lib/flex_array.c

   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 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 }
 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         /*
 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  */
 137 void 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 }
 146 EXPORT_SYMBOL(flex_array_free_parts);
 147
 148 void flex_array_free(struct flex_array *fa)
 149 {
 150         flex_array_free_parts(fa);
 151         kfree(fa);
 152 }
 153 EXPORT_SYMBOL(flex_array_free);
 154
 155 static 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
 165 static 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  */
 198 int 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 }
 221 EXPORT_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  */
 230 int 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 }
 252 EXPORT_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  */
 268 int 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 }
 301 EXPORT_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  */
 315 void *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 }
 334 EXPORT_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  */
 345 void *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 }
 355 EXPORT_SYMBOL(flex_array_get_ptr);
 356
 357 static 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  */
 376 int 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 }
 398 EXPORT_SYMBOL(flex_array_shrink);