/*
* 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, unsigned 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,
unsigned int element_nr)
{
return element_nr / __elements_per_part(fa->element_size);
}
/**
* flex_array_free_parts - just free the second-level pages
*
* 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 unsigned int index_inside_part(struct flex_array *fa,
unsigned int element_nr)
{
unsigned int part_offset;
part_offset = element_nr % __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) {
/*
* 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, 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_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, 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
* @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)];
}
