lib: flexible array implementation

#ifndef _FLEX_ARRAY_H

#define _FLEX_ARRAY_H

#include <linux/types.h>

#include <asm/page.h>

#define FLEX_ARRAY_PART_SIZE PAGE_SIZE

#define FLEX_ARRAY_BASE_SIZE PAGE_SIZE

struct flex_array_part;

/*

 * This is meant to replace cases where an array-like

 * structure has gotten too big to fit into kmalloc()

 * and the developer is getting tempted to use

 * vmalloc().

 */

struct flex_array {

	union {

		struct {

			int element_size;

			int total_nr_elements;

			struct flex_array_part *parts[0];

		};

		/*

		 * This little trick makes sure that

		 * sizeof(flex_array) == PAGE_SIZE

		 */

		char padding[FLEX_ARRAY_BASE_SIZE];

	};

};

#define FLEX_ARRAY_INIT(size, total) { { {\

	.element_size = (size),		\

	.total_nr_elements = (total),	\

} } }

struct flex_array *flex_array_alloc(int element_size, int total, gfp_t flags);

int flex_array_prealloc(struct flex_array *fa, int start, int end, gfp_t flags);

void flex_array_free(struct flex_array *fa);

void flex_array_free_parts(struct flex_array *fa);

int flex_array_put(struct flex_array *fa, int element_nr, void *src,

		gfp_t flags);

void *flex_array_get(struct flex_array *fa, int element_nr);

#endif /* _FLEX_ARRAY_H */

	 idr.o int_sqrt.o extable.o prio_tree.o \

	 sha1.o irq_regs.o reciprocal_div.o argv_split.o \

	 proportions.o prio_heap.o ratelimit.o show_mem.o \

	 is_single_threaded.o plist.o decompress.o

	 is_single_threaded.o plist.o decompress.o flex_array.o

lib-$(CONFIG_MMU) += ioremap.o

lib-$(CONFIG_SMP) += cpumask.o

/*

 * 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 <dave@linux.vnet.ibm.com>

 */

#include <linux/flex_array.h>

#include <linux/slab.h>

#include <linux/stddef.h>

struct flex_array_part {

	char elements[FLEX_ARRAY_PART_SIZE];

};

static inline int __elements_per_part(int element_size)

{

	return FLEX_ARRAY_PART_SIZE / element_size;

}

static inline int bytes_left_in_base(void)

{

	int element_offset = offsetof(struct flex_array, parts);

	int bytes_left = FLEX_ARRAY_BASE_SIZE - element_offset;

	return bytes_left;

}

static inline int nr_base_part_ptrs(void)

{

	return bytes_left_in_base() / sizeof(struct flex_array_part *);

}

/*

 * 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 <= bytes_left_in_base())

		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

 *

 * 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, int total, gfp_t flags)

{

	struct flex_array *ret;

	int max_size = nr_base_part_ptrs() * __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;

	return ret;

}

static int fa_element_to_part_nr(struct flex_array *fa, int element_nr)

{

	return element_nr / __elements_per_part(fa->element_size);

}

/**

 * flex_array_free_parts - just free the second-level pages

 * @src:	address of data to copy into the array

 * @element_nr:	index of the position in which to insert

 * 		the new element.

 *

 * 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;

	int max_part = nr_base_part_ptrs();

	if (elements_fit_in_base(fa))

		return;

	for (part_nr = 0; part_nr < max_part; part_nr++)

		kfree(fa->parts[part_nr]);

}

void flex_array_free(struct flex_array *fa)

{

	flex_array_free_parts(fa);

	kfree(fa);

}

static int fa_index_inside_part(struct flex_array *fa, int element_nr)

{

	return element_nr % __elements_per_part(fa->element_size);

}

static int index_inside_part(struct flex_array *fa, int element_nr)

{

	int part_offset = fa_index_inside_part(fa, element_nr);

	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) {

		/*

		 * This leaves the part pages uninitialized

		 * and with potentially random data, just

		 * as if the user had kmalloc()'d the whole.

		 * __GFP_ZERO can be used to zero it.

		 */

		part = kmalloc(FLEX_ARRAY_PART_SIZE, flags);

		if (!part)

			return NULL;

		fa->parts[part_nr] = part;

	}

	return part;

}

/**

 * flex_array_put - copy data into the array at @element_nr

 * @src:	address of data to copy into the array

 * @element_nr:	index of the position in which to insert

 * 		the new element.

 *

 * 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.

 *

 * Locking must be provided by the caller.

 */

int flex_array_put(struct flex_array *fa, 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;

}

/**

 * flex_array_prealloc - guarantee that array space exists

 * @start:	index of first array element for which space is allocated

 * @end:	index of last (inclusive) element for which space is allocated

 *

 * 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, int start, 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;

}

/**

 * flex_array_get - pull data back out of the array

 * @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.

 *

 * Locking must be provided by the caller.

 */

void *flex_array_get(struct flex_array *fa, int element_nr)

{

	int part_nr = fa_element_to_part_nr(fa, element_nr);

	struct flex_array_part *part;

	int index;

	if (element_nr >= fa->total_nr_elements)

		return NULL;

	if (!fa->parts[part_nr])

		return NULL;

	if (elements_fit_in_base(fa))

		part = (struct flex_array_part *)&fa->parts[0];

	else

		part = fa->parts[part_nr];

	index = index_inside_part(fa, element_nr);

	return &part->elements[index_inside_part(fa, element_nr)];

}