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 29struct 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 */ 39static 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 */ 88struct 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 max_size = 0; 94 struct reciprocal_value reciprocal_elems = { 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} 117EXPORT_SYMBOL(flex_array_alloc); 118 119static int fa_element_to_part_nr(struct flex_array *fa, 120 unsigned int element_nr) 121{ 122 /* 123 * if element_size == 0 we don't get here, so we never touch 124 * the zeroed fa->reciprocal_elems, which would yield invalid 125 * results 126 */ 127 return reciprocal_divide(element_nr, fa->reciprocal_elems); 128} 129 130/** 131 * flex_array_free_parts - just free the second-level pages 132 * @fa: the flex array from which to free parts 133 * 134 * This is to be used in cases where the base 'struct flex_array' 135 * has been statically allocated and should not be free. 136 */ 137void flex_array_free_parts(struct flex_array *fa) 138{ 139 int part_nr; 140 141 if (elements_fit_in_base(fa)) 142 return; 143 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) 144 kfree(fa->parts[part_nr]); 145} 146EXPORT_SYMBOL(flex_array_free_parts); 147 148void flex_array_free(struct flex_array *fa) 149{ 150 flex_array_free_parts(fa); 151 kfree(fa); 152} 153EXPORT_SYMBOL(flex_array_free); 154 155static unsigned int index_inside_part(struct flex_array *fa, 156 unsigned int element_nr, 157 unsigned int part_nr) 158{ 159 unsigned int part_offset; 160 161 part_offset = element_nr - part_nr * fa->elems_per_part; 162 return part_offset * fa->element_size; 163} 164 165static struct flex_array_part * 166__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags) 167{ 168 struct flex_array_part *part = fa->parts[part_nr]; 169 if (!part) { 170 part = kmalloc(sizeof(struct flex_array_part), flags); 171 if (!part) 172 return NULL; 173 if (!(flags & __GFP_ZERO)) 174 memset(part, FLEX_ARRAY_FREE, 175 sizeof(struct flex_array_part)); 176 fa->parts[part_nr] = part; 177 } 178 return part; 179} 180 181/** 182 * flex_array_put - copy data into the array at @element_nr 183 * @fa: the flex array to copy data into 184 * @element_nr: index of the position in which to insert 185 * the new element. 186 * @src: address of data to copy into the array 187 * @flags: page allocation flags to use for array expansion 188 * 189 * 190 * Note that this *copies* the contents of @src into 191 * the array. If you are trying to store an array of 192 * pointers, make sure to pass in &ptr instead of ptr. 193 * You may instead wish to use the flex_array_put_ptr() 194 * helper function. 195 * 196 * Locking must be provided by the caller. 197 */ 198int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src, 199 gfp_t flags) 200{ 201 int part_nr = 0; 202 struct flex_array_part *part; 203 void *dst; 204 205 if (element_nr >= fa->total_nr_elements) 206 return -ENOSPC; 207 if (!fa->element_size) 208 return 0; 209 if (elements_fit_in_base(fa)) 210 part = (struct flex_array_part *)&fa->parts[0]; 211 else { 212 part_nr = fa_element_to_part_nr(fa, element_nr); 213 part = __fa_get_part(fa, part_nr, flags); 214 if (!part) 215 return -ENOMEM; 216 } 217 dst = &part->elements[index_inside_part(fa, element_nr, part_nr)]; 218 memcpy(dst, src, fa->element_size); 219 return 0; 220} 221EXPORT_SYMBOL(flex_array_put); 222 223/** 224 * flex_array_clear - clear element in array at @element_nr 225 * @fa: the flex array of the element. 226 * @element_nr: index of the position to clear. 227 * 228 * Locking must be provided by the caller. 229 */ 230int flex_array_clear(struct flex_array *fa, unsigned int element_nr) 231{ 232 int part_nr = 0; 233 struct flex_array_part *part; 234 void *dst; 235 236 if (element_nr >= fa->total_nr_elements) 237 return -ENOSPC; 238 if (!fa->element_size) 239 return 0; 240 if (elements_fit_in_base(fa)) 241 part = (struct flex_array_part *)&fa->parts[0]; 242 else { 243 part_nr = fa_element_to_part_nr(fa, element_nr); 244 part = fa->parts[part_nr]; 245 if (!part) 246 return -EINVAL; 247 } 248 dst = &part->elements[index_inside_part(fa, element_nr, part_nr)]; 249 memset(dst, FLEX_ARRAY_FREE, fa->element_size); 250 return 0; 251} 252EXPORT_SYMBOL(flex_array_clear); 253 254/** 255 * flex_array_prealloc - guarantee that array space exists 256 * @fa: the flex array for which to preallocate parts 257 * @start: index of first array element for which space is allocated 258 * @nr_elements: number of elements for which space is allocated 259 * @flags: page allocation flags 260 * 261 * This will guarantee that no future calls to flex_array_put() 262 * will allocate memory. It can be used if you are expecting to 263 * be holding a lock or in some atomic context while writing 264 * data into the array. 