1 /*
2 * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
3 *
4 * Scatterlist handling helpers.
5 *
6 * This source code is licensed under the GNU General Public License,
7 * Version 2. See the file COPYING for more details.
8 */
9 #include <linux/module.h>
10 #include <linux/scatterlist.h>
11 #include <linux/highmem.h>
12
13 /**
14 * sg_next - return the next scatterlist entry in a list
15 * @sg: The current sg entry
16 *
17 * Description:
18 * Usually the next entry will be @sg@ + 1, but if this sg element is part
19 * of a chained scatterlist, it could jump to the start of a new
20 * scatterlist array.
21 *
22 **/
sg_next(struct scatterlist * sg)23 struct scatterlist *sg_next(struct scatterlist *sg)
24 {
25 #ifdef CONFIG_DEBUG_SG
26 BUG_ON(sg->sg_magic != SG_MAGIC);
27 #endif
28 if (sg_is_last(sg))
29 return NULL;
30
31 sg++;
32 if (unlikely(sg_is_chain(sg)))
33 sg = sg_chain_ptr(sg);
34
35 return sg;
36 }
37 EXPORT_SYMBOL(sg_next);
38
39 /**
40 * sg_last - return the last scatterlist entry in a list
41 * @sgl: First entry in the scatterlist
42 * @nents: Number of entries in the scatterlist
43 *
44 * Description:
45 * Should only be used casually, it (currently) scans the entire list
46 * to get the last entry.
47 *
48 * Note that the @sgl@ pointer passed in need not be the first one,
49 * the important bit is that @nents@ denotes the number of entries that
50 * exist from @sgl@.
51 *
52 **/
sg_last(struct scatterlist * sgl,unsigned int nents)53 struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
54 {
55 #ifndef ARCH_HAS_SG_CHAIN
56 struct scatterlist *ret = &sgl[nents - 1];
57 #else
58 struct scatterlist *sg, *ret = NULL;
59 unsigned int i;
60
61 for_each_sg(sgl, sg, nents, i)
62 ret = sg;
63
64 #endif
65 #ifdef CONFIG_DEBUG_SG
66 BUG_ON(sgl[0].sg_magic != SG_MAGIC);
67 BUG_ON(!sg_is_last(ret));
68 #endif
69 return ret;
70 }
71 EXPORT_SYMBOL(sg_last);
72
73 /**
74 * sg_init_table - Initialize SG table
75 * @sgl: The SG table
76 * @nents: Number of entries in table
77 *
78 * Notes:
79 * If this is part of a chained sg table, sg_mark_end() should be
80 * used only on the last table part.
81 *
82 **/
sg_init_table(struct scatterlist * sgl,unsigned int nents)83 void sg_init_table(struct scatterlist *sgl, unsigned int nents)
84 {
85 memset(sgl, 0, sizeof(*sgl) * nents);
86 #ifdef CONFIG_DEBUG_SG
87 {
88 unsigned int i;
89 for (i = 0; i < nents; i++)
90 sgl[i].sg_magic = SG_MAGIC;
91 }
92 #endif
93 sg_mark_end(&sgl[nents - 1]);
94 }
95 EXPORT_SYMBOL(sg_init_table);
96
97 /**
98 * sg_init_one - Initialize a single entry sg list
99 * @sg: SG entry
100 * @buf: Virtual address for IO
101 * @buflen: IO length
102 *
103 **/
sg_init_one(struct scatterlist * sg,const void * buf,unsigned int buflen)104 void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
105 {
106 sg_init_table(sg, 1);
107 sg_set_buf(sg, buf, buflen);
108 }
109 EXPORT_SYMBOL(sg_init_one);
110
111 /*
112 * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
113 * helpers.
