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 = FLEX_ARRAY_NR_BASE_PTRS *
  92                                 FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
  93
  94         /* max_size will end up 0 if element_size > PAGE_SIZE */
  95         if (total > max_size)
  96                 return NULL;
  97         ret = kzalloc(sizeof(struct flex_array), flags);
  98         if (!ret)
  99                 return NULL;
 100         ret->element_size = element_size;
 101         ret->total_nr_elements = total;
 102         if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
 103                 memset(&ret->parts[0], FLEX_ARRAY_FREE,
 104                                                 FLEX_ARRAY_BASE_BYTES_LEFT);
 105         return ret;
 106 }
 107 EXPORT_SYMBOL(flex_array_alloc);
 108
 109 static int fa_element_to_part_nr(struct flex_array *fa,
 110                                         unsigned int element_nr)
 111 {
 112         return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
 113 }
 114
 115 /**
 116  * flex_array_free_parts - just free the second-level pages
 117  * @fa:         the flex array from which to free parts
 118  *
 119  * This is to be used in cases where the base 'struct flex_array'
 120  * has been statically allocated and should not be free.
 121  */
 122 void flex_array_free_parts(struct flex_array *fa)
 123 {
 124         int part_nr;
 125
 126         if (elements_fit_in_base(fa))
 127                 return;
 128         for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
 129                 kfree(fa->parts[part_nr]);
 130 }
 131 EXPORT_SYMBOL(flex_array_free_parts);
 132
 133 void flex_array_free(struct flex_array *fa)
 134 {
 135         flex_array_free_parts(fa);
 136         kfree(fa);
 137 }
 138 EXPORT_SYMBOL(flex_array_free);
 139
 140 static unsigned int index_inside_part(struct flex_array *fa,
 141                                         unsigned int element_nr)
 142 {
 143         unsigned int part_offset;
 144
 145         part_offset = element_nr %
 146                                 FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
 147         return part_offset * fa->element_size;
 148 }
 149
 150 static struct flex_array_part *
 151 __fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
 152 {
 153         struct flex_array_part *part = fa->parts[part_nr];
 154         if (!part) {
 155                 part = kmalloc(sizeof(struct flex_array_part), flags);
 156                 if (!part)
 157                         return NULL;
 158                 if (!(flags & __GFP_ZERO))
 159                         memset(part, FLEX_ARRAY_FREE,
 160                                 sizeof(struct flex_array_part));
 161                 fa->parts[part_nr] = part;
 162         }
 163         return part;
 164 }
 165
 166 /**
 167  * flex_array_put - copy data into the array at @element_nr
 168  * @fa:         the flex array to copy data into
 169  * @element_nr: index of the position in which to insert
 170  *              the new element.
 171  * @src:        address of data to copy into the array
 172  * @flags:      page allocation flags to use for array expansion
 173  *
 174  *
 175  * Note that this *copies* the contents of @src into
 176  * the array.  If you are trying to store an array of
 177  * pointers, make sure to pass in &ptr instead of ptr.
 178  * You may instead wish to use the flex_array_put_ptr()
 179  * helper function.
 180  *
 181  * Locking must be provided by the caller.
 182  */
 183 int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
 184                         gfp_t flags)
 185 {
 186         int part_nr = fa_element_to_part_nr(fa, element_nr);
 187         struct flex_array_part *part;
 188         void *dst;
 189
 190         if (element_nr >= fa->total_nr_elements)
 191                 return -ENOSPC;
 192         if (elements_fit_in_base(fa))
 193                 part = (struct flex_array_part *)&fa->parts[0];
 194         else {
 195                 part = __fa_get_part(fa, part_nr, flags);
 196                 if (!part)
 197                         return -ENOMEM;
 198         }
 199         dst = &part->elements[index_inside_part(fa, element_nr)];
 200         memcpy(dst, src, fa->element_size);
 201         return 0;
 202 }
 203 EXPORT_SYMBOL(flex_array_put);
 204
 205 /**
 206  * flex_array_clear - clear element in array at @element_nr
 207  * @fa:         the flex array of the element.
 208  * @element_nr: index of the position to clear.
 209  *
 210  * Locking must be provided by the caller.
 211  */
 212 int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
 213 {
 214         int part_nr = fa_element_to_part_nr(fa, element_nr);
 215         struct flex_array_part *part;
 216         void *dst;
 217
 218         if (element_nr >= fa->total_nr_elements)
 219                 return -ENOSPC;
 220         if (elements_fit_in_base(fa))
 221                 part = (struct flex_array_part *)&fa->parts[0];
 222         else {
 223                 part = fa->parts[part_nr];
 224                 if (!part)
 225                         return -EINVAL;
 226         }
 227         dst = &part->elements[index_inside_part(fa, element_nr)];
 228         memset(dst, FLEX_ARRAY_FREE, fa->element_size);
 229         return 0;
 230 }
 231 EXPORT_SYMBOL(flex_array_clear);
 232
 233 /**
 234  * flex_array_prealloc - guarantee that array space exists
 235  * @fa:                 the flex array for which to preallocate parts
 236  * @start:              index of first array element for which space is allocated
 237  * @nr_elements:        number of elements for which space is allocated
 238  * @flags:              page allocation flags
 239  *
 240  * This will guarantee that no future calls to flex_array_put()
 241  * will allocate memory.  It can be used if you are expecting to
 242  * be holding a lock or in some atomic context while writing
 243  * data into the array.
