/*
   * 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>
  #include <linux/export.h>
  #include <linux/reciprocal_div.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 | 4177920 | 2088960 |
   *      2 bytes | 2088960 | 1044480 |
   *      3 bytes | 1392300 |  696150 |
   *      4 bytes | 1044480 |  522240 |
   *     32 bytes |  130560 |   65408 |
   *     33 bytes |  126480 |   63240 |
   *   2048 bytes |    2040 |    1020 |
   *   2049 bytes |    1020 |     510 |
   *       void * | 1044480 |  261120 |
   *
   * 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 elems_per_part = 0;
  	int max_size = 0;
  	struct reciprocal_value reciprocal_elems = { 0 };
  
  	if (element_size) {
  		elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
  		reciprocal_elems = reciprocal_value(elems_per_part);
  		max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part;
  	}
  
  	/* 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;
  	ret->elems_per_part = elems_per_part;
  	ret->reciprocal_elems = reciprocal_elems;
  	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)
  {
  	/*
  	 * if element_size == 0 we don't get here, so we never touch
  	 * the zeroed fa->reciprocal_elems, which would yield invalid
  	 * results
  	 */
  	return reciprocal_divide(element_nr, fa->reciprocal_elems);
  }
  
  /**
   * 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_nr)
  {
  	unsigned int part_offset;
  
  	part_offset = element_nr - part_nr * fa->elems_per_part;
  	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 = 0;
  	struct flex_array_part *part;
  	void *dst;
  
  	if (element_nr >= fa->total_nr_elements)
  		return -ENOSPC;
  	if (!fa->element_size)
  		return 0;
  	if (elements_fit_in_base(fa))
  		part = (struct flex_array_part *)&fa->parts[0];
  	else {
  		part_nr = fa_element_to_part_nr(fa, element_nr);
  		part = __fa_get_part(fa, part_nr, flags);
  		if (!part)
  			return -ENOMEM;
  	}
  	dst = &part->elements[index_inside_part(fa, element_nr, part_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 = 0;
  	struct flex_array_part *part;
  	void *dst;
  
  	if (element_nr >= fa->total_nr_elements)
  		return -ENOSPC;
  	if (!fa->element_size)
  		return 0;
  	if (elements_fit_in_base(fa))
  		part = (struct flex_array_part *)&fa->parts[0];
  	else {
  		part_nr = fa_element_to_part_nr(fa, element_nr);
  		part = fa->parts[part_nr];
  		if (!part)
  			return -EINVAL;
  	}
  	dst = &part->elements[index_inside_part(fa, element_nr, part_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
   * @nr_elements:	number of elements 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 nr_elements, gfp_t flags)
  {
  	int start_part;
  	int end_part;
  	int part_nr;
  	unsigned int end;
  	struct flex_array_part *part;
  
  	if (!start && !nr_elements)
  		return 0;
  	if (start >= fa->total_nr_elements)
  		return -ENOSPC;
  	if (!nr_elements)
  		return 0;
  
  	end = start + nr_elements - 1;
  
  	if (end >= fa->total_nr_elements)
  		return -ENOSPC;
  	if (!fa->element_size)
  		return 0;
  	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 = 0;
  	struct flex_array_part *part;
  
  	if (!fa->element_size)
  		return NULL;
  	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_nr = fa_element_to_part_nr(fa, element_nr);
  		part = fa->parts[part_nr];
  		if (!part)
  			return NULL;
  	}
  	return &part->elements[index_inside_part(fa, element_nr, part_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 (!fa->total_nr_elements || !fa->element_size)
  		return 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);