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
  28 struct flex_array_part {
  29         char elements[FLEX_ARRAY_PART_SIZE];
  30 };
  31
  32 /*
  33  * If a user requests an allocation which is small
  34  * enough, we may simply use the space in the
  35  * flex_array->parts[] array to store the user
  36  * data.
  37  */
  38 static inline int elements_fit_in_base(struct flex_array *fa)
  39 {
  40         int data_size = fa->element_size * fa->total_nr_elements;
  41         if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
  42                 return 1;
  43         return 0;
  44 }
  45
  46 /**
  47  * flex_array_alloc - allocate a new flexible array
  48  * @element_size:       the size of individual elements in the array
  49  * @total:              total number of elements that this should hold
  50  * @flags:              page allocation flags to use for base array
  51  *
  52  * Note: all locking must be provided by the caller.
  53  *
  54  * @total is used to size internal structures.  If the user ever
  55  * accesses any array indexes >=@total, it will produce errors.
  56  *
  57  * The maximum number of elements is defined as: the number of
  58  * elements that can be stored in a page times the number of
  59  * page pointers that we can fit in the base structure or (using
  60  * integer math):
  61  *
  62  *      (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
  63  *
  64  * Here's a table showing example capacities.  Note that the maximum
  65  * index that the get/put() functions is just nr_objects-1.   This
  66  * basically means that you get 4MB of storage on 32-bit and 2MB on
  67  * 64-bit.
  68  *
  69  *
  70  * Element size | Objects | Objects |
  71  * PAGE_SIZE=4k |  32-bit |  64-bit |
  72  * ---------------------------------|
  73  *      1 bytes | 4186112 | 2093056 |
  74  *      2 bytes | 2093056 | 1046528 |
  75  *      3 bytes | 1395030 |  697515 |
  76  *      4 bytes | 1046528 |  523264 |
  77  *     32 bytes |  130816 |   65408 |
  78  *     33 bytes |  126728 |   63364 |
  79  *   2048 bytes |    2044 |    1022 |
  80  *   2049 bytes |    1022 |     511 |
  81  *       void * | 1046528 |  261632 |
  82  *
  83  * Since 64-bit pointers are twice the size, we lose half the
  84  * capacity in the base structure.  Also note that no effort is made
  85  * to efficiently pack objects across page boundaries.
  86  */
  87 struct flex_array *flex_array_alloc(int element_size, unsigned int total,
  88                                         gfp_t flags)
  89 {
  90         struct flex_array *ret;
  91         int max_size = 0;
  92
  93         if (element_size)
  94                 max_size = FLEX_ARRAY_NR_BASE_PTRS *
  95                            FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
  96
  97         /* max_size will end up 0 if element_size > PAGE_SIZE */
  98         if (total > max_size)
  99                 return NULL;
 100         ret = kzalloc(sizeof(struct flex_array), flags);
 101         if (!ret)
 102                 return NULL;
 103         ret->element_size = element_size;
 104         ret->total_nr_elements = total;
 105         if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
 106                 memset(&ret->parts[0], FLEX_ARRAY_FREE,
 107                                                 FLEX_ARRAY_BASE_BYTES_LEFT);
 108         return ret;
 109 }
 110 EXPORT_SYMBOL(flex_array_alloc);
 111
 112 static int fa_element_to_part_nr(struct flex_array *fa,
 113                                         unsigned int element_nr)
 114 {
 115         return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
 116 }
 117
 118 /**
 119  * flex_array_free_parts - just free the second-level pages
 120  * @fa:         the flex array from which to free parts
 121  *
 122  * This is to be used in cases where the base 'struct flex_array'
 123  * has been statically allocated and should not be free.
