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
27 struct flex_array_part {
28 char elements[FLEX_ARRAY_PART_SIZE];
29 };
30
31 static inline int __elements_per_part(int element_size)
32 {
33 return FLEX_ARRAY_PART_SIZE / element_size;
34 }
35
36 static inline int bytes_left_in_base(void)
37 {
38 int element_offset = offsetof(struct flex_array, parts);
39 int bytes_left = FLEX_ARRAY_BASE_SIZE - element_offset;
40 return bytes_left;
41 }
42
43 static inline int nr_base_part_ptrs(void)
44 {
45 return bytes_left_in_base() / sizeof(struct flex_array_part *);
46 }
47
48 /*
49 * If a user requests an allocation which is small
50 * enough, we may simply use the space in the
51 * flex_array->parts[] array to store the user
52 * data.
53 */
54 static inline int elements_fit_in_base(struct flex_array *fa)
55 {
56 int data_size = fa->element_size * fa->total_nr_elements;
57 if (data_size <= bytes_left_in_base())
58 return 1;
59 return 0;
60 }
61
62 /**
63 * flex_array_alloc - allocate a new flexible array
64 * @element_size: the size of individual elements in the array
65 * @total: total number of elements that this should hold
66 *
67 * Note: all locking must be provided by the caller.
68 *
69 * @total is used to size internal structures. If the user ever
70 * accesses any array indexes >=@total, it will produce errors.
71 *
72 * The maximum number of elements is defined as: the number of
73 * elements that can be stored in a page times the number of
74 * page pointers that we can fit in the base structure or (using
75 * integer math):
76 *
77 * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
78 *
79 * Here's a table showing example capacities. Note that the maximum
80 * index that the get/put() functions is just nr_objects-1. This
81 * basically means that you get 4MB of storage on 32-bit and 2MB on
82 * 64-bit.
83 *
84 *
85 * Element size | Objects | Objects |
86 * PAGE_SIZE=4k | 32-bit | 64-bit |
87 * ---------------------------------|
88 * 1 bytes | 4186112 | 2093056 |
89 * 2 bytes | 2093056 | 1046528 |
90 * 3 bytes | 1395030 | 697515 |
91 * 4 bytes | 1046528 | 523264 |
92 * 32 bytes | 130816 | 65408 |
93 * 33 bytes | 126728 | 63364 |
94 * 2048 bytes | 2044 | 1022 |
95 * 2049 bytes | 1022 | 511 |
96 * void * | 1046528 | 261632 |
97 *
98 * Since 64-bit pointers are twice the size, we lose half the
99 * capacity in the base structure. Also note that no effort is made
100 * to efficiently pack objects across page boundaries.
101 */
102 struct flex_array *flex_array_alloc(int element_size, unsigned int total,
103 gfp_t flags)
104 {
105 struct flex_array *ret;
106 int max_size = nr_base_part_ptrs() * __elements_per_part(element_size);
107
108 /* max_size will end up 0 if element_size > PAGE_SIZE */
109 if (total > max_size)
110 return NULL;
111 ret = kzalloc(sizeof(struct flex_array), flags);
112 if (!ret)
113 return NULL;
114 ret->element_size = element_size;
115 ret->total_nr_elements = total;
116 return ret;
117 }
118
119 static int fa_element_to_part_nr(struct flex_array *fa,
120 unsigned int element_nr)
121 {
122 return element_nr / __elements_per_part(fa->element_size);
123 }
124
125 /**
126 * flex_array_free_parts - just free the second-level pages
127 *
128 * This is to be used in cases where the base 'struct flex_array'
129 * has been statically allocated and should not be free.
