/* * 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)]; }