 124  */
 125 void flex_array_free_parts(struct flex_array *fa)
 126 {
 127         int part_nr;
 128
 129         if (elements_fit_in_base(fa))
 130                 return;
 131         for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
 132                 kfree(fa->parts[part_nr]);
 133 }
 134 EXPORT_SYMBOL(flex_array_free_parts);
 135
 136 void flex_array_free(struct flex_array *fa)
 137 {
 138         flex_array_free_parts(fa);
 139         kfree(fa);
 140 }
 141 EXPORT_SYMBOL(flex_array_free);
 142
 143 static unsigned int index_inside_part(struct flex_array *fa,
 144                                         unsigned int element_nr)
 145 {
 146         unsigned int part_offset;
 147
 148         part_offset = element_nr %
 149                                 FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
 150         return part_offset * fa->element_size;
 151 }
 152
 153 static struct flex_array_part *
 154 __fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
 155 {
 156         struct flex_array_part *part = fa->parts[part_nr];
 157         if (!part) {
 158                 part = kmalloc(sizeof(struct flex_array_part), flags);
 159                 if (!part)
 160                         return NULL;
 161                 if (!(flags & __GFP_ZERO))
 162                         memset(part, FLEX_ARRAY_FREE,
 163                                 sizeof(struct flex_array_part));
 164                 fa->parts[part_nr] = part;
 165         }
 166         return part;
 167 }
 168
 169 /**
 170  * flex_array_put - copy data into the array at @element_nr
 171  * @fa:         the flex array to copy data into
 172  * @element_nr: index of the position in which to insert
 173  *              the new element.
 174  * @src:        address of data to copy into the array
 175  * @flags:      page allocation flags to use for array expansion
 176  *
 177  *
 178  * Note that this *copies* the contents of @src into
 179  * the array.  If you are trying to store an array of
 180  * pointers, make sure to pass in &ptr instead of ptr.
 181  * You may instead wish to use the flex_array_put_ptr()
 182  * helper function.
 183  *
 184  * Locking must be provided by the caller.
 185  */
 186 int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
 187                         gfp_t flags)
 188 {
 189         int part_nr;
 190         struct flex_array_part *part;
 191         void *dst;
 192
 193         if (element_nr >= fa->total_nr_elements)
 194                 return -ENOSPC;
 195         if (!fa->element_size)
 196                 return 0;
 197         if (elements_fit_in_base(fa))
 198                 part = (struct flex_array_part *)&fa->parts[0];
 199         else {
 200                 part_nr = fa_element_to_part_nr(fa, element_nr);
 201                 part = __fa_get_part(fa, part_nr, flags);
 202                 if (!part)
 203                         return -ENOMEM;
 204         }
 205         dst = &part->elements[index_inside_part(fa, element_nr)];
 206         memcpy(dst, src, fa->element_size);
 207         return 0;
 208 }
 209 EXPORT_SYMBOL(flex_array_put);
 210
 211 /**
 212  * flex_array_clear - clear element in array at @element_nr
 213  * @fa:         the flex array of the element.
 214  * @element_nr: index of the position to clear.
 215  *
 216  * Locking must be provided by the caller.
 217  */
 218 int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
 219 {
 220         int part_nr;
 221         struct flex_array_part *part;
 222         void *dst;
 223
 224         if (element_nr >= fa->total_nr_elements)
 225                 return -ENOSPC;
 226         if (!fa->element_size)
 227                 return 0;
 228         if (elements_fit_in_base(fa))
 229                 part = (struct flex_array_part *)&fa->parts[0];
 230         else {
 231                 part_nr = fa_element_to_part_nr(fa, element_nr);
 232                 part = fa->parts[part_nr];
 233                 if (!part)
 234                         return -EINVAL;
 235         }
 236         dst = &part->elements[index_inside_part(fa, element_nr)];
 237         memset(dst, FLEX_ARRAY_FREE, fa->element_size);
 238         return 0;
 239 }
 240 EXPORT_SYMBOL(flex_array_clear);
 241
 242 /**
 243  * flex_array_prealloc - guarantee that array space exists
 244  * @fa:                 the flex array for which to preallocate parts
 245  * @start:              index of first array element for which space is allocated
 246  * @nr_elements:        number of elements for which space is allocated
 247  * @flags:              page allocation flags
 248  *
 249  * This will guarantee that no future calls to flex_array_put()
 250  * will allocate memory.  It can be used if you are expecting to
 251  * be holding a lock or in some atomic context while writing
 252  * data into the array.
 253  *
 254  * Locking must be provided by the caller.