114 */
sg_kmalloc(unsigned int nents,gfp_t gfp_mask)115 static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
116 {
117 if (nents == SG_MAX_SINGLE_ALLOC)
118 return (struct scatterlist *) __get_free_page(gfp_mask);
119 else
120 return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
121 }
122
sg_kfree(struct scatterlist * sg,unsigned int nents)123 static void sg_kfree(struct scatterlist *sg, unsigned int nents)
124 {
125 if (nents == SG_MAX_SINGLE_ALLOC)
126 free_page((unsigned long) sg);
127 else
128 kfree(sg);
129 }
130
131 /**
132 * __sg_free_table - Free a previously mapped sg table
133 * @table: The sg table header to use
134 * @max_ents: The maximum number of entries per single scatterlist
135 * @free_fn: Free function
136 *
137 * Description:
138 * Free an sg table previously allocated and setup with
139 * __sg_alloc_table(). The @max_ents value must be identical to
140 * that previously used with __sg_alloc_table().
141 *
142 **/
__sg_free_table(struct sg_table * table,unsigned int max_ents,sg_free_fn * free_fn)143 void __sg_free_table(struct sg_table *table, unsigned int max_ents,
144 sg_free_fn *free_fn)
145 {
146 struct scatterlist *sgl, *next;
147
148 if (unlikely(!table->sgl))
149 return;
150
151 sgl = table->sgl;
152 while (table->orig_nents) {
153 unsigned int alloc_size = table->orig_nents;
154 unsigned int sg_size;
155
156 /*
157 * If we have more than max_ents segments left,
158 * then assign 'next' to the sg table after the current one.
159 * sg_size is then one less than alloc size, since the last
160 * element is the chain pointer.
161 */
162 if (alloc_size > max_ents) {
163 next = sg_chain_ptr(&sgl[max_ents - 1]);
164 alloc_size = max_ents;
165 sg_size = alloc_size - 1;
166 } else {
167 sg_size = alloc_size;
168 next = NULL;
169 }
170
171 table->orig_nents -= sg_size;
172 free_fn(sgl, alloc_size);
173 sgl = next;
174 }
175
176 table->sgl = NULL;
177 }
178 EXPORT_SYMBOL(__sg_free_table);
179
180 /**
181 * sg_free_table - Free a previously allocated sg table
182 * @table: The mapped sg table header
183 *
184 **/
sg_free_table(struct sg_table * table)185 void sg_free_table(struct sg_table *table)
186 {
187 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
188 }
189 EXPORT_SYMBOL(sg_free_table);
190
191 /**
192 * __sg_alloc_table - Allocate and initialize an sg table with given allocator
193 * @table: The sg table header to use
194 * @nents: Number of entries in sg list
195 * @max_ents: The maximum number of entries the allocator returns per call
196 * @gfp_mask: GFP allocation mask
197 * @alloc_fn: Allocator to use
198 *
199 * Description:
200 * This function returns a @table @nents long. The allocator is
201 * defined to return scatterlist chunks of maximum size @max_ents.
202 * Thus if @nents is bigger than @max_ents, the scatterlists will be
203 * chained in units of @max_ents.
204 *
205 * Notes:
206 * If this function returns non-0 (eg failure), the caller must call
207 * __sg_free_table() to cleanup any leftover allocations.
208 *
209 **/
__sg_alloc_table(struct sg_table * table,unsigned int nents,unsigned int max_ents,gfp_t gfp_mask,sg_alloc_fn * alloc_fn)210 int __sg_alloc_table(struct sg_table *table, unsigned int nents,
211 unsigned int max_ents, gfp_t gfp_mask,
212 sg_alloc_fn *alloc_fn)
213 {
214 struct scatterlist *sg, *prv;
215 unsigned int left;
216
217 #ifndef ARCH_HAS_SG_CHAIN
218 BUG_ON(nents > max_ents);
219 #endif
220
221 memset(table, 0, sizeof(*table));
222
223 left = nents;
224 prv = NULL;
225 do {
226 unsigned int sg_size, alloc_size = left;
227
228 if (alloc_size > max_ents) {
229 alloc_size = max_ents;
230 sg_size = alloc_size - 1;
231 } else
232 sg_size = alloc_size;
233
234 left -= sg_size;
235
236 sg = alloc_fn(alloc_size, gfp_mask);
237 if (unlikely(!sg))
238 return -ENOMEM;
239
240 sg_init_table(sg, alloc_size);
241 table->nents = table->orig_nents += sg_size;
242
243 /*
244 * If this is the first mapping, assign the sg table header.
