Dave Hansen | 534acc0 | 2009-07-29 15:04:18 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Flexible array managed in PAGE_SIZE parts |
| 3 | * |
| 4 | * This program is free software; you can redistribute it and/or modify |
| 5 | * it under the terms of the GNU General Public License as published by |
| 6 | * the Free Software Foundation; either version 2 of the License, or |
| 7 | * (at your option) any later version. |
| 8 | * |
| 9 | * This program is distributed in the hope that it will be useful, |
| 10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 12 | * GNU General Public License for more details. |
| 13 | * |
| 14 | * You should have received a copy of the GNU General Public License |
| 15 | * along with this program; if not, write to the Free Software |
| 16 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 17 | * |
| 18 | * Copyright IBM Corporation, 2009 |
| 19 | * |
| 20 | * Author: Dave Hansen <dave@linux.vnet.ibm.com> |
| 21 | */ |
| 22 | |
| 23 | #include <linux/flex_array.h> |
| 24 | #include <linux/slab.h> |
| 25 | #include <linux/stddef.h> |
| 26 | |
| 27 | struct flex_array_part { |
| 28 | char elements[FLEX_ARRAY_PART_SIZE]; |
| 29 | }; |
| 30 | |
| 31 | static inline int __elements_per_part(int element_size) |
| 32 | { |
| 33 | return FLEX_ARRAY_PART_SIZE / element_size; |
| 34 | } |
| 35 | |
| 36 | static inline int bytes_left_in_base(void) |
| 37 | { |
| 38 | int element_offset = offsetof(struct flex_array, parts); |
| 39 | int bytes_left = FLEX_ARRAY_BASE_SIZE - element_offset; |
| 40 | return bytes_left; |
| 41 | } |
| 42 | |
| 43 | static inline int nr_base_part_ptrs(void) |
| 44 | { |
| 45 | return bytes_left_in_base() / sizeof(struct flex_array_part *); |
| 46 | } |
| 47 | |
| 48 | /* |
| 49 | * If a user requests an allocation which is small |
| 50 | * enough, we may simply use the space in the |
| 51 | * flex_array->parts[] array to store the user |
| 52 | * data. |
| 53 | */ |
| 54 | static inline int elements_fit_in_base(struct flex_array *fa) |
| 55 | { |
| 56 | int data_size = fa->element_size * fa->total_nr_elements; |
| 57 | if (data_size <= bytes_left_in_base()) |
| 58 | return 1; |
| 59 | return 0; |
| 60 | } |
| 61 | |
| 62 | /** |
| 63 | * flex_array_alloc - allocate a new flexible array |
| 64 | * @element_size: the size of individual elements in the array |
| 65 | * @total: total number of elements that this should hold |
| 66 | * |
| 67 | * Note: all locking must be provided by the caller. |
| 68 | * |
| 69 | * @total is used to size internal structures. If the user ever |
| 70 | * accesses any array indexes >=@total, it will produce errors. |
| 71 | * |
| 72 | * The maximum number of elements is defined as: the number of |
| 73 | * elements that can be stored in a page times the number of |
| 74 | * page pointers that we can fit in the base structure or (using |
| 75 | * integer math): |
| 76 | * |
| 77 | * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *) |
| 78 | * |
| 79 | * Here's a table showing example capacities. Note that the maximum |
| 80 | * index that the get/put() functions is just nr_objects-1. This |
| 81 | * basically means that you get 4MB of storage on 32-bit and 2MB on |
| 82 | * 64-bit. |
| 83 | * |
| 84 | * |
| 85 | * Element size | Objects | Objects | |
| 86 | * PAGE_SIZE=4k | 32-bit | 64-bit | |
| 87 | * ---------------------------------| |
