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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); |
399 |
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