#ifndef _FLEX_ARRAY_H
  #define _FLEX_ARRAY_H
  
  #include <linux/types.h>

  #include <linux/reciprocal_div.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;

  			int elems_per_part;

  			struct reciprocal_value reciprocal_elems;

  			struct flex_array_part *parts[];

  		};
  		/*
  		 * This little trick makes sure that
  		 * sizeof(flex_array) == PAGE_SIZE
  		 */
  		char padding[FLEX_ARRAY_BASE_SIZE];
  	};
  };

  /* Number of bytes left in base struct flex_array, excluding metadata */
  #define FLEX_ARRAY_BASE_BYTES_LEFT					\
  	(FLEX_ARRAY_BASE_SIZE - offsetof(struct flex_array, parts))
  
  /* Number of pointers in base to struct flex_array_part pages */
  #define FLEX_ARRAY_NR_BASE_PTRS						\
  	(FLEX_ARRAY_BASE_BYTES_LEFT / sizeof(struct flex_array_part *))
  
  /* Number of elements of size that fit in struct flex_array_part */
  #define FLEX_ARRAY_ELEMENTS_PER_PART(size)				\
  	(FLEX_ARRAY_PART_SIZE / size)
  
  /*
   * Defines a statically allocated flex array and ensures its parameters are
   * valid.
   */
  #define DEFINE_FLEX_ARRAY(__arrayname, __element_size, __total)		\
  	struct flex_array __arrayname = { { {				\
  		.element_size = (__element_size),			\
  		.total_nr_elements = (__total),				\
  	} } };								\
  	static inline void __arrayname##_invalid_parameter(void)	\
  	{								\
  		BUILD_BUG_ON((__total) > FLEX_ARRAY_NR_BASE_PTRS *	\
  			FLEX_ARRAY_ELEMENTS_PER_PART(__element_size));	\
  	}

  struct flex_array *flex_array_alloc(int element_size, unsigned int total,
  		gfp_t flags);
  int flex_array_prealloc(struct flex_array *fa, unsigned int start,

  		unsigned int nr_elements, 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, unsigned int element_nr, void *src,

  		gfp_t flags);

  int flex_array_clear(struct flex_array *fa, unsigned int element_nr);

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

  int flex_array_shrink(struct flex_array *fa);

  #define flex_array_put_ptr(fa, nr, src, gfp) \

  	flex_array_put(fa, nr, (void *)&(src), gfp)

  
  void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr);

  #endif /* _FLEX_ARRAY_H */