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
27struct flex_array_part {
28    char elements[FLEX_ARRAY_PART_SIZE];
29};
30
31/*
32 * If a user requests an allocation which is small
33 * enough, we may simply use the space in the
34 * flex_array->parts[] array to store the user
35 * data.
36 */
37static inline int elements_fit_in_base(struct flex_array *fa)
38{
39    int data_size = fa->element_size * fa->total_nr_elements;
40    if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
41        return 1;
42    return 0;
43}
44
45/**
46 * flex_array_alloc - allocate a new flexible array
47 * @element_size: the size of individual elements in the array
48 * @total: total number of elements that this should hold
49 * @flags: page allocation flags to use for base array
50 *
51 * Note: all locking must be provided by the caller.
52 *
53 * @total is used to size internal structures. If the user ever
54 * accesses any array indexes >=@total, it will produce errors.
55 *
56 * The maximum number of elements is defined as: the number of
57 * elements that can be stored in a page times the number of
58 * page pointers that we can fit in the base structure or (using
59 * integer math):
60 *
61 * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
62 *
63 * Here's a table showing example capacities. Note that the maximum
64 * index that the get/put() functions is just nr_objects-1. This
65 * basically means that you get 4MB of storage on 32-bit and 2MB on
66 * 64-bit.
67 *
68 *
69 * Element size | Objects | Objects |
70 * PAGE_SIZE=4k | 32-bit | 64-bit |
71 * ---------------------------------|
72 * 1 bytes | 4186112 | 2093056 |
73 * 2 bytes | 2093056 | 1046528 |
74 * 3 bytes | 1395030 | 697515 |
75 * 4 bytes | 1046528 | 523264 |
76 * 32 bytes | 130816 | 65408 |
77 * 33 bytes | 126728 | 63364 |
78 * 2048 bytes | 2044 | 1022 |
79 * 2049 bytes | 1022 | 511 |
80 * void * | 1046528 | 261632 |
81 *
82 * Since 64-bit pointers are twice the size, we lose half the
83 * capacity in the base structure. Also note that no effort is made
84 * to efficiently pack objects across page boundaries.
85 */
86struct flex_array *flex_array_alloc(int element_size, unsigned int total,
87                    gfp_t flags)
88{
89    struct flex_array *ret;
90    int max_size = FLEX_ARRAY_NR_BASE_PTRS *
91                FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
92
93    /* max_size will end up 0 if element_size > PAGE_SIZE */
94    if (total > max_size)
95        return NULL;
96    ret = kzalloc(sizeof(struct flex_array), flags);
97    if (!ret)
98        return NULL;
99    ret->element_size = element_size;
100    ret->total_nr_elements = total;
101    if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
102        memset(&ret->parts[0], FLEX_ARRAY_FREE,
103                        FLEX_ARRAY_BASE_BYTES_LEFT);
104    return ret;
105}
106
107static int fa_element_to_part_nr(struct flex_array *fa,
108                    unsigned int element_nr)
109{
110    return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
111}
112
113/**
114 * flex_array_free_parts - just free the second-level pages
115 * @fa: the flex array from which to free parts
116 *
117 * This is to be used in cases where the base 'struct flex_array'
118 * has been statically allocated and should not be free.
119 */
120void flex_array_free_parts(struct flex_array *fa)
121{
122    int part_nr;
123
124    if (elements_fit_in_base(fa))
125        return;
126    for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
127        kfree(fa->parts[part_nr]);
128}
129
130void flex_array_free(struct flex_array *fa)
131{
132    flex_array_free_parts(fa);
133    kfree(fa);
134}
135
136static unsigned int index_inside_part(struct flex_array *fa,
137                    unsigned int element_nr)
138{
139    unsigned int part_offset;
140
141    part_offset = element_nr %
142                FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
143    return part_offset * fa->element_size;
144}
145
146static struct flex_array_part *
147__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
148{
149    struct flex_array_part *part = fa->parts[part_nr];
150    if (!part) {
151        part = kmalloc(sizeof(struct flex_array_part), flags);
152        if (!part)
153            return NULL;
154        if (!(flags & __GFP_ZERO))
155            memset(part, FLEX_ARRAY_FREE,
156                sizeof(struct flex_array_part));
157        fa->parts[part_nr] = part;
158    }
159    return part;
160}
161
162/**
163 * flex_array_put - copy data into the array at @element_nr
164 * @fa: the flex array to copy data into
165 * @element_nr: index of the position in which to insert
166 * the new element.
167 * @src: address of data to copy into the array
168 * @flags: page allocation flags to use for array expansion
169 *
170 *
171 * Note that this *copies* the contents of @src into
172 * the array. If you are trying to store an array of
173 * pointers, make sure to pass in &ptr instead of ptr.
174 * You may instead wish to use the flex_array_put_ptr()
175 * helper function.
176 *
177 * Locking must be provided by the caller.