265 * 266 * Locking must be provided by the caller. 267 */ 268int flex_array_prealloc(struct flex_array *fa, unsigned int start, 269 unsigned int nr_elements, gfp_t flags) 270{ 271 int start_part; 272 int end_part; 273 int part_nr; 274 unsigned int end; 275 struct flex_array_part *part; 276 277 if (!start && !nr_elements) 278 return 0; 279 if (start >= fa->total_nr_elements) 280 return -ENOSPC; 281 if (!nr_elements) 282 return 0; 283 284 end = start + nr_elements - 1; 285 286 if (end >= fa->total_nr_elements) 287 return -ENOSPC; 288 if (!fa->element_size) 289 return 0; 290 if (elements_fit_in_base(fa)) 291 return 0; 292 start_part = fa_element_to_part_nr(fa, start); 293 end_part = fa_element_to_part_nr(fa, end); 294 for (part_nr = start_part; part_nr <= end_part; part_nr++) { 295 part = __fa_get_part(fa, part_nr, flags); 296 if (!part) 297 return -ENOMEM; 298 } 299 return 0; 300} 301EXPORT_SYMBOL(flex_array_prealloc); 302 303/** 304 * flex_array_get - pull data back out of the array 305 * @fa: the flex array from which to extract data 306 * @element_nr: index of the element to fetch from the array 307 * 308 * Returns a pointer to the data at index @element_nr. Note 309 * that this is a copy of the data that was passed in. If you 310 * are using this to store pointers, you'll get back &ptr. You 311 * may instead wish to use the flex_array_get_ptr helper. 312 * 313 * Locking must be provided by the caller. 314 */ 315void *flex_array_get(struct flex_array *fa, unsigned int element_nr) 316{ 317 int part_nr = 0; 318 struct flex_array_part *part; 319 320 if (!fa->element_size) 321 return NULL; 322 if (element_nr >= fa->total_nr_elements) 323 return NULL; 324 if (elements_fit_in_base(fa)) 325 part = (struct flex_array_part *)&fa->parts[0]; 326 else { 327 part_nr = fa_element_to_part_nr(fa, element_nr); 328 part = fa->parts[part_nr]; 329 if (!part) 330 return NULL; 331 } 332 return &part->elements[index_inside_part(fa, element_nr, part_nr)]; 333} 334EXPORT_SYMBOL(flex_array_get); 335 336/** 337 * flex_array_get_ptr - pull a ptr back out of the array 338 * @fa: the flex array from which to extract data 339 * @element_nr: index of the element to fetch from the array 340 * 341 * Returns the pointer placed in the flex array at element_nr using 342 * flex_array_put_ptr(). This function should not be called if the 343 * element in question was not set using the _put_ptr() helper. 344 */ 345void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr) 346{ 347 void **tmp; 348 349 tmp = flex_array_get(fa, element_nr); 350 if (!tmp) 351 return NULL; 352 353 return *tmp; 354} 355EXPORT_SYMBOL(flex_array_get_ptr); 356 357static int part_is_free(struct flex_array_part *part) 358{ 359 int i; 360 361 for (i = 0; i < sizeof(struct flex_array_part); i++) 362 if (part->elements[i] != FLEX_ARRAY_FREE) 363 return 0; 364 return 1; 365} 366 367/** 368 * flex_array_shrink - free unused second-level pages 369 * @fa: the flex array to shrink 370 * 371 * Frees all second-level pages that consist solely of unused 372 * elements. Returns the number of pages freed. 373 * 374 * Locking must be provided by the caller. 375 */ 376int flex_array_shrink(struct flex_array *fa) 377{ 378 struct flex_array_part *part; 379 int part_nr; 380 int ret = 0; 381 382 if (!fa->total_nr_elements || !fa->element_size) 383 return 0; 384 if (elements_fit_in_base(fa)) 385 return ret; 386 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) { 387 part = fa->parts[part_nr]; 388 if (!part) 389 continue; 390 if (part_is_free(part)) { 391 fa->parts[part_nr] = NULL; 392 kfree(part); 393 ret++; 394 } 395 } 396 return ret; 397} 398EXPORT_SYMBOL(flex_array_shrink); 399