/*
   * 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];
  };

  /*
   * 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;
  }

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

  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.
   *
   * 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;
  }
  
  /**

   * 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;
  }
  
  /**

   * 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;
  }
  
  /**
   * 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.
   *
   * 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)];
  }

  
  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;
  }