LXR linux/lib/flex

   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