[linux.git] / lib / flex_array.c

/*
 * Flexible array managed in PAGE_SIZE parts
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright IBM Corporation, 2009
 *
 * Author: Dave Hansen <[email protected]>
 */

#include <linux/flex_array.h>
#include <linux/slab.h>
#include <linux/stddef.h>
#include <linux/module.h>

struct flex_array_part {
	char elements[FLEX_ARRAY_PART_SIZE];
};

/*
 * If a user requests an allocation which is small
 * enough, we may simply use the space in the
 * flex_array->parts[] array to store the user
 * data.
 */
static inline int elements_fit_in_base(struct flex_array *fa)
{
	int data_size = fa->element_size * fa->total_nr_elements;
	if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
		return 1;
	return 0;
}

/**
 * flex_array_alloc - allocate a new flexible array
 * @element_size:	the size of individual elements in the array
 * @total:		total number of elements that this should hold
 * @flags:		page allocation flags to use for base array
 *
 * Note: all locking must be provided by the caller.
 *
 * @total is used to size internal structures.  If the user ever
 * accesses any array indexes >=@total, it will produce errors.
 *
 * The maximum number of elements is defined as: the number of
 * elements that can be stored in a page times the number of
 * page pointers that we can fit in the base structure or (using
 * integer math):
 *
 * 	(PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
 *
 * Here's a table showing example capacities.  Note that the maximum
 * index that the get/put() functions is just nr_objects-1.   This
 * basically means that you get 4MB of storage on 32-bit and 2MB on
 * 64-bit.
 *
 *
 * Element size | Objects | Objects |
 * PAGE_SIZE=4k |  32-bit |  64-bit |
 * ---------------------------------|
 *      1 bytes | 4186112 | 2093056 |
 *      2 bytes | 2093056 | 1046528 |
 *      3 bytes | 1395030 |  697515 |
 *      4 bytes | 1046528 |  523264 |
 *     32 bytes |  130816 |   65408 |
 *     33 bytes |  126728 |   63364 |
 *   2048 bytes |    2044 |    1022 |
 *   2049 bytes |    1022 |     511 |
 *       void * | 1046528 |  261632 |
 *
 * Since 64-bit pointers are twice the size, we lose half the
 * capacity in the base structure.  Also note that no effort is made
 * to efficiently pack objects across page boundaries.
 */
struct flex_array *flex_array_alloc(int element_size, unsigned int total,
					gfp_t flags)
{
	struct flex_array *ret;
	int max_size = FLEX_ARRAY_NR_BASE_PTRS *
				FLEX_ARRAY_ELEMENTS_PER_PART(element_size);

	/* max_size will end up 0 if element_size > PAGE_SIZE */
	if (total > max_size)
		return NULL;
	ret = kzalloc(sizeof(struct flex_array), flags);
	if (!ret)
		return NULL;
	ret->element_size = element_size;
	ret->total_nr_elements = total;
	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
		memset(&ret->parts[0], FLEX_ARRAY_FREE,
						FLEX_ARRAY_BASE_BYTES_LEFT);
	return ret;
}
EXPORT_SYMBOL(flex_array_alloc);

static int fa_element_to_part_nr(struct flex_array *fa,
					unsigned int element_nr)
{
	return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
}

/**
 * flex_array_free_parts - just free the second-level pages
 * @fa:		the flex array from which to free parts
 *
 * This is to be used in cases where the base 'struct flex_array'
 * has been statically allocated and should not be free.
 */
void flex_array_free_parts(struct flex_array *fa)
{
	int part_nr;

	if (elements_fit_in_base(fa))
		return;
	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
		kfree(fa->parts[part_nr]);
}
EXPORT_SYMBOL(flex_array_free_parts);

void flex_array_free(struct flex_array *fa)
{
	flex_array_free_parts(fa);
	kfree(fa);
}
EXPORT_SYMBOL(flex_array_free);

static unsigned int index_inside_part(struct flex_array *fa,
					unsigned int element_nr)
{
	unsigned int part_offset;

	part_offset = element_nr %
				FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
	return part_offset * fa->element_size;
}

static struct flex_array_part *
__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
{
	struct flex_array_part *part = fa->parts[part_nr];
	if (!part) {
		part = kmalloc(sizeof(struct flex_array_part), flags);
		if (!part)
			return NULL;
		if (!(flags & __GFP_ZERO))
			memset(part, FLEX_ARRAY_FREE,
				sizeof(struct flex_array_part));
		fa->parts[part_nr] = part;
	}
	return part;
}

