/**
* 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 reciprocal_elems = 0;
int max_size = 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;
}
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 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);
}
