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 27struct flex_array_part { 28 char elements[FLEX_ARRAY_PART_SIZE]; 29}; 30 31/* 32 * If a user requests an allocation which is small 33 * enough, we may simply use the space in the 34 * flex_array->parts[] array to store the user 35 * data. 36 */ 37static inline int elements_fit_in_base(struct flex_array *fa) 38{ 39 int data_size = fa->element_size * fa->total_nr_elements; 40 if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT) 41 return 1; 42 return 0; 43} 44 45/** 46 * flex_array_alloc - allocate a new flexible array 47 * @element_size: the size of individual elements in the array 48 * @total: total number of elements that this should hold 49 * @flags: page allocation flags to use for base array 50 * 51 * Note: all locking must be provided by the caller. 52 * 53 * @total is used to size internal structures. If the user ever 54 * accesses any array indexes >=@total, it will produce errors. 55 * 56 * The maximum number of elements is defined as: the number of 57 * elements that can be stored in a page times the number of 58 * page pointers that we can fit in the base structure or (using 59 * integer math): 60 * 61 * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *) 62 * 63 * Here's a table showing example capacities. Note that the maximum 64 * index that the get/put() functions is just nr_objects-1. This 65 * basically means that you get 4MB of storage on 32-bit and 2MB on 66 * 64-bit. 67 * 68 * 69 * Element size | Objects | Objects | 70 * PAGE_SIZE=4k | 32-bit | 64-bit | 71 * ---------------------------------| 72 * 1 bytes | 4186112 | 2093056 | 73 * 2 bytes | 2093056 | 1046528 | 74 * 3 bytes | 1395030 | 697515 | 75 * 4 bytes | 1046528 | 523264 | 76 * 32 bytes | 130816 | 65408 | 77 * 33 bytes | 126728 | 63364 | 78 * 2048 bytes | 2044 | 1022 | 79 * 2049 bytes | 1022 | 511 | 80 * void * | 1046528 | 261632 | 81 * 82 * Since 64-bit pointers are twice the size, we lose half the 83 * capacity in the base structure. Also note that no effort is made 84 * to efficiently pack objects across page boundaries. 85 */ 86struct flex_array *flex_array_alloc(int element_size, unsigned int total, 87 gfp_t flags) 88{ 89 struct flex_array *ret; 90 int max_size = FLEX_ARRAY_NR_BASE_PTRS * 91 FLEX_ARRAY_ELEMENTS_PER_PART(element_size); 92 93 /* max_size will end up 0 if element_size > PAGE_SIZE */ 94 if (total > max_size) 95 return NULL; 96 ret = kzalloc(sizeof(struct flex_array), flags); 97 if (!ret) 98 return NULL; 99 ret->element_size = element_size; 100 ret->total_nr_elements = total; 101 if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO)) 102 memset(&ret->parts[0], FLEX_ARRAY_FREE, 103 FLEX_ARRAY_BASE_BYTES_LEFT); 104 return ret; 105} 106 107static int fa_element_to_part_nr(struct flex_array *fa, 108 unsigned int element_nr) 109{ 110 return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size); 111} 112 113/** 114 * flex_array_free_parts - just free the second-level pages 115 * @fa: the flex array from which to free parts 116 * 117 * This is to be used in cases where the base 'struct flex_array' 118 * has been statically allocated and should not be free. 119 */ 120void flex_array_free_parts(struct flex_array *fa) 121{ 122 int part_nr; 123 124 if (elements_fit_in_base(fa)) 125 return; 126 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) 127 kfree(fa->parts[part_nr]); 128} 129 130void flex_array_free(struct flex_array *fa) 131{ 132 flex_array_free_parts(fa); 133 kfree(fa); 134} 135 136static unsigned int index_inside_part(struct flex_array *fa, 137 unsigned int element_nr) 138{ 139 unsigned int part_offset; 140 141 part_offset = element_nr % 142 FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size); 143 return part_offset * fa->element_size; 144} 145 146static struct flex_array_part * 147__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags) 148{ 149 struct flex_array_part *part = fa->parts[part_nr]; 150 if (!part) { 151 part = kmalloc(sizeof(struct flex_array_part), flags); 152 if (!part) 153 return NULL; 154 if (!(flags & __GFP_ZERO)) 155 memset(part, FLEX_ARRAY_FREE, 156 sizeof(struct flex_array_part)); 157 fa->parts[part_nr] = part; 158 } 159 return part; 160} 161 162/** 163 * flex_array_put - copy data into the array at @element_nr 164 * @fa: the flex array to copy data into 165 * @element_nr: index of the position in which to insert 166 * the new element. 167 * @src: address of data to copy into the array 168 * @flags: page allocation flags to use for array expansion 169 * 170 * 171 * Note that this *copies* the contents of @src into 172 * the array. If you are trying to store an array of 173 * pointers, make sure to pass in &ptr instead of ptr. 174 * You may instead wish to use the flex_array_put_ptr() 175 * helper function. 176 * 177 * Locking must be provided by the caller. 