| 88 | * 1 bytes | 4186112 | 2093056 | |
| 89 | * 2 bytes | 2093056 | 1046528 | |
| 90 | * 3 bytes | 1395030 | 697515 | |
| 91 | * 4 bytes | 1046528 | 523264 | |
| 92 | * 32 bytes | 130816 | 65408 | |
| 93 | * 33 bytes | 126728 | 63364 | |
| 94 | * 2048 bytes | 2044 | 1022 | |
| 95 | * 2049 bytes | 1022 | 511 | |
| 96 | * void * | 1046528 | 261632 | |
| 97 | * |
| 98 | * Since 64-bit pointers are twice the size, we lose half the |
| 99 | * capacity in the base structure. Also note that no effort is made |
| 100 | * to efficiently pack objects across page boundaries. |
| 101 | */ |
| 102 | struct flex_array *flex_array_alloc(int element_size, int total, gfp_t flags) |
| 103 | { |
| 104 | struct flex_array *ret; |
| 105 | int max_size = nr_base_part_ptrs() * __elements_per_part(element_size); |
| 106 | |
| 107 | /* max_size will end up 0 if element_size > PAGE_SIZE */ |
| 108 | if (total > max_size) |
| 109 | return NULL; |
| 110 | ret = kzalloc(sizeof(struct flex_array), flags); |
| 111 | if (!ret) |
| 112 | return NULL; |
| 113 | ret->element_size = element_size; |
| 114 | ret->total_nr_elements = total; |
| 115 | return ret; |
| 116 | } |
| 117 | |
| 118 | static int fa_element_to_part_nr(struct flex_array *fa, int element_nr) |
| 119 | { |
| 120 | return element_nr / __elements_per_part(fa->element_size); |
| 121 | } |
| 122 | |
| 123 | /** |
| 124 | * flex_array_free_parts - just free the second-level pages |
| 125 | * @src: address of data to copy into the array |
| 126 | * @element_nr: index of the position in which to insert |
| 127 | * the new element. |
| 128 | * |
| 129 | * This is to be used in cases where the base 'struct flex_array' |
| 130 | * has been statically allocated and should not be free. |
| 131 | */ |
| 132 | void flex_array_free_parts(struct flex_array *fa) |
| 133 | { |
| 134 | int part_nr; |
| 135 | int max_part = nr_base_part_ptrs(); |
| 136 | |
| 137 | if (elements_fit_in_base(fa)) |
| 138 | return; |
| 139 | for (part_nr = 0; part_nr < max_part; part_nr++) |
| 140 | kfree(fa->parts[part_nr]); |
| 141 | } |
| 142 | |
| 143 | void flex_array_free(struct flex_array *fa) |
| 144 | { |
| 145 | flex_array_free_parts(fa); |
| 146 | kfree(fa); |
| 147 | } |
| 148 | |
| 149 | static int fa_index_inside_part(struct flex_array *fa, int element_nr) |
| 150 | { |
| 151 | return element_nr % __elements_per_part(fa->element_size); |
| 152 | } |
| 153 | |
| 154 | static int index_inside_part(struct flex_array *fa, int element_nr) |
| 155 | { |
| 156 | int part_offset = fa_index_inside_part(fa, element_nr); |
| 157 | return part_offset * fa->element_size; |
| 158 | } |
| 159 | |
| 160 | static struct flex_array_part * |
| 161 | __fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags) |
| 162 | { |
| 163 | struct flex_array_part *part = fa->parts[part_nr]; |
| 164 | if (!part) { |
| 165 | /* |
| 166 | * This leaves the part pages uninitialized |
| 167 | * and with potentially random data, just |
| 168 | * as if the user had kmalloc()'d the whole. |
| 169 | * __GFP_ZERO can be used to zero it. |
| 170 | */ |
| 171 | part = kmalloc(FLEX_ARRAY_PART_SIZE, flags); |
| 172 | if (!part) |
| 173 | return NULL; |
| 174 | fa->parts[part_nr] = part; |
| 175 | } |
| 176 | return part; |
| 177 | } |
| 178 | |
| 179 | /** |
| 180 | * flex_array_put - copy data into the array at @element_nr |
| 181 | * @src: address of data to copy into the array |
