373 lines
10 KiB
C
373 lines
10 KiB
C
/*
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* Flexible array managed in PAGE_SIZE parts
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright IBM Corporation, 2009
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*
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* Author: Dave Hansen <dave@linux.vnet.ibm.com>
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*/
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#include <linux/flex_array.h>
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#include <linux/slab.h>
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#include <linux/stddef.h>
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#include <linux/module.h>
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struct flex_array_part {
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char elements[FLEX_ARRAY_PART_SIZE];
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};
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/*
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* If a user requests an allocation which is small
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* enough, we may simply use the space in the
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* flex_array->parts[] array to store the user
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* data.
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*/
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static inline int elements_fit_in_base(struct flex_array *fa)
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{
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int data_size = fa->element_size * fa->total_nr_elements;
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if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
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return 1;
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return 0;
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}
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/**
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* flex_array_alloc - allocate a new flexible array
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* @element_size: the size of individual elements in the array
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* @total: total number of elements that this should hold
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* @flags: page allocation flags to use for base array
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*
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* Note: all locking must be provided by the caller.
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*
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* @total is used to size internal structures. If the user ever
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* accesses any array indexes >=@total, it will produce errors.
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*
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* The maximum number of elements is defined as: the number of
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* elements that can be stored in a page times the number of
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* page pointers that we can fit in the base structure or (using
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* integer math):
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*
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* (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
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*
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* Here's a table showing example capacities. Note that the maximum
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* index that the get/put() functions is just nr_objects-1. This
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* basically means that you get 4MB of storage on 32-bit and 2MB on
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* 64-bit.
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*
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*
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* Element size | Objects | Objects |
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* PAGE_SIZE=4k | 32-bit | 64-bit |
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* ---------------------------------|
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* 1 bytes | 4186112 | 2093056 |
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* 2 bytes | 2093056 | 1046528 |
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* 3 bytes | 1395030 | 697515 |
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* 4 bytes | 1046528 | 523264 |
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* 32 bytes | 130816 | 65408 |
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* 33 bytes | 126728 | 63364 |
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* 2048 bytes | 2044 | 1022 |
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* 2049 bytes | 1022 | 511 |
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* void * | 1046528 | 261632 |
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*
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* Since 64-bit pointers are twice the size, we lose half the
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* capacity in the base structure. Also note that no effort is made
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* to efficiently pack objects across page boundaries.
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*/
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struct flex_array *flex_array_alloc(int element_size, unsigned int total,
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gfp_t flags)
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{
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struct flex_array *ret;
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int max_size = FLEX_ARRAY_NR_BASE_PTRS *
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FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
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/* max_size will end up 0 if element_size > PAGE_SIZE */
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if (total > max_size)
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return NULL;
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ret = kzalloc(sizeof(struct flex_array), flags);
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if (!ret)
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return NULL;
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ret->element_size = element_size;
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ret->total_nr_elements = total;
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if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
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memset(&ret->parts[0], FLEX_ARRAY_FREE,
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FLEX_ARRAY_BASE_BYTES_LEFT);
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return ret;
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}
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EXPORT_SYMBOL(flex_array_alloc);
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static int fa_element_to_part_nr(struct flex_array *fa,
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unsigned int element_nr)
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{
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return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
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}
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/**
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* flex_array_free_parts - just free the second-level pages
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* @fa: the flex array from which to free parts
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*
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* This is to be used in cases where the base 'struct flex_array'
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* has been statically allocated and should not be free.
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*/
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void flex_array_free_parts(struct flex_array *fa)
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{
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int part_nr;
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if (elements_fit_in_base(fa))
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return;
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for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
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kfree(fa->parts[part_nr]);
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}
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EXPORT_SYMBOL(flex_array_free_parts);
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void flex_array_free(struct flex_array *fa)
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{
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flex_array_free_parts(fa);
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kfree(fa);
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}
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EXPORT_SYMBOL(flex_array_free);
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static unsigned int index_inside_part(struct flex_array *fa,
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unsigned int element_nr)
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{
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unsigned int part_offset;
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part_offset = element_nr %
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FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
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return part_offset * fa->element_size;
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}
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static struct flex_array_part *
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__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
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{
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struct flex_array_part *part = fa->parts[part_nr];
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if (!part) {
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part = kmalloc(sizeof(struct flex_array_part), flags);
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if (!part)
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return NULL;
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if (!(flags & __GFP_ZERO))
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memset(part, FLEX_ARRAY_FREE,
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sizeof(struct flex_array_part));
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fa->parts[part_nr] = part;
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}
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return part;
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}
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/**
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* flex_array_put - copy data into the array at @element_nr
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* @fa: the flex array to copy data into
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* @element_nr: index of the position in which to insert
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* the new element.
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* @src: address of data to copy into the array
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* @flags: page allocation flags to use for array expansion
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*
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*
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* Note that this *copies* the contents of @src into
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* the array. If you are trying to store an array of
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* pointers, make sure to pass in &ptr instead of ptr.
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* You may instead wish to use the flex_array_put_ptr()
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* helper function.
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*
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* Locking must be provided by the caller.