178 */ 179int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src, 180 gfp_t flags) 181{ 182 int part_nr = fa_element_to_part_nr(fa, element_nr); 183 struct flex_array_part *part; 184 void *dst; 185 186 if (element_nr >= fa->total_nr_elements) 187 return -ENOSPC; 188 if (elements_fit_in_base(fa)) 189 part = (struct flex_array_part *)&fa->parts[0]; 190 else { 191 part = __fa_get_part(fa, part_nr, flags); 192 if (!part) 193 return -ENOMEM; 194 } 195 dst = &part->elements[index_inside_part(fa, element_nr)]; 196 memcpy(dst, src, fa->element_size); 197 return 0; 198} 199 200/** 201 * flex_array_clear - clear element in array at @element_nr 202 * @fa: the flex array of the element. 203 * @element_nr: index of the position to clear. 204 * 205 * Locking must be provided by the caller. 206 */ 207int flex_array_clear(struct flex_array *fa, unsigned int element_nr) 208{ 209 int part_nr = fa_element_to_part_nr(fa, element_nr); 210 struct flex_array_part *part; 211 void *dst; 212 213 if (element_nr >= fa->total_nr_elements) 214 return -ENOSPC; 215 if (elements_fit_in_base(fa)) 216 part = (struct flex_array_part *)&fa->parts[0]; 217 else { 218 part = fa->parts[part_nr]; 219 if (!part) 220 return -EINVAL; 221 } 222 dst = &part->elements[index_inside_part(fa, element_nr)]; 223 memset(dst, FLEX_ARRAY_FREE, fa->element_size); 224 return 0; 225} 226 227/** 228 * flex_array_prealloc - guarantee that array space exists 229 * @fa: the flex array for which to preallocate parts 230 * @start: index of first array element for which space is allocated 231 * @end: index of last (inclusive) element for which space is allocated 232 * @flags: page allocation flags 233 * 234 * This will guarantee that no future calls to flex_array_put() 235 * will allocate memory. It can be used if you are expecting to 236 * be holding a lock or in some atomic context while writing 237 * data into the array. 238 * 239 * Locking must be provided by the caller. 240 */ 241int flex_array_prealloc(struct flex_array *fa, unsigned int start, 242 unsigned int end, gfp_t flags) 243{ 244 int start_part; 245 int end_part; 246 int part_nr; 247 struct flex_array_part *part; 248 249 if (start >= fa->total_nr_elements || end >= fa->total_nr_elements) 250 return -ENOSPC; 251 if (elements_fit_in_base(fa)) 252 return 0; 253 start_part = fa_element_to_part_nr(fa, start); 254 end_part = fa_element_to_part_nr(fa, end); 255 for (part_nr = start_part; part_nr <= end_part; part_nr++) { 256 part = __fa_get_part(fa, part_nr, flags); 257 if (!part) 258 return -ENOMEM; 259 } 260 return 0; 261} 262 263/** 264 * flex_array_get - pull data back out of the array 265 * @fa: the flex array from which to extract data 266 * @element_nr: index of the element to fetch from the array 267 * 268 * Returns a pointer to the data at index @element_nr. Note 269 * that this is a copy of the data that was passed in. If you 270 * are using this to store pointers, you'll get back &ptr. You 271 * may instead wish to use the flex_array_get_ptr helper. 272 * 273 * Locking must be provided by the caller. 274 */ 275void *flex_array_get(struct flex_array *fa, unsigned int element_nr) 276{ 277 int part_nr = fa_element_to_part_nr(fa, element_nr); 278 struct flex_array_part *part; 279 280 if (element_nr >= fa->total_nr_elements) 281 return NULL; 282 if (elements_fit_in_base(fa)) 283 part = (struct flex_array_part *)&fa->parts[0]; 284 else { 285 part = fa->parts[part_nr]; 286 if (!part) 287 return NULL; 288 } 289 return &part->elements[index_inside_part(fa, element_nr)]; 290} 291 292/** 293 * flex_array_get_ptr - pull a ptr back out of the array 294 * @fa: the flex array from which to extract data 295 * @element_nr: index of the element to fetch from the array 296 * 297 * Returns the pointer placed in the flex array at element_nr using 298 * flex_array_put_ptr(). This function should not be called if the 299 * element in question was not set using the _put_ptr() helper. 300 */ 301void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr) 302{ 303 void **tmp; 304 305 tmp = flex_array_get(fa, element_nr); 306 if (!tmp) 307 return NULL; 308 309 return *tmp; 310} 311 312static int part_is_free(struct flex_array_part *part) 313{ 314 int i; 315 316 for (i = 0; i < sizeof(struct flex_array_part); i++) 317 if (part->elements[i] != FLEX_ARRAY_FREE) 318 return 0; 319 return 1; 320} 321 322/** 323 * flex_array_shrink - free unused second-level pages 324 * @fa: the flex array to shrink 325 * 326 * Frees all second-level pages that consist solely of unused 327 * elements. Returns the number of pages freed. 328 * 329 * Locking must be provided by the caller. 330 */ 331int flex_array_shrink(struct flex_array *fa) 332{ 333 struct flex_array_part *part; 334 int part_nr; 335 int ret = 0; 336 337 if (elements_fit_in_base(fa)) 338 return ret; 339 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) { 340 part = fa->parts[part_nr]; 341 if (!part) 342 continue; 343 if (part_is_free(part)) { 344 fa->parts[part_nr] = NULL; 345 kfree(part); 346 ret++; 347 } 348 } 349 return ret; 350} 351