=%d which is not allocated.\n", id);
	dump_stack();
}

static void sub_remove(struct idr *idp, int shift, int id)
{
	struct idr_layer *p = idp->top;
	struct idr_layer **pa[MAX_LEVEL];
	struct idr_layer ***paa = &pa[0];
	int n;

	*paa = NULL;
	*++paa = &idp->top;

	while ((shift > 0) && p) {
		n = (id >> shift) & IDR_MASK;
		__clear_bit(n, &p->bitmap);
		*++paa = &p->ary[n];
		p = p->ary[n];
		shift -= IDR_BITS;
	}
	n = id & IDR_MASK;
	if (likely(p != NULL && test_bit(n, &p->bitmap))){
		__clear_bit(n, &p->bitmap);
		p->ary[n] = NULL;
		while(*paa && ! --((**paa)->count)){
			free_layer(idp, **paa);
			**paa-- = NULL;
		}
		if (!*paa)
			idp->layers = 0;
	} else
		idr_remove_warning(id);
}

/**
 * idr_remove - remove the given id and free it's slot
 * idp: idr handle
 * id: uniqueue key
 */
void idr_remove(struct idr *idp, int id)
{
	struct idr_layer *p;

	/* Mask off upper bits we don't use for the search. */
	id &= MAX_ID_MASK;

	sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
	if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
	    idp->top->ary[0]) {  // We can drop a layer

		p = idp->top->ary[0];
		idp->top->bitmap = idp->top->count = 0;
		free_layer(idp, idp->top);
		idp->top = p;
		--idp->layers;
	}
	while (idp->id_free_cnt >= IDR_FREE_MAX) {
		p = alloc_layer(idp);
		kmem_cache_free(idr_layer_cache, p);
		return;
	}
}
EXPORT_SYMBOL(idr_remove);

/**
 * idr_destroy - release all cached layers within an idr tree
 * idp: idr handle
 */
void idr_destroy(struct idr *idp)
{
	while (idp->id_free_cnt) {
		struct idr_layer *p = alloc_layer(idp);
		kmem_cache_free(idr_layer_cache, p);
	}
}
EXPORT_SYMBOL(idr_destroy);

/**
 * idr_find - return pointer for given id
 * @idp: idr handle
 * @id: lookup key
 *
 * Return the pointer given the id it has been registered with.  A %NULL
 * return indicates that @id is not valid or you passed %NULL in
 * idr_get_new().
 *
 * The caller must serialize idr_find() vs idr_get_new() and idr_remove().
 */
void *idr_find(struct idr *idp, int id)
{
	int n;
	struct idr_layer *p;

	n = idp->layers * IDR_BITS;
	p = idp->top;

	/* Mask off upper bits we don't use for the search. */
	id &= MAX_ID_MASK;

	if (id >= (1 << n))
		return NULL;

	while (n > 0 && p) {
		n -= IDR_BITS;
		p = p->ary[(id >> n) & IDR_MASK];
	}
	return((void *)p);
}
EXPORT_SYMBOL(idr_find);

static void idr_cache_ctor(void * idr_layer, kmem_cache_t *idr_layer_cache,
		unsigned long flags)
{
	memset(idr_layer, 0, sizeof(struct idr_layer));
}

static  int init_id_cache(void)
{
	if (!idr_layer_cache)
		idr_layer_cache = kmem_cache_create("idr_layer_cache",
			sizeof(struct idr_layer), 0, 0, idr_cache_ctor, NULL);
	return 0;
}