130 */
131 void flex_array_free_parts(struct flex_array *fa)
132 {
133 int part_nr;
134 int max_part = nr_base_part_ptrs();
135
136 if (elements_fit_in_base(fa))
137 return;
138 for (part_nr = 0; part_nr < max_part; part_nr++)
139 kfree(fa->parts[part_nr]);
140 }
141
142 void flex_array_free(struct flex_array *fa)
143 {
144 flex_array_free_parts(fa);
145 kfree(fa);
146 }
147
148 static unsigned int index_inside_part(struct flex_array *fa,
149 unsigned int element_nr)
150 {
151 unsigned int part_offset;
152
153 part_offset = element_nr % __elements_per_part(fa->element_size);
154 return part_offset * fa->element_size;
155 }
156
157 static struct flex_array_part *
158 __fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
159 {
160 struct flex_array_part *part = fa->parts[part_nr];
161 if (!part) {
162 /*
163 * This leaves the part pages uninitialized
164 * and with potentially random data, just
165 * as if the user had kmalloc()'d the whole.
166 * __GFP_ZERO can be used to zero it.
167 */
168 part = kmalloc(FLEX_ARRAY_PART_SIZE, flags);
169 if (!part)
170 return NULL;
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 * @src: address of data to copy into the array
179 * @element_nr: index of the position in which to insert
180 * the new element.
181 *
182 * Note that this *copies* the contents of @src into
183 * the array. If you are trying to store an array of
184 * pointers, make sure to pass in &ptr instead of ptr.
185 *
186 * Locking must be provided by the caller.
187 */
188 int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
189 gfp_t flags)
190 {
191 int part_nr = fa_element_to_part_nr(fa, element_nr);
192 struct flex_array_part *part;
193 void *dst;
194
195 if (element_nr >= fa->total_nr_elements)
196 return -ENOSPC;
197 if (elements_fit_in_base(fa))
198 part = (struct flex_array_part *)&fa->parts[0];
199 else {
200 part = __fa_get_part(fa, part_nr, flags);
201 if (!part)
202 return -ENOMEM;
203 }
204 dst = &part->elements[index_inside_part(fa, element_nr)];
205 memcpy(dst, src, fa->element_size);
206 return 0;
207 }
208
209 /**
210 * flex_array_prealloc - guarantee that array space exists
211 * @start: index of first array element for which space is allocated
212 * @end: index of last (inclusive) element for which space is allocated
213 *
214 * This will guarantee that no future calls to flex_array_put()
215 * will allocate memory. It can be used if you are expecting to
216 * be holding a lock or in some atomic context while writing
217 * data into the array.
218 *
219 * Locking must be provided by the caller.
220 */
221 int flex_array_prealloc(struct flex_array *fa, unsigned int start,
222 unsigned int end, gfp_t flags)
223 {
224 int start_part;
225 int end_part;
226 int part_nr;
227 struct flex_array_part *part;
228
229 if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
230 return -ENOSPC;
231 if (elements_fit_in_base(fa))
232 return 0;
233 start_part = fa_element_to_part_nr(fa, start);
234 end_part = fa_element_to_part_nr(fa, end);
235 for (part_nr = start_part; part_nr <= end_part; part_nr++) {
236 part = __fa_get_part(fa, part_nr, flags);
237 if (!part)
238 return -ENOMEM;
239 }
240 return 0;
241 }
242
243 /**
244 * flex_array_get - pull data back out of the array
245 * @element_nr: index of the element to fetch from the array
246 *
247 * Returns a pointer to the data at index @element_nr. Note
248 * that this is a copy of the data that was passed in. If you
249 * are using this to store pointers, you'll get back &ptr.
250 *
251 * Locking must be provided by the caller.
252 */
253 void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
254 {
255 int part_nr = fa_element_to_part_nr(fa, element_nr);
256 struct flex_array_part *part;
257
258 if (element_nr >= fa->total_nr_elements)
259 return NULL;
260 if (elements_fit_in_base(fa))
261 part = (struct flex_array_part *)&fa->parts[0];
262 else {
263 part = fa->parts[part_nr];
264 if (!part)
265 return NULL;
266 }
267 return &part->elements[index_inside_part(fa, element_nr)];
268 }
269
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