/**
 * flex_array_put - copy data into the array at @element_nr
 * @fa:		the flex array to copy data into
 * @element_nr:	index of the position in which to insert
 * 		the new element.
 * @src:	address of data to copy into the array
 * @flags:	page allocation flags to use for array expansion
 *
 *
 * Note that this *copies* the contents of @src into
 * the array.  If you are trying to store an array of
 * pointers, make sure to pass in &ptr instead of ptr.
 * You may instead wish to use the flex_array_put_ptr()
 * helper function.
 *
 * Locking must be provided by the caller.
 */
int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
			gfp_t flags)
{
	int part_nr = fa_element_to_part_nr(fa, element_nr);
	struct flex_array_part *part;
	void *dst;

	if (element_nr >= fa->total_nr_elements)
		return -ENOSPC;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part = __fa_get_part(fa, part_nr, flags);
		if (!part)
			return -ENOMEM;
	}
	dst = &part->elements[index_inside_part(fa, element_nr)];
	memcpy(dst, src, fa->element_size);
	return 0;
}
EXPORT_SYMBOL(flex_array_put);

/**
 * flex_array_clear - clear element in array at @element_nr
 * @fa:		the flex array of the element.
 * @element_nr:	index of the position to clear.
 *
 * Locking must be provided by the caller.
 */
int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
{
	int part_nr = fa_element_to_part_nr(fa, element_nr);
	struct flex_array_part *part;
	void *dst;

	if (element_nr >= fa->total_nr_elements)
		return -ENOSPC;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part = fa->parts[part_nr];
		if (!part)
			return -EINVAL;
	}
	dst = &part->elements[index_inside_part(fa, element_nr)];
	memset(dst, FLEX_ARRAY_FREE, fa->element_size);
	return 0;
}
EXPORT_SYMBOL(flex_array_clear);

/**
 * flex_array_prealloc - guarantee that array space exists
 * @fa:		the flex array for which to preallocate parts
 * @start:	index of first array element for which space is allocated
 * @end:	index of last (inclusive) element for which space is allocated
 * @flags:	page allocation flags
 *
 * This will guarantee that no future calls to flex_array_put()
 * will allocate memory.  It can be used if you are expecting to
 * be holding a lock or in some atomic context while writing
 * data into the array.
 *
 * Locking must be provided by the caller.
 */
int flex_array_prealloc(struct flex_array *fa, unsigned int start,
			unsigned int end, gfp_t flags)
{
	int start_part;
	int end_part;
	int part_nr;
	struct flex_array_part *part;

	if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
		return -ENOSPC;
	if (elements_fit_in_base(fa))
		return 0;
	start_part = fa_element_to_part_nr(fa, start);
	end_part = fa_element_to_part_nr(fa, end);
	for (part_nr = start_part; part_nr <= end_part; part_nr++) {
		part = __fa_get_part(fa, part_nr, flags);
		if (!part)
			return -ENOMEM;
	}
	return 0;
}
EXPORT_SYMBOL(flex_array_prealloc);

/**
 * flex_array_get - pull data back out of the array
 * @fa:		the flex array from which to extract data
 * @element_nr:	index of the element to fetch from the array
 *
 * Returns a pointer to the data at index @element_nr.  Note
 * that this is a copy of the data that was passed in.  If you
 * are using this to store pointers, you'll get back &ptr.  You
 * may instead wish to use the flex_array_get_ptr helper.
 *
 * Locking must be provided by the caller.
 */
void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
{
	int part_nr = fa_element_to_part_nr(fa, element_nr);
	struct flex_array_part *part;

	if (element_nr >= fa->total_nr_elements)
		return NULL;
	if (elements_fit_in_base(fa))
		part = (struct flex_array_part *)&fa->parts[0];
	else {
		part = fa->parts[part_nr];
		if (!part)
			return NULL;
	}
	return &part->elements[index_inside_part(fa, element_nr)];
}
EXPORT_SYMBOL(flex_array_get);