/**
 * idr_init - initialize idr handle
 * @idp:	idr handle
 *
 * This function is use to set up the handle (@idp) that you will pass
 * to the rest of the functions.
 */
void idr_init(struct idr *idp)
{
	init_id_cache();
	memset(idp, 0, sizeof(struct idr));
	spin_lock_init(&idp->lock);
}
EXPORT_SYMBOL(idr_init);
Commit	Line	Data
1da177e4 LT	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	*
e15ae2dd	9	* Small id to pointer translation service.
1da177e4	10	*
e15ae2dd	11	* It uses a radix tree like structure as a sparse array indexed
1da177e4	12	* by the id to obtain the pointer. The bitmap makes allocating
e15ae2dd	13	* a new id quick.
1da177e4 LT	14	*
	15	* You call it to allocate an id (an int) an associate with that id a
	16	* pointer or what ever, we treat it as a (void *). You can pass this
	17	* id to a user for him to pass back at a later time. You then pass
	18	* that id to this code and it returns your pointer.
	19
e15ae2dd	20	* You can release ids at any time. When all ids are released, most of
1da177e4	21	* the memory is returned (we keep IDR_FREE_MAX) in a local pool so we
e15ae2dd	22	* don't need to go to the memory "store" during an id allocate, just
1da177e4 LT	23	* so you don't need to be too concerned about locking and conflicts
	24	* with the slab allocator.
	25	*/
	26
	27	#ifndef TEST // to test in user space...
	28	#include <linux/slab.h>
	29	#include <linux/init.h>
	30	#include <linux/module.h>
	31	#endif
	32	#include <linux/string.h>
	33	#include <linux/idr.h>
	34
	35	static kmem_cache_t *idr_layer_cache;
	36
	37	static struct idr_layer alloc_layer(struct idr idp)
	38	{
	39	struct idr_layer *p;
	40
	41	spin_lock(&idp->lock);
	42	if ((p = idp->id_free)) {
	43	idp->id_free = p->ary[0];
	44	idp->id_free_cnt--;
	45	p->ary[0] = NULL;
	46	}
	47	spin_unlock(&idp->lock);
	48	return(p);
	49	}
	50
	51	static void free_layer(struct idr idp, struct idr_layer p)
	52	{
	53	/*
	54	* Depends on the return element being zeroed.
	55	*/
	56	spin_lock(&idp->lock);
	57	p->ary[0] = idp->id_free;
	58	idp->id_free = p;
	59	idp->id_free_cnt++;
	60	spin_unlock(&idp->lock);
	61	}
	62
	63	/**
	64	* idr_pre_get - reserver resources for idr allocation
	65	* @idp: idr handle
	66	* @gfp_mask: memory allocation flags
	67	*
	68	* This function should be called prior to locking and calling the
	69	* following function. It preallocates enough memory to satisfy
	70	* the worst possible allocation.
	71	*
	72	* If the system is REALLY out of memory this function returns 0,
	73	* otherwise 1.
	74	*/
fd4f2df2	75	int idr_pre_get(struct idr *idp, gfp_t gfp_mask)
1da177e4 LT	76	{
	77	while (idp->id_free_cnt < IDR_FREE_MAX) {
	78	struct idr_layer *new;
	79	new = kmem_cache_alloc(idr_layer_cache, gfp_mask);
e15ae2dd	80	if (new == NULL)
1da177e4 LT	81	return (0);
	82	free_layer(idp, new);
	83	}
	84	return 1;
	85	}
	86	EXPORT_SYMBOL(idr_pre_get);
	87
	88	static int sub_alloc(struct idr idp, void ptr, int *starting_id)
	89	{
	90	int n, m, sh;
	91	struct idr_layer p, new;
	92	struct idr_layer *pa[MAX_LEVEL];
	93	int l, id;
	94	long bm;
	95
	96	id = *starting_id;
	97	p = idp->top;
	98	l = idp->layers;
	99	pa[l--] = NULL;
	100	while (1) {
	101	/*
	102	* We run around this while until we reach the leaf node...
	103	*/
	104	n = (id >> (IDR_BITS*l)) & IDR_MASK;
	105	bm = ~p->bitmap;
	106	m = find_next_bit(&bm, IDR_SIZE, n);
	107	if (m == IDR_SIZE) {
	108	/* no space available go back to previous layer. */
	109	l++;
e15ae2dd	110	id = (id \| ((1 << (IDR_BITS * l)) - 1)) + 1;
1da177e4 LT	111	if (!(p = pa[l])) {
	112	*starting_id = id;
	113	return -2;
	114	}
	115	continue;
	116	}
	117	if (m != n) {
	118	sh = IDR_BITS*l;
	119	id = ((id >> sh) ^ n ^ m) << sh;
	120	}
	121	if ((id >= MAX_ID_BIT) \|\| (id < 0))
	122	return -3;
	123	if (l == 0)
	124	break;
	125	/*
	126	* Create the layer below if it is missing.
	127	*/
	128	if (!p->ary[m]) {
	129	if (!(new = alloc_layer(idp)))