 244  *
 245  * Locking must be provided by the caller.
 246  */
 247 int flex_array_prealloc(struct flex_array *fa, unsigned int start,
 248                         unsigned int nr_elements, gfp_t flags)
 249 {
 250         int start_part;
 251         int end_part;
 252         int part_nr;
 253         unsigned int end;
 254         struct flex_array_part *part;
 255
 256         if (!start && !nr_elements)
 257                 return 0;
 258         if (start >= fa->total_nr_elements)
 259                 return -ENOSPC;
 260         if (!nr_elements)
 261                 return 0;
 262
 263         end = start + nr_elements - 1;
 264
 265         if (end >= fa->total_nr_elements)
 266                 return -ENOSPC;
 267         if (elements_fit_in_base(fa))
 268                 return 0;
 269         start_part = fa_element_to_part_nr(fa, start);
 270         end_part = fa_element_to_part_nr(fa, end);
 271         for (part_nr = start_part; part_nr <= end_part; part_nr++) {
 272                 part = __fa_get_part(fa, part_nr, flags);
 273                 if (!part)
 274                         return -ENOMEM;
 275         }
 276         return 0;
 277 }
 278 EXPORT_SYMBOL(flex_array_prealloc);
 279
 280 /**
 281  * flex_array_get - pull data back out of the array
 282  * @fa:         the flex array from which to extract data
 283  * @element_nr: index of the element to fetch from the array
 284  *
 285  * Returns a pointer to the data at index @element_nr.  Note
 286  * that this is a copy of the data that was passed in.  If you
 287  * are using this to store pointers, you'll get back &ptr.  You
 288  * may instead wish to use the flex_array_get_ptr helper.
 289  *
 290  * Locking must be provided by the caller.
 291  */
 292 void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
 293 {
 294         int part_nr = fa_element_to_part_nr(fa, element_nr);
 295         struct flex_array_part *part;
 296
 297         if (element_nr >= fa->total_nr_elements)
 298                 return NULL;
 299         if (elements_fit_in_base(fa))
 300                 part = (struct flex_array_part *)&fa->parts[0];
 301         else {
 302                 part = fa->parts[part_nr];
 303                 if (!part)
 304                         return NULL;
 305         }
 306         return &part->elements[index_inside_part(fa, element_nr)];
 307 }
 308 EXPORT_SYMBOL(flex_array_get);
 309
 310 /**
 311  * flex_array_get_ptr - pull a ptr back out of the array
 312  * @fa:         the flex array from which to extract data
 313  * @element_nr: index of the element to fetch from the array
 314  *
 315  * Returns the pointer placed in the flex array at element_nr using
 316  * flex_array_put_ptr().  This function should not be called if the
 317  * element in question was not set using the _put_ptr() helper.
 318  */
 319 void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
 320 {
 321         void **tmp;
 322
 323         tmp = flex_array_get(fa, element_nr);
 324         if (!tmp)
 325                 return NULL;
 326
 327         return *tmp;
 328 }
 329 EXPORT_SYMBOL(flex_array_get_ptr);
 330
 331 static int part_is_free(struct flex_array_part *part)
 332 {
 333         int i;
 334
 335         for (i = 0; i < sizeof(struct flex_array_part); i++)
 336                 if (part->elements[i] != FLEX_ARRAY_FREE)
 337                         return 0;
 338         return 1;
 339 }
 340
 341 /**
 342  * flex_array_shrink - free unused second-level pages
 343  * @fa:         the flex array to shrink
 344  *
 345  * Frees all second-level pages that consist solely of unused
 346  * elements.  Returns the number of pages freed.
 347  *
 348  * Locking must be provided by the caller.
 349  */
 350 int flex_array_shrink(struct flex_array *fa)
 351 {
 352         struct flex_array_part *part;
 353         int part_nr;
 354         int ret = 0;
 355
 356         if (!fa->total_nr_elements)
 357                 return 0;
 358         if (elements_fit_in_base(fa))
 359                 return ret;
 360         for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
 361                 part = fa->parts[part_nr];
 362                 if (!part)
 363                         continue;
 364                 if (part_is_free(part)) {
 365                         fa->parts[part_nr] = NULL;
 366                         kfree(part);
 367                         ret++;
 368                 }
 369         }
 370         return ret;
 371 }
 372 EXPORT_SYMBOL(flex_array_shrink);