/**
 * flex_array_get_ptr - pull a ptr back out of the array
 * @fa:		the flex array from which to extract data
 * @element_nr:	index of the element to fetch from the array
 *
 * Returns the pointer placed in the flex array at element_nr using
 * flex_array_put_ptr().  This function should not be called if the
 * element in question was not set using the _put_ptr() helper.
 */
void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
{
	void **tmp;

	tmp = flex_array_get(fa, element_nr);
	if (!tmp)
		return NULL;

	return *tmp;
}
EXPORT_SYMBOL(flex_array_get_ptr);

static int part_is_free(struct flex_array_part *part)
{
	int i;

	for (i = 0; i < sizeof(struct flex_array_part); i++)
		if (part->elements[i] != FLEX_ARRAY_FREE)
			return 0;
	return 1;
}

/**
 * flex_array_shrink - free unused second-level pages
 * @fa:		the flex array to shrink
 *
 * Frees all second-level pages that consist solely of unused
 * elements.  Returns the number of pages freed.
 *
 * Locking must be provided by the caller.
 */
int flex_array_shrink(struct flex_array *fa)
{
	struct flex_array_part *part;
	int part_nr;
	int ret = 0;

	if (elements_fit_in_base(fa))
		return ret;
	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
		part = fa->parts[part_nr];
		if (!part)
			continue;
		if (part_is_free(part)) {
			fa->parts[part_nr] = NULL;
			kfree(part);
			ret++;
		}
	}
	return ret;
}
EXPORT_SYMBOL(flex_array_shrink);
Commit	Line	Data
534acc05 DH	1	/*
	2	* Flexible array managed in PAGE_SIZE parts
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License as published by
	6	* the Free Software Foundation; either version 2 of the License, or
	7	* (at your option) any later version.
	8	*
	9	* This program is distributed in the hope that it will be useful,
	10	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	12	* GNU General Public License for more details.
	13	*
	14	* You should have received a copy of the GNU General Public License
	15	* along with this program; if not, write to the Free Software
	16	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	17	*
	18	* Copyright IBM Corporation, 2009
	19	*
	20	* Author: Dave Hansen <[email protected]>
	21	*/
	22
	23	#include <linux/flex_array.h>
	24	#include <linux/slab.h>
	25	#include <linux/stddef.h>
78c377d1	26	#include <linux/module.h>
534acc05 DH	27
	28	struct flex_array_part {
	29	char elements[FLEX_ARRAY_PART_SIZE];
	30	};
	31
534acc05 DH	32	/*
	33	* If a user requests an allocation which is small
	34	* enough, we may simply use the space in the
	35	* flex_array->parts[] array to store the user
	36	* data.
	37	*/
	38	static inline int elements_fit_in_base(struct flex_array *fa)
	39	{
	40	int data_size = fa->element_size * fa->total_nr_elements;
45b588d6	41	if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
534acc05 DH	42	return 1;
	43	return 0;
	44	}
	45
	46	/**
	47	* flex_array_alloc - allocate a new flexible array
	48	* @element_size: the size of individual elements in the array
	49	* @total: total number of elements that this should hold
fc0d8d94	50	* @flags: page allocation flags to use for base array
534acc05 DH	51	*
	52	* Note: all locking must be provided by the caller.
	53	*
	54	* @total is used to size internal structures. If the user ever
	55	* accesses any array indexes >=@total, it will produce errors.
	56	*
	57	* The maximum number of elements is defined as: the number of
	58	* elements that can be stored in a page times the number of
	59	* page pointers that we can fit in the base structure or (using