| 182 | * @element_nr: index of the position in which to insert |
| 183 | * the new element. |
| 184 | * |
| 185 | * Note that this *copies* the contents of @src into |
| 186 | * the array. If you are trying to store an array of |
| 187 | * pointers, make sure to pass in &ptr instead of ptr. |
| 188 | * |
| 189 | * Locking must be provided by the caller. |
| 190 | */ |
| 191 | int flex_array_put(struct flex_array *fa, int element_nr, void *src, gfp_t flags) |
| 192 | { |
| 193 | int part_nr = fa_element_to_part_nr(fa, element_nr); |
| 194 | struct flex_array_part *part; |
| 195 | void *dst; |
| 196 | |
| 197 | if (element_nr >= fa->total_nr_elements) |
| 198 | return -ENOSPC; |
| 199 | if (elements_fit_in_base(fa)) |
| 200 | part = (struct flex_array_part *)&fa->parts[0]; |
| 201 | else |
| 202 | part = __fa_get_part(fa, part_nr, flags); |
| 203 | if (!part) |
| 204 | return -ENOMEM; |
| 205 | dst = &part->elements[index_inside_part(fa, element_nr)]; |
| 206 | memcpy(dst, src, fa->element_size); |
| 207 | return 0; |
| 208 | } |
| 209 | |
| 210 | /** |
| 211 | * flex_array_prealloc - guarantee that array space exists |
| 212 | * @start: index of first array element for which space is allocated |
| 213 | * @end: index of last (inclusive) element for which space is allocated |
| 214 | * |
| 215 | * This will guarantee that no future calls to flex_array_put() |
| 216 | * will allocate memory. It can be used if you are expecting to |
| 217 | * be holding a lock or in some atomic context while writing |
| 218 | * data into the array. |
| 219 | * |
| 220 | * Locking must be provided by the caller. |
| 221 | */ |
| 222 | int flex_array_prealloc(struct flex_array *fa, int start, int end, gfp_t flags) |
| 223 | { |
| 224 | int start_part; |
| 225 | int end_part; |
| 226 | int part_nr; |
| 227 | struct flex_array_part *part; |
| 228 | |
| 229 | if (start >= fa->total_nr_elements || end >= fa->total_nr_elements) |
| 230 | return -ENOSPC; |
| 231 | if (elements_fit_in_base(fa)) |
| 232 | return 0; |
| 233 | start_part = fa_element_to_part_nr(fa, start); |
| 234 | end_part = fa_element_to_part_nr(fa, end); |
| 235 | for (part_nr = start_part; part_nr <= end_part; part_nr++) { |
| 236 | part = __fa_get_part(fa, part_nr, flags); |
| 237 | if (!part) |
| 238 | return -ENOMEM; |
| 239 | } |
| 240 | return 0; |
| 241 | } |
| 242 | |
| 243 | /** |
| 244 | * flex_array_get - pull data back out of the array |
| 245 | * @element_nr: index of the element to fetch from the array |
| 246 | * |
| 247 | * Returns a pointer to the data at index @element_nr. Note |
| 248 | * that this is a copy of the data that was passed in. If you |
| 249 | * are using this to store pointers, you'll get back &ptr. |
| 250 | * |
| 251 | * Locking must be provided by the caller. |
| 252 | */ |
| 253 | void *flex_array_get(struct flex_array *fa, int element_nr) |
| 254 | { |
| 255 | int part_nr = fa_element_to_part_nr(fa, element_nr); |
| 256 | struct flex_array_part *part; |
| 257 | int index; |
| 258 | |
| 259 | if (element_nr >= fa->total_nr_elements) |
| 260 | return NULL; |
| 261 | if (!fa->parts[part_nr]) |
| 262 | return NULL; |
| 263 | if (elements_fit_in_base(fa)) |
| 264 | part = (struct flex_array_part *)&fa->parts[0]; |
| 265 | else |
| 266 | part = fa->parts[part_nr]; |
| 267 | index = index_inside_part(fa, element_nr); |
| 268 | return &part->elements[index_inside_part(fa, element_nr)]; |
| 269 | } |