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/module.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);