linux/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
  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 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}
 117EXPORT_SYMBOL(flex_array_alloc);
 118
 119static 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 */
 132void 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}
 141EXPORT_SYMBOL(flex_array_free_parts);
 142
 143void flex_array_free(struct flex_array *fa)
 144{
 145        flex_array_free_parts(fa);
 146        kfree(fa);
 147}
 148EXPORT_SYMBOL(flex_array_free);
 149
 150static 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
 160static 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 */
 193int 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}
 216EXPORT_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 */
 225int 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}
 247EXPORT_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 */
 263int 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}
 296EXPORT_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 */
 310void *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}
 329EXPORT_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 */
 340void *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}
 350EXPORT_SYMBOL(flex_array_get_ptr);
 351
 352static 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 */
 371int 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}
 393EXPORT_SYMBOL(flex_array_shrink);
 394
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