	130	return -1;
	131	p->ary[m] = new;
	132	p->count++;
	133	}
	134	pa[l--] = p;
	135	p = p->ary[m];
	136	}
	137	/*
	138	* We have reached the leaf node, plant the
	139	* users pointer and return the raw id.
	140	*/
	141	p->ary[m] = (struct idr_layer *)ptr;
	142	__set_bit(m, &p->bitmap);
	143	p->count++;
	144	/*
	145	* If this layer is full mark the bit in the layer above
	146	* to show that this part of the radix tree is full.
	147	* This may complete the layer above and require walking
	148	* up the radix tree.
	149	*/
	150	n = id;
	151	while (p->bitmap == IDR_FULL) {
	152	if (!(p = pa[++l]))
	153	break;
	154	n = n >> IDR_BITS;
	155	__set_bit((n & IDR_MASK), &p->bitmap);
	156	}
	157	return(id);
	158	}
	159
	160	static int idr_get_new_above_int(struct idr idp, void ptr, int starting_id)
	161	{
	162	struct idr_layer p, new;
	163	int layers, v, id;
e15ae2dd	164
1da177e4 LT	165	id = starting_id;
	166	build_up:
	167	p = idp->top;
	168	layers = idp->layers;
	169	if (unlikely(!p)) {
	170	if (!(p = alloc_layer(idp)))
	171	return -1;
	172	layers = 1;
	173	}
	174	/*
	175	* Add a new layer to the top of the tree if the requested
	176	* id is larger than the currently allocated space.
	177	*/
589777ea	178	while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
1da177e4 LT	179	layers++;
	180	if (!p->count)
	181	continue;
	182	if (!(new = alloc_layer(idp))) {
	183	/*
	184	* The allocation failed. If we built part of
	185	* the structure tear it down.
	186	*/
	187	for (new = p; p && p != idp->top; new = p) {
	188	p = p->ary[0];
	189	new->ary[0] = NULL;
	190	new->bitmap = new->count = 0;
	191	free_layer(idp, new);
	192	}
	193	return -1;
	194	}
	195	new->ary[0] = p;
	196	new->count = 1;
	197	if (p->bitmap == IDR_FULL)
	198	__set_bit(0, &new->bitmap);
	199	p = new;
	200	}
	201	idp->top = p;
	202	idp->layers = layers;
	203	v = sub_alloc(idp, ptr, &id);
	204	if (v == -2)
	205	goto build_up;
	206	return(v);
	207	}
	208
	209	/**
7c657f2f	210	* idr_get_new_above - allocate new idr entry above or equal to a start id
1da177e4 LT	211	* @idp: idr handle
	212	* @ptr: pointer you want associated with the ide
	213	* @start_id: id to start search at
	214	* @id: pointer to the allocated handle
	215	*
	216	* This is the allocate id function. It should be called with any
	217	* required locks.
	218	*
	219	* If memory is required, it will return -EAGAIN, you should unlock
	220	* and go back to the idr_pre_get() call. If the idr is full, it will
	221	* return -ENOSPC.
	222	*
	223	* @id returns a value in the range 0 ... 0x7fffffff
	224	*/
	225	int idr_get_new_above(struct idr idp, void ptr, int starting_id, int *id)
	226	{
	227	int rv;
e15ae2dd	228
1da177e4 LT	229	rv = idr_get_new_above_int(idp, ptr, starting_id);
	230	/*
	231	* This is a cheap hack until the IDR code can be fixed to
	232	* return proper error values.
	233	*/
	234	if (rv < 0) {
	235	if (rv == -1)
	236	return -EAGAIN;
	237	else /* Will be -3 */
	238	return -ENOSPC;
	239	}
	240	*id = rv;
	241	return 0;
	242	}
	243	EXPORT_SYMBOL(idr_get_new_above);
	244
	245	/**
	246	* idr_get_new - allocate new idr entry
	247	* @idp: idr handle
	248	* @ptr: pointer you want associated with the ide
	249	* @id: pointer to the allocated handle
	250	*
	251	* This is the allocate id function. It should be called with any
	252	* required locks.
	253	*
	254	* If memory is required, it will return -EAGAIN, you should unlock
	255	* and go back to the idr_pre_get() call. If the idr is full, it will
	256	* return -ENOSPC.
	257	*
	258	* @id returns a value in the range 0 ... 0x7fffffff
	259	*/
	260	int idr_get_new(struct idr idp, void ptr, int *id)
	261	{
	262	int rv;
e15ae2dd	263
1da177e4 LT	264	rv = idr_get_new_above_int(idp, ptr, 0);
	265	/*
	266	* This is a cheap hack until the IDR code can be fixed to
	267	* return proper error values.
	268	*/
	269	if (rv < 0) {
	270	if (rv == -1)
	271	return -EAGAIN;