245 * If this is not the first mapping, chain previous part.
246 */
247 if (prv)
248 sg_chain(prv, max_ents, sg);
249 else
250 table->sgl = sg;
251
252 /*
253 * If no more entries after this one, mark the end
254 */
255 if (!left)
256 sg_mark_end(&sg[sg_size - 1]);
257
258 /*
259 * only really needed for mempool backed sg allocations (like
260 * SCSI), a possible improvement here would be to pass the
261 * table pointer into the allocator and let that clear these
262 * flags
263 */
264 gfp_mask &= ~__GFP_WAIT;
265 gfp_mask |= __GFP_HIGH;
266 prv = sg;
267 } while (left);
268
269 return 0;
270 }
271 EXPORT_SYMBOL(__sg_alloc_table);
272
273 /**
274 * sg_alloc_table - Allocate and initialize an sg table
275 * @table: The sg table header to use
276 * @nents: Number of entries in sg list
277 * @gfp_mask: GFP allocation mask
278 *
279 * Description:
280 * Allocate and initialize an sg table. If @nents@ is larger than
281 * SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
282 *
283 **/
sg_alloc_table(struct sg_table * table,unsigned int nents,gfp_t gfp_mask)284 int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
285 {
286 int ret;
287
288 ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
289 gfp_mask, sg_kmalloc);
290 if (unlikely(ret))
291 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
292
293 return ret;
294 }
295 EXPORT_SYMBOL(sg_alloc_table);
296
297 /**
298 * sg_miter_start - start mapping iteration over a sg list
299 * @miter: sg mapping iter to be started
300 * @sgl: sg list to iterate over
301 * @nents: number of sg entries
302 *
303 * Description:
304 * Starts mapping iterator @miter.
305 *
306 * Context:
307 * Don't care.
308 */
sg_miter_start(struct sg_mapping_iter * miter,struct scatterlist * sgl,unsigned int nents,unsigned int flags)309 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
310 unsigned int nents, unsigned int flags)
311 {
312 memset(miter, 0, sizeof(struct sg_mapping_iter));
313
314 miter->__sg = sgl;
315 miter->__nents = nents;
316 miter->__offset = 0;
317 miter->__flags = flags;
318 }
319 EXPORT_SYMBOL(sg_miter_start);
320
321 /**
322 * sg_miter_next - proceed mapping iterator to the next mapping
323 * @miter: sg mapping iter to proceed
324 *
325 * Description:
326 * Proceeds @miter@ to the next mapping. @miter@ should have been
327 * started using sg_miter_start(). On successful return,
328 * @miter@->page, @miter@->addr and @miter@->length point to the
329 * current mapping.
330 *
331 * Context:
332 * IRQ disabled if SG_MITER_ATOMIC. IRQ must stay disabled till
333 * @miter@ is stopped. May sleep if !SG_MITER_ATOMIC.
334 *
335 * Returns:
336 * true if @miter contains the next mapping. false if end of sg
337 * list is reached.
338 */
sg_miter_next(struct sg_mapping_iter * miter)339 bool sg_miter_next(struct sg_mapping_iter *miter)
340 {
341 unsigned int off, len;
342
343 /* check for end and drop resources from the last iteration */
344 if (!miter->__nents)
345 return false;
346
347 sg_miter_stop(miter);
348
349 /* get to the next sg if necessary. __offset is adjusted by stop */
350 if (miter->__offset == miter->__sg->length && --miter->__nents) {
351 miter->__sg = sg_next(miter->__sg);
352 miter->__offset = 0;
353 }
354
355 /* map the next page */
356 off = miter->__sg->offset + miter->__offset;
357 len = miter->__sg->length - miter->__offset;
358
359 miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
360 off &= ~PAGE_MASK;
361 miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
362 miter->consumed = miter->length;
363
364 if (miter->__flags & SG_MITER_ATOMIC)
365 miter->addr = kmap_atomic(miter->page, KM_BIO_SRC_IRQ) + off;
366 else
367 miter->addr = kmap(miter->page) + off;
368
369 return true;
370 }
371 EXPORT_SYMBOL(sg_miter_next);
372
373 /**
374 * sg_miter_stop - stop mapping iteration
375 * @miter: sg mapping iter to be stopped
376 *
377 * Description:
378 * Stops mapping iterator @miter. @miter should have been started
379 * started using sg_miter_start(). A stopped iteration can be
380 * resumed by calling sg_miter_next() on it. This is useful when
381 * resources (kmap) need to be released during iteration.