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*/
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int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
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gfp_t flags)
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{
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int part_nr = fa_element_to_part_nr(fa, element_nr);
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struct flex_array_part *part;
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void *dst;
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if (element_nr >= fa->total_nr_elements)
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return -ENOSPC;
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if (elements_fit_in_base(fa))
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part = (struct flex_array_part *)&fa->parts[0];
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else {
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part = __fa_get_part(fa, part_nr, flags);
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if (!part)
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return -ENOMEM;
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}
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dst = &part->elements[index_inside_part(fa, element_nr)];
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memcpy(dst, src, fa->element_size);
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return 0;
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}
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EXPORT_SYMBOL(flex_array_put);
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/**
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* flex_array_clear - clear element in array at @element_nr
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* @fa: the flex array of the element.
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* @element_nr: index of the position to clear.
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*
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* Locking must be provided by the caller.
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*/
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int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
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{
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int part_nr = fa_element_to_part_nr(fa, element_nr);
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struct flex_array_part *part;
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void *dst;
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if (element_nr >= fa->total_nr_elements)
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return -ENOSPC;
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if (elements_fit_in_base(fa))
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part = (struct flex_array_part *)&fa->parts[0];
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else {
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part = fa->parts[part_nr];
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if (!part)
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return -EINVAL;
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}
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dst = &part->elements[index_inside_part(fa, element_nr)];
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memset(dst, FLEX_ARRAY_FREE, fa->element_size);
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return 0;
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}
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EXPORT_SYMBOL(flex_array_clear);
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/**
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* flex_array_prealloc - guarantee that array space exists
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* @fa: the flex array for which to preallocate parts
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* @start: index of first array element for which space is allocated
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* @nr_elements: number of elements for which space is allocated
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* @flags: page allocation flags
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*
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* This will guarantee that no future calls to flex_array_put()
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* will allocate memory. It can be used if you are expecting to
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* be holding a lock or in some atomic context while writing
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* data into the array.
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*
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* Locking must be provided by the caller.
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*/
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int flex_array_prealloc(struct flex_array *fa, unsigned int start,
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unsigned int nr_elements, gfp_t flags)
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{
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int start_part;
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int end_part;
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int part_nr;
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unsigned int end;
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struct flex_array_part *part;
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if (!start && !nr_elements)
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return 0;
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if (start >= fa->total_nr_elements)
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return -ENOSPC;
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if (!nr_elements)
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return 0;
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end = start + nr_elements - 1;
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if (end >= fa->total_nr_elements)
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return -ENOSPC;
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if (elements_fit_in_base(fa))
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return 0;
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start_part = fa_element_to_part_nr(fa, start);
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end_part = fa_element_to_part_nr(fa, end);
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for (part_nr = start_part; part_nr <= end_part; part_nr++) {
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part = __fa_get_part(fa, part_nr, flags);
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if (!part)
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return -ENOMEM;
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}
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return 0;
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}
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EXPORT_SYMBOL(flex_array_prealloc);
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/**
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* flex_array_get - pull data back out of the array
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* @fa: the flex array from which to extract data
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* @element_nr: index of the element to fetch from the array
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*
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* Returns a pointer to the data at index @element_nr. Note
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* that this is a copy of the data that was passed in. If you
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* are using this to store pointers, you'll get back &ptr. You
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* may instead wish to use the flex_array_get_ptr helper.
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*
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* Locking must be provided by the caller.
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*/
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void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
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{
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int part_nr = fa_element_to_part_nr(fa, element_nr);
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struct flex_array_part *part;
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if (element_nr >= fa->total_nr_elements)
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return NULL;
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if (elements_fit_in_base(fa))
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part = (struct flex_array_part *)&fa->parts[0];
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else {
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part = fa->parts[part_nr];
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if (!part)
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return NULL;
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}
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return &part->elements[index_inside_part(fa, element_nr)];
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}
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EXPORT_SYMBOL(flex_array_get);
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/**
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* flex_array_get_ptr - pull a ptr back out of the array
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* @fa: the flex array from which to extract data
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* @element_nr: index of the element to fetch from the array
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*
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* Returns the pointer placed in the flex array at element_nr using
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* flex_array_put_ptr(). This function should not be called if the
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* element in question was not set using the _put_ptr() helper.
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*/
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void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
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{
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void **tmp;
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tmp = flex_array_get(fa, element_nr);
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if (!tmp)
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return NULL;
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return *tmp;
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}
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EXPORT_SYMBOL(flex_array_get_ptr);
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static int part_is_free(struct flex_array_part *part)
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{
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int i;
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for (i = 0; i < sizeof(struct flex_array_part); i++)
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if (part->elements[i] != FLEX_ARRAY_FREE)
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return 0;
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return 1;
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}
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/**
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* flex_array_shrink - free unused second-level pages
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* @fa: the flex array to shrink
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*
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* Frees all second-level pages that consist solely of unused
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* elements. Returns the number of pages freed.
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*
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* Locking must be provided by the caller.
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*/
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int flex_array_shrink(struct flex_array *fa)
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{
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struct flex_array_part *part;
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int part_nr;
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int ret = 0;
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if (!fa->total_nr_elements)
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return 0;
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if (elements_fit_in_base(fa))
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return ret;
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for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
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part = fa->parts[part_nr];
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if (!part)
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continue;
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if (part_is_free(part)) {
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fa->parts[part_nr] = NULL;
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kfree(part);
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ret++;
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}
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}
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return ret;
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}
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EXPORT_SYMBOL(flex_array_shrink);
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