	60	* integer math):
	61	*
	62	* (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
	63	*
	64	* Here's a table showing example capacities. Note that the maximum
	65	* index that the get/put() functions is just nr_objects-1. This
	66	* basically means that you get 4MB of storage on 32-bit and 2MB on
	67	* 64-bit.
	68	*
	69	*
	70	* Element size \| Objects \| Objects \|
	71	* PAGE_SIZE=4k \| 32-bit \| 64-bit \|
	72	* ---------------------------------\|
	73	* 1 bytes \| 4186112 \| 2093056 \|
	74	* 2 bytes \| 2093056 \| 1046528 \|
	75	* 3 bytes \| 1395030 \| 697515 \|
	76	* 4 bytes \| 1046528 \| 523264 \|
	77	* 32 bytes \| 130816 \| 65408 \|
	78	* 33 bytes \| 126728 \| 63364 \|
	79	* 2048 bytes \| 2044 \| 1022 \|
	80	* 2049 bytes \| 1022 \| 511 \|
	81	* void * \| 1046528 \| 261632 \|
	82	*
	83	* Since 64-bit pointers are twice the size, we lose half the
	84	* capacity in the base structure. Also note that no effort is made
	85	* to efficiently pack objects across page boundaries.
	86	*/
b62e408c DR	87	struct flex_array *flex_array_alloc(int element_size, unsigned int total,
b62e408c DR	88	gfp_t flags)
534acc05 DH	89	{
534acc05 DH	90	struct flex_array *ret;
45b588d6 DR	91	int max_size = FLEX_ARRAY_NR_BASE_PTRS *
45b588d6 DR	92	FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
534acc05 DH	93
	94	/* max_size will end up 0 if element_size > PAGE_SIZE */
	95	if (total > max_size)
	96	return NULL;
	97	ret = kzalloc(sizeof(struct flex_array), flags);
	98	if (!ret)
	99	return NULL;
	100	ret->element_size = element_size;
	101	ret->total_nr_elements = total;
19da3dd1	102	if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
e59464c7	103	memset(&ret->parts[0], FLEX_ARRAY_FREE,
45b588d6	104	FLEX_ARRAY_BASE_BYTES_LEFT);
534acc05 DH	105	return ret;
534acc05 DH	106	}
78c377d1	107	EXPORT_SYMBOL(flex_array_alloc);
534acc05	108
b62e408c DR	109	static int fa_element_to_part_nr(struct flex_array *fa,
b62e408c DR	110	unsigned int element_nr)
534acc05	111	{
45b588d6	112	return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
534acc05 DH	113	}
	114
	115	/**
	116	* flex_array_free_parts - just free the second-level pages
fc0d8d94	117	* @fa: the flex array from which to free parts
534acc05 DH	118	*
	119	* This is to be used in cases where the base 'struct flex_array'
	120	* has been statically allocated and should not be free.
	121	*/
	122	void flex_array_free_parts(struct flex_array *fa)
	123	{
	124	int part_nr;
534acc05 DH	125
	126	if (elements_fit_in_base(fa))
	127	return;
45b588d6	128	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
534acc05 DH	129	kfree(fa->parts[part_nr]);
534acc05 DH	130	}
78c377d1	131	EXPORT_SYMBOL(flex_array_free_parts);
534acc05 DH	132
	133	void flex_array_free(struct flex_array *fa)
	134	{
	135	flex_array_free_parts(fa);
	136	kfree(fa);
	137	}
78c377d1	138	EXPORT_SYMBOL(flex_array_free);
534acc05	139
b62e408c DR	140	static unsigned int index_inside_part(struct flex_array *fa,
b62e408c DR	141	unsigned int element_nr)
534acc05	142	{
b62e408c	143	unsigned int part_offset;
534acc05	144
45b588d6 DR	145	part_offset = element_nr %
45b588d6 DR	146	FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
534acc05 DH	147	return part_offset * fa->element_size;
	148	}
	149
	150	static struct flex_array_part *
	151	__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
	152	{
	153	struct flex_array_part *part = fa->parts[part_nr];
	154	if (!part) {
19da3dd1	155	part = kmalloc(sizeof(struct flex_array_part), flags);
534acc05 DH	156	if (!part)