382 *
383 * Context:
384 * IRQ disabled if the SG_MITER_ATOMIC is set. Don't care otherwise.
385 */
sg_miter_stop(struct sg_mapping_iter * miter)386 void sg_miter_stop(struct sg_mapping_iter *miter)
387 {
388 WARN_ON(miter->consumed > miter->length);
389
390 /* drop resources from the last iteration */
391 if (miter->addr) {
392 miter->__offset += miter->consumed;
393
394 if (miter->__flags & SG_MITER_ATOMIC) {
395 WARN_ON(!irqs_disabled());
396 kunmap_atomic(miter->addr, KM_BIO_SRC_IRQ);
397 } else
398 kunmap(miter->page);
399
400 miter->page = NULL;
401 miter->addr = NULL;
402 miter->length = 0;
403 miter->consumed = 0;
404 }
405 }
406 EXPORT_SYMBOL(sg_miter_stop);
407
408 /**
409 * sg_copy_buffer - Copy data between a linear buffer and an SG list
410 * @sgl: The SG list
411 * @nents: Number of SG entries
412 * @buf: Where to copy from
413 * @buflen: The number of bytes to copy
414 * @to_buffer: transfer direction (non zero == from an sg list to a
415 * buffer, 0 == from a buffer to an sg list
416 *
417 * Returns the number of copied bytes.
418 *
419 **/
sg_copy_buffer(struct scatterlist * sgl,unsigned int nents,void * buf,size_t buflen,int to_buffer)420 static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
421 void *buf, size_t buflen, int to_buffer)
422 {
423 unsigned int offset = 0;
424 struct sg_mapping_iter miter;
425 unsigned long flags;
426
427 sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC);
428
429 local_irq_save(flags);
430
431 while (sg_miter_next(&miter) && offset < buflen) {
432 unsigned int len;
433
434 len = min(miter.length, buflen - offset);
435
436 if (to_buffer)
437 memcpy(buf + offset, miter.addr, len);
438 else {
439 memcpy(miter.addr, buf + offset, len);
440 flush_kernel_dcache_page(miter.page);
441 }
442
443 offset += len;
444 }
445
446 sg_miter_stop(&miter);
447
448 local_irq_restore(flags);
449 return offset;
450 }
451
452 /**
453 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
454 * @sgl: The SG list
455 * @nents: Number of SG entries
456 * @buf: Where to copy from
457 * @buflen: The number of bytes to copy
458 *
459 * Returns the number of copied bytes.
460 *
461 **/
sg_copy_from_buffer(struct scatterlist * sgl,unsigned int nents,void * buf,size_t buflen)462 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
463 void *buf, size_t buflen)
464 {
465 return sg_copy_buffer(sgl, nents, buf, buflen, 0);
466 }
467 EXPORT_SYMBOL(sg_copy_from_buffer);
468
469 /**
470 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
471 * @sgl: The SG list
472 * @nents: Number of SG entries
473 * @buf: Where to copy to
474 * @buflen: The number of bytes to copy
475 *
476 * Returns the number of copied bytes.
477 *
478 **/
sg_copy_to_buffer(struct scatterlist * sgl,unsigned int nents,void * buf,size_t buflen)479 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
480 void *buf, size_t buflen)
481 {
482 return sg_copy_buffer(sgl, nents, buf, buflen, 1);
483 }
484 EXPORT_SYMBOL(sg_copy_to_buffer);
485