	272	else /* Will be -3 */
	273	return -ENOSPC;
	274	}
	275	*id = rv;
	276	return 0;
	277	}
	278	EXPORT_SYMBOL(idr_get_new);
	279
	280	static void idr_remove_warning(int id)
	281	{
	282	printk("idr_remove called for id=%d which is not allocated.\n", id);
	283	dump_stack();
	284	}
	285
	286	static void sub_remove(struct idr *idp, int shift, int id)
	287	{
	288	struct idr_layer *p = idp->top;
	289	struct idr_layer **pa[MAX_LEVEL];
	290	struct idr_layer ***paa = &pa[0];
	291	int n;
	292
	293	*paa = NULL;
	294	*++paa = &idp->top;
	295
	296	while ((shift > 0) && p) {
	297	n = (id >> shift) & IDR_MASK;
	298	__clear_bit(n, &p->bitmap);
	299	*++paa = &p->ary[n];
	300	p = p->ary[n];
	301	shift -= IDR_BITS;
	302	}
	303	n = id & IDR_MASK;
	304	if (likely(p != NULL && test_bit(n, &p->bitmap))){
	305	__clear_bit(n, &p->bitmap);
	306	p->ary[n] = NULL;
	307	while(paa && ! --((*paa)->count)){
	308	free_layer(idp, **paa);
	309	**paa-- = NULL;
	310	}
e15ae2dd	311	if (!*paa)
1da177e4	312	idp->layers = 0;
e15ae2dd	313	} else
1da177e4	314	idr_remove_warning(id);
1da177e4 LT	315	}
	316
	317	/**
	318	* idr_remove - remove the given id and free it's slot
	319	* idp: idr handle
	320	* id: uniqueue key
	321	*/
	322	void idr_remove(struct idr *idp, int id)
	323	{
	324	struct idr_layer *p;
	325
	326	/* Mask off upper bits we don't use for the search. */
	327	id &= MAX_ID_MASK;
	328
	329	sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
e15ae2dd JJ	330	if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
e15ae2dd JJ	331	idp->top->ary[0]) { // We can drop a layer
1da177e4 LT	332
	333	p = idp->top->ary[0];
	334	idp->top->bitmap = idp->top->count = 0;
	335	free_layer(idp, idp->top);
	336	idp->top = p;
	337	--idp->layers;
	338	}
	339	while (idp->id_free_cnt >= IDR_FREE_MAX) {
1da177e4 LT	340	p = alloc_layer(idp);
	341	kmem_cache_free(idr_layer_cache, p);
	342	return;
	343	}
	344	}
	345	EXPORT_SYMBOL(idr_remove);
	346
8d3b3591 AM	347	/**
	348	* idr_destroy - release all cached layers within an idr tree
	349	* idp: idr handle
	350	*/
	351	void idr_destroy(struct idr *idp)
	352	{
	353	while (idp->id_free_cnt) {
	354	struct idr_layer *p = alloc_layer(idp);
	355	kmem_cache_free(idr_layer_cache, p);
	356	}
	357	}
	358	EXPORT_SYMBOL(idr_destroy);
	359
1da177e4 LT	360	/**
	361	* idr_find - return pointer for given id
	362	* @idp: idr handle
	363	* @id: lookup key
	364	*
	365	* Return the pointer given the id it has been registered with. A %NULL
	366	* return indicates that @id is not valid or you passed %NULL in
	367	* idr_get_new().
	368	*
	369	* The caller must serialize idr_find() vs idr_get_new() and idr_remove().
	370	*/
	371	void idr_find(struct idr idp, int id)
	372	{
	373	int n;
	374	struct idr_layer *p;
	375
	376	n = idp->layers * IDR_BITS;
	377	p = idp->top;
	378
	379	/* Mask off upper bits we don't use for the search. */
	380	id &= MAX_ID_MASK;
	381
	382	if (id >= (1 << n))
	383	return NULL;
	384
	385	while (n > 0 && p) {
	386	n -= IDR_BITS;
	387	p = p->ary[(id >> n) & IDR_MASK];
	388	}
	389	return((void *)p);
	390	}
	391	EXPORT_SYMBOL(idr_find);
	392
e15ae2dd JJ	393	static void idr_cache_ctor(void * idr_layer, kmem_cache_t *idr_layer_cache,
e15ae2dd JJ	394	unsigned long flags)
1da177e4 LT	395	{
	396	memset(idr_layer, 0, sizeof(struct idr_layer));
	397	}
	398
	399	static int init_id_cache(void)
	400	{
	401	if (!idr_layer_cache)
e15ae2dd	402	idr_layer_cache = kmem_cache_create("idr_layer_cache",
1da177e4 LT	403	sizeof(struct idr_layer), 0, 0, idr_cache_ctor, NULL);
	404	return 0;
	405	}
	406
	407	/**
	408	* idr_init - initialize idr handle
	409	* @idp: idr handle
	410	*
	411	* This function is use to set up the handle (@idp) that you will pass
	412	* to the rest of the functions.
	413	*/
	414	void idr_init(struct idr *idp)
	415	{
	416	init_id_cache();
	417	memset(idp, 0, sizeof(struct idr));
	418	spin_lock_init(&idp->lock);
	419	}
	420	EXPORT_SYMBOL(idr_init);