Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/lib/flex_array.c
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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 #include <linux/export.h> 27 #include <linux/reciprocal_div.h> 28 29 struct flex_array_part { 30 char elements[FLEX_ARRAY_PART_SIZE]; 31 }; 32 33 /* 34 * If a user requests an allocation which is small 35 * enough, we may simply use the space in the 36 * flex_array->parts[] array to store the user 37 * data. 38 */ 39 static inline int elements_fit_in_base(struct flex_array *fa) 40 { 41 int data_size = fa->element_size * fa->total_nr_elements; 42 if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT) 43 return 1; 44 return 0; 45 } 46 47 /** 48 * flex_array_alloc - allocate a new flexible array 49 * @element_size: the size of individual elements in the array 50 * @total: total number of elements that this should hold 51 * @flags: page allocation flags to use for base array 52 * 53 * Note: all locking must be provided by the caller. 54 * 55 * @total is used to size internal structures. If the user ever 56 * accesses any array indexes >=@total, it will produce errors. 57 * 58 * The maximum number of elements is defined as: the number of 59 * elements that can be stored in a page times the number of 60 * page pointers that we can fit in the base structure or (using 61 * integer math): 62 * 63 * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *) 64 * 65 * Here's a table showing example capacities. Note that the maximum 66 * index that the get/put() functions is just nr_objects-1. This 67 * basically means that you get 4MB of storage on 32-bit and 2MB on 68 * 64-bit. 69 * 70 * 71 * Element size | Objects | Objects | 72 * PAGE_SIZE=4k | 32-bit | 64-bit | 73 * ---------------------------------| 74 * 1 bytes | 4177920 | 2088960 | 75 * 2 bytes | 2088960 | 1044480 | 76 * 3 bytes | 1392300 | 696150 | 77 * 4 bytes | 1044480 | 522240 | 78 * 32 bytes | 130560 | 65408 | 79 * 33 bytes | 126480 | 63240 | 80 * 2048 bytes | 2040 | 1020 | 81 * 2049 bytes | 1020 | 510 | 82 * void * | 1044480 | 261120 | 83 * 84 * Since 64-bit pointers are twice the size, we lose half the 85 * capacity in the base structure. Also note that no effort is made 86 * to efficiently pack objects across page boundaries. 87 */ 88 struct flex_array *flex_array_alloc(int element_size, unsigned int total, 89 gfp_t flags) 90 { 91 struct flex_array *ret; 92 int elems_per_part = 0; 93 int reciprocal_elems = 0; 94 int max_size = 0; 95 96 if (element_size) { 97 elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size); 98 reciprocal_elems = reciprocal_value(elems_per_part); 99 max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part; 100 } 101 102 /* max_size will end up 0 if element_size > PAGE_SIZE */ 103 if (total > max_size) 104 return NULL; 105 ret = kzalloc(sizeof(struct flex_array), flags); 106 if (!ret) 107 return NULL; 108 ret->element_size = element_size; 109 ret->total_nr_elements = total; 110 ret->elems_per_part = elems_per_part; 111 ret->reciprocal_elems = reciprocal_elems; 112 if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO)) 113 memset(&ret->parts[0], FLEX_ARRAY_FREE, 114 FLEX_ARRAY_BASE_BYTES_LEFT); 115 return ret; 116 } 117 EXPORT_SYMBOL(flex_array_alloc); 118 119 static int fa_element_to_part_nr(struct flex_array *fa, 120 unsigned int element_nr) 121 { 122 return reciprocal_divide(element_nr, fa->reciprocal_elems); 123 } 124 125 /** 126 * flex_array_free_parts - just free the second-level pages 127 * @fa: the flex array from which to free parts 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; 135 