 255  */
 256 int flex_array_prealloc(struct flex_array *fa, unsigned int start,
 257                         unsigned int nr_elements, gfp_t flags)
 258 {
 259         int start_part;
 260         int end_part;
 261         int part_nr;
 262         unsigned int end;
 263         struct flex_array_part *part;
 264
 265         if (!start && !nr_elements)
 266                 return 0;
 267         if (start >= fa->total_nr_elements)
 268                 return -ENOSPC;
 269         if (!nr_elements)
 270                 return 0;
 271
 272         end = start + nr_elements - 1;
 273
 274         if (end >= fa->total_nr_elements)
 275                 return -ENOSPC;
 276         if (!fa->element_size)
 277                 return 0;
 278         if (elements_fit_in_base(fa))
 279                 return 0;
 280         start_part = fa_element_to_part_nr(fa, start);
 281         end_part = fa_element_to_part_nr(fa, end);
 282         for (part_nr = start_part; part_nr <= end_part; part_nr++) {
 283                 part = __fa_get_part(fa, part_nr, flags);
 284                 if (!part)
 285                         return -ENOMEM;
 286         }
 287         return 0;
 288 }
 289 EXPORT_SYMBOL(flex_array_prealloc);
 290
 291 /**
 292  * flex_array_get - pull data back out of the array
 293  * @fa:         the flex array from which to extract data
 294  * @element_nr: index of the element to fetch from the array
 295  *
 296  * Returns a pointer to the data at index @element_nr.  Note
 297  * that this is a copy of the data that was passed in.  If you
 298  * are using this to store pointers, you'll get back &ptr.  You
 299  * may instead wish to use the flex_array_get_ptr helper.
 300  *
 301  * Locking must be provided by the caller.
 302  */
 303 void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
 304 {
 305         int part_nr;
 306         struct flex_array_part *part;
 307
 308         if (!fa->element_size)
 309                 return NULL;
 310         if (element_nr >= fa->total_nr_elements)
 311                 return NULL;
 312         if (elements_fit_in_base(fa))
 313                 part = (struct flex_array_part *)&fa->parts[0];
 314         else {
 315                 part_nr = fa_element_to_part_nr(fa, element_nr);
 316                 part = fa->parts[part_nr];
 317                 if (!part)
 318                         return NULL;
 319         }
 320         return &part->elements[index_inside_part(fa, element_nr)];
 321 }
 322 EXPORT_SYMBOL(flex_array_get);
 323
 324 /**
 325  * flex_array_get_ptr - pull a ptr back out of the array
 326  * @fa:         the flex array from which to extract data
 327  * @element_nr: index of the element to fetch from the array
 328  *
 329  * Returns the pointer placed in the flex array at element_nr using
 330  * flex_array_put_ptr().  This function should not be called if the
 331  * element in question was not set using the _put_ptr() helper.
 332  */
 333 void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
 334 {
 335         void **tmp;
 336
 337         tmp = flex_array_get(fa, element_nr);
 338         if (!tmp)
 339                 return NULL;
 340
 341         return *tmp;
 342 }
 343 EXPORT_SYMBOL(flex_array_get_ptr);
 344
 345 static int part_is_free(struct flex_array_part *part)
 346 {
 347         int i;
 348
 349         for (i = 0; i < sizeof(struct flex_array_part); i++)
 350                 if (part->elements[i] != FLEX_ARRAY_FREE)
 351                         return 0;
 352         return 1;
 353 }
 354
 355 /**
 356  * flex_array_shrink - free unused second-level pages
 357  * @fa:         the flex array to shrink
 358  *
 359  * Frees all second-level pages that consist solely of unused
 360  * elements.  Returns the number of pages freed.
 361  *
 362  * Locking must be provided by the caller.
 363  */
 364 int flex_array_shrink(struct flex_array *fa)
 365 {
 366         struct flex_array_part *part;
 367         int part_nr;
 368         int ret = 0;
 369
 370         if (!fa->total_nr_elements || !fa->element_size)
 371                 return 0;
 372         if (elements_fit_in_base(fa))
 373                 return ret;
 374         for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
 375                 part = fa->parts[part_nr];
 376                 if (!part)
 377                         continue;
 378                 if (part_is_free(part)) {
 379                         fa->parts[part_nr] = NULL;
 380                         kfree(part);
 381                         ret++;
 382                 }
 383         }
 384         return ret;
 385 }
 386 EXPORT_SYMBOL(flex_array_shrink);