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);