136 if (elements_fit_in_base(fa)) 137 return; 138 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) 139 kfree(fa->parts[part_nr]); 140 } 141 EXPORT_SYMBOL(flex_array_free_parts); 142 143 void flex_array_free(struct flex_array *fa) 144 { 145 flex_array_free_parts(fa); 146 kfree(fa); 147 } 148 EXPORT_SYMBOL(flex_array_free); 149 150 static unsigned int index_inside_part(struct flex_array *fa, 151 unsigned int element_nr, 152 unsigned int part_nr) 153 { 154 unsigned int part_offset; 155 156 part_offset = element_nr - part_nr * fa->elems_per_part; 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 part = kmalloc(sizeof(struct flex_array_part), flags); 166 if (!part) 167 return NULL; 168 if (!(flags & __GFP_ZERO)) 169 memset(part, FLEX_ARRAY_FREE, 170 sizeof(struct flex_array_part)); 171 fa->parts[part_nr] = part; 172 } 173 return part; 174 } 175 176 /** 177 * flex_array_put - copy data into the array at @element_nr 178 * @fa: the flex array to copy data into 179 * @element_nr: index of the position in which to insert 180 * the new element. 181 * @src: address of data to copy into the array 182 * @flags: page allocation flags to use for array expansion 183 * 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 * You may instead wish to use the flex_array_put_ptr() 189 * helper function. 190 * 191 * Locking must be provided by the caller. 192 */ 193 int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src, 194 gfp_t flags) 195 { 196 int part_nr = 0; 197 struct flex_array_part *part; 198 void *dst; 199 200 if (element_nr >= fa->total_nr_elements) 201 return -ENOSPC; 202 if (!fa->element_size) 203 return 0; 204 if (elements_fit_in_base(fa)) 205 part = (struct flex_array_part *)&fa->parts[0]; 206 else { 207 part_nr = fa_element_to_part_nr(fa, element_nr); 208 part = __fa_get_part(fa, part_nr, flags); 209 if (!part) 210 return -ENOMEM; 211 } 212 dst = &part->elements[index_inside_part(fa, element_nr, part_nr)]; 213 memcpy(dst, src, fa->element_size); 214 return 0; 215 } 216 EXPORT_SYMBOL(flex_array_put); 217 218 /** 219 * flex_array_clear - clear element in array at @element_nr 220 * @fa: the flex array of the element. 221 * @element_nr: index of the position to clear. 222 * 223 * Locking must be provided by the caller. 224 */ 225 int flex_array_clear(struct flex_array *fa, unsigned int element_nr) 226 { 227 int part_nr = 0; 228 struct flex_array_part *part; 229 void *dst; 230 231 if (element_nr >= fa->total_nr_elements) 232 return -ENOSPC; 233 if (!fa->element_size) 234 return 0; 235 if (elements_fit_in_base(fa)) 236 part = (struct flex_array_part *)&fa->parts[0]; 237 else { 238 part_nr = fa_element_to_part_nr(fa, element_nr); 239 part = fa->parts[part_nr]; 240 if (!part) 241 return -EINVAL; 242 } 243 dst = &part->elements[index_inside_part(fa, element_nr, part_nr)]; 244 memset(dst, FLEX_ARRAY_FREE, fa->element_size); 245 return 0; 246 } 247 EXPORT_SYMBOL(flex_array_clear); 248 249 /** 250 * flex_array_prealloc - guarantee that array space exists 251 * @fa: the flex array for which to preallocate parts 252 * @start: index of first array element for which space is allocated 253 * @nr_elements: number of elements for which space is allocated 254 * @flags: page allocation flags 255 * 256 * This will guarantee that no future calls to flex_array_put() 257 * will allocate memory. It can be used if you are expecting to 258 * be holding a lock or in some atomic context while writing 259 * data into the array. 260 * 261 * Locking must be provided by the caller. 