178 */
179int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
180            gfp_t flags)
181{
182    int part_nr = fa_element_to_part_nr(fa, element_nr);
183    struct flex_array_part *part;
184    void *dst;
185
186    if (element_nr >= fa->total_nr_elements)
187        return -ENOSPC;
188    if (elements_fit_in_base(fa))
189        part = (struct flex_array_part *)&fa->parts[0];
190    else {
191        part = __fa_get_part(fa, part_nr, flags);
192        if (!part)
193            return -ENOMEM;
194    }
195    dst = &part->elements[index_inside_part(fa, element_nr)];
196    memcpy(dst, src, fa->element_size);
197    return 0;
198}
199
200/**
201 * flex_array_clear - clear element in array at @element_nr
202 * @fa: the flex array of the element.
203 * @element_nr: index of the position to clear.
204 *
205 * Locking must be provided by the caller.
206 */
207int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
208{
209    int part_nr = fa_element_to_part_nr(fa, element_nr);
210    struct flex_array_part *part;
211    void *dst;
212
213    if (element_nr >= fa->total_nr_elements)
214        return -ENOSPC;
215    if (elements_fit_in_base(fa))
216        part = (struct flex_array_part *)&fa->parts[0];
217    else {
218        part = fa->parts[part_nr];
219        if (!part)
220            return -EINVAL;
221    }
222    dst = &part->elements[index_inside_part(fa, element_nr)];
223    memset(dst, FLEX_ARRAY_FREE, fa->element_size);
224    return 0;
225}
226
227/**
228 * flex_array_prealloc - guarantee that array space exists
229 * @fa: the flex array for which to preallocate parts
230 * @start: index of first array element for which space is allocated
231 * @end: index of last (inclusive) element for which space is allocated
232 * @flags: page allocation flags
233 *
234 * This will guarantee that no future calls to flex_array_put()
235 * will allocate memory. It can be used if you are expecting to
236 * be holding a lock or in some atomic context while writing
237 * data into the array.
238 *
239 * Locking must be provided by the caller.
240 */
241int flex_array_prealloc(struct flex_array *fa, unsigned int start,
242            unsigned int end, gfp_t flags)
243{
244    int start_part;
245    int end_part;
246    int part_nr;
247    struct flex_array_part *part;
248
249    if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
250        return -ENOSPC;
251    if (elements_fit_in_base(fa))
252        return 0;
253    start_part = fa_element_to_part_nr(fa, start);
254    end_part = fa_element_to_part_nr(fa, end);
255    for (part_nr = start_part; part_nr <= end_part; part_nr++) {
256        part = __fa_get_part(fa, part_nr, flags);
257        if (!part)
258            return -ENOMEM;
259    }
260    return 0;
261}
262
263/**
264 * flex_array_get - pull data back out of the array
265 * @fa: the flex array from which to extract data
266 * @element_nr: index of the element to fetch from the array
267 *
268 * Returns a pointer to the data at index @element_nr. Note
269 * that this is a copy of the data that was passed in. If you
270 * are using this to store pointers, you'll get back &ptr. You
271 * may instead wish to use the flex_array_get_ptr helper.
272 *
273 * Locking must be provided by the caller.
274 */
275void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
276{
277    int part_nr = fa_element_to_part_nr(fa, element_nr);
278    struct flex_array_part *part;
279
280    if (element_nr >= fa->total_nr_elements)
281        return NULL;
282    if (elements_fit_in_base(fa))
283        part = (struct flex_array_part *)&fa->parts[0];
284    else {
285        part = fa->parts[part_nr];
286        if (!part)
287            return NULL;
288    }
289    return &part->elements[index_inside_part(fa, element_nr)];
290}
291
292/**
293 * flex_array_get_ptr - pull a ptr back out of the array
294 * @fa: the flex array from which to extract data
295 * @element_nr: index of the element to fetch from the array
296 *
297 * Returns the pointer placed in the flex array at element_nr using
298 * flex_array_put_ptr(). This function should not be called if the
299 * element in question was not set using the _put_ptr() helper.
300 */
301void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
302{
303    void **tmp;
304
305    tmp = flex_array_get(fa, element_nr);
306    if (!tmp)
307        return NULL;
308
309    return *tmp;
310}
311
312static int part_is_free(struct flex_array_part *part)
313{
314    int i;
315
316    for (i = 0; i < sizeof(struct flex_array_part); i++)
317        if (part->elements[i] != FLEX_ARRAY_FREE)
318            return 0;
319    return 1;
320}
321
322/**
323 * flex_array_shrink - free unused second-level pages
324 * @fa: the flex array to shrink
325 *
326 * Frees all second-level pages that consist solely of unused
327 * elements. Returns the number of pages freed.
328 *
329 * Locking must be provided by the caller.
330 */
331int flex_array_shrink(struct flex_array *fa)
332{
333    struct flex_array_part *part;
334    int part_nr;
335    int ret = 0;
336
337    if (elements_fit_in_base(fa))
338        return ret;
339    for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
340        part = fa->parts[part_nr];
341        if (!part)
342            continue;
343        if (part_is_free(part)) {
344            fa->parts[part_nr] = NULL;
345            kfree(part);
346            ret++;
347        }
348    }
349    return ret;
350}
351

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