534acc05 DH	157	return NULL;
19da3dd1 DR	158	if (!(flags & __GFP_ZERO))
	159	memset(part, FLEX_ARRAY_FREE,
	160	sizeof(struct flex_array_part));
534acc05 DH	161	fa->parts[part_nr] = part;
	162	}
	163	return part;
	164	}
	165
	166	/**
	167	* flex_array_put - copy data into the array at @element_nr
fc0d8d94	168	* @fa: the flex array to copy data into
534acc05 DH	169	* @element_nr: index of the position in which to insert
534acc05 DH	170	* the new element.
fc0d8d94 DR	171	* @src: address of data to copy into the array
	172	* @flags: page allocation flags to use for array expansion
	173	*
534acc05 DH	174	*
	175	* Note that this copies the contents of @src into
	176	* the array. If you are trying to store an array of
	177	* pointers, make sure to pass in &ptr instead of ptr.
ea98eed9 EP	178	* You may instead wish to use the flex_array_put_ptr()
ea98eed9 EP	179	* helper function.
534acc05 DH	180	*
	181	* Locking must be provided by the caller.
	182	*/
b62e408c DR	183	int flex_array_put(struct flex_array fa, unsigned int element_nr, void src,
b62e408c DR	184	gfp_t flags)
534acc05 DH	185	{
	186	int part_nr = fa_element_to_part_nr(fa, element_nr);
	187	struct flex_array_part *part;
	188	void *dst;
	189
	190	if (element_nr >= fa->total_nr_elements)
	191	return -ENOSPC;
	192	if (elements_fit_in_base(fa))
	193	part = (struct flex_array_part *)&fa->parts[0];
a30b595d	194	else {
534acc05	195	part = __fa_get_part(fa, part_nr, flags);
a30b595d DR	196	if (!part)
	197	return -ENOMEM;
	198	}
534acc05 DH	199	dst = &part->elements[index_inside_part(fa, element_nr)];
	200	memcpy(dst, src, fa->element_size);
	201	return 0;
	202	}
78c377d1	203	EXPORT_SYMBOL(flex_array_put);
534acc05	204
e6de3988 DR	205	/**
e6de3988 DR	206	* flex_array_clear - clear element in array at @element_nr
fc0d8d94	207	* @fa: the flex array of the element.
e6de3988 DR	208	* @element_nr: index of the position to clear.
	209	*
	210	* Locking must be provided by the caller.
	211	*/
	212	int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
	213	{
	214	int part_nr = fa_element_to_part_nr(fa, element_nr);
	215	struct flex_array_part *part;
	216	void *dst;
	217
	218	if (element_nr >= fa->total_nr_elements)
	219	return -ENOSPC;
	220	if (elements_fit_in_base(fa))
	221	part = (struct flex_array_part *)&fa->parts[0];
	222	else {
	223	part = fa->parts[part_nr];
	224	if (!part)
	225	return -EINVAL;
	226	}
	227	dst = &part->elements[index_inside_part(fa, element_nr)];
19da3dd1	228	memset(dst, FLEX_ARRAY_FREE, fa->element_size);
e6de3988 DR	229	return 0;
e6de3988 DR	230	}
78c377d1	231	EXPORT_SYMBOL(flex_array_clear);
e6de3988	232
534acc05 DH	233	/**
534acc05 DH	234	* flex_array_prealloc - guarantee that array space exists
fc0d8d94	235	* @fa: the flex array for which to preallocate parts
534acc05 DH	236	* @start: index of first array element for which space is allocated
534acc05 DH	237	* @end: index of last (inclusive) element for which space is allocated
fc0d8d94	238	* @flags: page allocation flags
534acc05 DH	239	*
	240	* This will guarantee that no future calls to flex_array_put()
	241	* will allocate memory. It can be used if you are expecting to
	242	* be holding a lock or in some atomic context while writing
	243	* data into the array.
	244	*
	245	* Locking must be provided by the caller.
	246	*/
b62e408c DR	247	int flex_array_prealloc(struct flex_array *fa, unsigned int start,
b62e408c DR	248	unsigned int end, gfp_t flags)
534acc05 DH	249	{
	250	int start_part;
	251	int end_part;
	252	int part_nr;