262 */ 263 int flex_array_prealloc(struct flex_array *fa, unsigned int start, 264 unsigned int nr_elements, gfp_t flags) 265 { 266 int start_part; 267 int end_part; 268 int part_nr; 269 unsigned int end; 270 struct flex_array_part *part; 271 272 if (!start && !nr_elements) 273 return 0; 274 if (start >= fa->total_nr_elements) 275 return -ENOSPC; 276 if (!nr_elements) 277 return 0; 278 279 end = start + nr_elements - 1; 280 281 if (end >= fa->total_nr_elements) 282 return -ENOSPC; 283 if (!fa->element_size) 284 return 0; 285 if (elements_fit_in_base(fa)) 286 return 0; 287 start_part = fa_element_to_part_nr(fa, start); 288 end_part = fa_element_to_part_nr(fa, end); 289 for (part_nr = start_part; part_nr <= end_part; part_nr++) { 290 part = __fa_get_part(fa, part_nr, flags); 291 if (!part) 292 return -ENOMEM; 293 } 294 return 0; 295 } 296 EXPORT_SYMBOL(flex_array_prealloc); 297 298 /** 299 * flex_array_get - pull data back out of the array 300 * @fa: the flex array from which to extract data 301 * @element_nr: index of the element to fetch from the array 302 * 303 * Returns a pointer to the data at index @element_nr. Note 304 * that this is a copy of the data that was passed in. If you 305 * are using this to store pointers, you'll get back &ptr. You 306 * may instead wish to use the flex_array_get_ptr helper. 307 * 308 * Locking must be provided by the caller. 309 */ 310 void *flex_array_get(struct flex_array *fa, unsigned int element_nr) 311 { 312 int part_nr = 0; 313 struct flex_array_part *part; 314 315 if (!fa->element_size) 316 return NULL; 317 if (element_nr >= fa->total_nr_elements) 318 return NULL; 319 if (elements_fit_in_base(fa)) 320 part = (struct flex_array_part *)&fa->parts[0]; 321 else { 322 part_nr = fa_element_to_part_nr(fa, element_nr); 323 part = fa->parts[part_nr]; 324 if (!part) 325 return NULL; 326 } 327 return &part->elements[index_inside_part(fa, element_nr, part_nr)]; 328 } 329 EXPORT_SYMBOL(flex_array_get); 330 331 /** 332 * flex_array_get_ptr - pull a ptr back out of the array 333 * @fa: the flex array from which to extract data 334 * @element_nr: index of the element to fetch from the array 335 * 336 * Returns the pointer placed in the flex array at element_nr using 337 * flex_array_put_ptr(). This function should not be called if the 338 * element in question was not set using the _put_ptr() helper. 339 */ 340 void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr) 341 { 342 void **tmp; 343 344 tmp = flex_array_get(fa, element_nr); 345 if (!tmp) 346 return NULL; 347 348 return *tmp; 349 } 350 EXPORT_SYMBOL(flex_array_get_ptr); 351 352 static int part_is_free(struct flex_array_part *part) 353 { 354 int i; 355 356 for (i = 0; i < sizeof(struct flex_array_part); i++) 357 if (part->elements[i] != FLEX_ARRAY_FREE) 358 return 0; 359 return 1; 360 } 361 362 /** 363 * flex_array_shrink - free unused second-level pages 364 * @fa: the flex array to shrink 365 * 366 * Frees all second-level pages that consist solely of unused 367 * elements. Returns the number of pages freed. 368 * 369 * Locking must be provided by the caller. 370 */ 371 int flex_array_shrink(struct flex_array *fa) 372 { 373 struct flex_array_part *part; 374 int part_nr; 375 int ret = 0; 376 377 if (!fa->total_nr_elements || !fa->element_size) 378 return 0; 379 if (elements_fit_in_base(fa)) 380 return ret; 381 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) { 382 part = fa->parts[part_nr]; 383 if (!part) 384 continue; 385 if (part_is_free(part)) { 386 fa->parts[part_nr] = NULL; 387 kfree(part); 388 ret++; 389 } 390 } 391 return ret; 392 } 393 EXPORT_SYMBOL(flex_array_shrink);
Cache object: 2bdeb945375f304f635ffe95bac137bf
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