Root/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
29struct 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 */
39static 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 */
88struct 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}
117EXPORT_SYMBOL(flex_array_alloc);
118
119static 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 */
132void 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}
141EXPORT_SYMBOL(flex_array_free_parts);
142
143void flex_array_free(struct flex_array *fa)
144{
145    flex_array_free_parts(fa);
146    kfree(fa);
147}
148EXPORT_SYMBOL(flex_array_free);
149
150static 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
160static 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 */
193int 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}
216EXPORT_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 */
225int 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}
247EXPORT_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 */
263int 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}
296EXPORT_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 */
310void *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}
329EXPORT_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 */
340void *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}
350EXPORT_SYMBOL(flex_array_get_ptr);
351
352static 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 */
371int 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}
393EXPORT_SYMBOL(flex_array_shrink);
394

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