	253	struct flex_array_part *part;
	254
	255	if (start >= fa->total_nr_elements \|\| end >= fa->total_nr_elements)
	256	return -ENOSPC;
	257	if (elements_fit_in_base(fa))
	258	return 0;
	259	start_part = fa_element_to_part_nr(fa, start);
	260	end_part = fa_element_to_part_nr(fa, end);
	261	for (part_nr = start_part; part_nr <= end_part; part_nr++) {
	262	part = __fa_get_part(fa, part_nr, flags);
	263	if (!part)
	264	return -ENOMEM;
	265	}
	266	return 0;
	267	}
78c377d1	268	EXPORT_SYMBOL(flex_array_prealloc);
534acc05 DH	269
	270	/**
	271	* flex_array_get - pull data back out of the array
fc0d8d94	272	* @fa: the flex array from which to extract data
534acc05 DH	273	* @element_nr: index of the element to fetch from the array
	274	*
	275	* Returns a pointer to the data at index @element_nr. Note
	276	* that this is a copy of the data that was passed in. If you
ea98eed9 EP	277	* are using this to store pointers, you'll get back &ptr. You
ea98eed9 EP	278	* may instead wish to use the flex_array_get_ptr helper.
534acc05 DH	279	*
	280	* Locking must be provided by the caller.
	281	*/
b62e408c	282	void flex_array_get(struct flex_array fa, unsigned int element_nr)
534acc05 DH	283	{
	284	int part_nr = fa_element_to_part_nr(fa, element_nr);
	285	struct flex_array_part *part;
534acc05 DH	286
	287	if (element_nr >= fa->total_nr_elements)
	288	return NULL;
534acc05 DH	289	if (elements_fit_in_base(fa))
534acc05 DH	290	part = (struct flex_array_part *)&fa->parts[0];
a30b595d	291	else {
534acc05	292	part = fa->parts[part_nr];
a30b595d DR	293	if (!part)
	294	return NULL;
	295	}
534acc05 DH	296	return &part->elements[index_inside_part(fa, element_nr)];
534acc05 DH	297	}
78c377d1	298	EXPORT_SYMBOL(flex_array_get);
4af5a2f7	299
ea98eed9 EP	300	/**
	301	* flex_array_get_ptr - pull a ptr back out of the array
	302	* @fa: the flex array from which to extract data
	303	* @element_nr: index of the element to fetch from the array
	304	*
	305	* Returns the pointer placed in the flex array at element_nr using
	306	* flex_array_put_ptr(). This function should not be called if the
	307	* element in question was not set using the _put_ptr() helper.
	308	*/
	309	void flex_array_get_ptr(struct flex_array fa, unsigned int element_nr)
	310	{
	311	void **tmp;
	312
	313	tmp = flex_array_get(fa, element_nr);
	314	if (!tmp)
	315	return NULL;
	316
	317	return *tmp;
	318	}
78c377d1	319	EXPORT_SYMBOL(flex_array_get_ptr);
ea98eed9	320
4af5a2f7 DR	321	static int part_is_free(struct flex_array_part *part)
	322	{
	323	int i;
	324
	325	for (i = 0; i < sizeof(struct flex_array_part); i++)
	326	if (part->elements[i] != FLEX_ARRAY_FREE)
	327	return 0;
	328	return 1;
	329	}
	330
	331	/**
	332	* flex_array_shrink - free unused second-level pages
fc0d8d94	333	* @fa: the flex array to shrink
4af5a2f7 DR	334	*
	335	* Frees all second-level pages that consist solely of unused
	336	* elements. Returns the number of pages freed.
	337	*
	338	* Locking must be provided by the caller.
	339	*/
	340	int flex_array_shrink(struct flex_array *fa)
	341	{
	342	struct flex_array_part *part;
4af5a2f7 DR	343	int part_nr;
	344	int ret = 0;
	345
	346	if (elements_fit_in_base(fa))
	347	return ret;
45b588d6	348	for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
4af5a2f7 DR	349	part = fa->parts[part_nr];
	350	if (!part)
	351	continue;
	352	if (part_is_free(part)) {
	353	fa->parts[part_nr] = NULL;
	354	kfree(part);
	355	ret++;
	356	}
	357	}
	358	return ret;
	359	}
78c377d1	360	EXPORT_SYMBOL(flex_array_shrink);