Root/lib/scatterlist.c

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/slab.h>
11#include <linux/scatterlist.h>
12#include <linux/highmem.h>
13#include <linux/kmemleak.h>
14
15/**
16 * sg_next - return the next scatterlist entry in a list
17 * @sg: The current sg entry
18 *
19 * Description:
20 * Usually the next entry will be @sg@ + 1, but if this sg element is part
21 * of a chained scatterlist, it could jump to the start of a new
22 * scatterlist array.
23 *
24 **/
25struct scatterlist *sg_next(struct scatterlist *sg)
26{
27#ifdef CONFIG_DEBUG_SG
28    BUG_ON(sg->sg_magic != SG_MAGIC);
29#endif
30    if (sg_is_last(sg))
31        return NULL;
32
33    sg++;
34    if (unlikely(sg_is_chain(sg)))
35        sg = sg_chain_ptr(sg);
36
37    return sg;
38}
39EXPORT_SYMBOL(sg_next);
40
41/**
42 * sg_last - return the last scatterlist entry in a list
43 * @sgl: First entry in the scatterlist
44 * @nents: Number of entries in the scatterlist
45 *
46 * Description:
47 * Should only be used casually, it (currently) scans the entire list
48 * to get the last entry.
49 *
50 * Note that the @sgl@ pointer passed in need not be the first one,
51 * the important bit is that @nents@ denotes the number of entries that
52 * exist from @sgl@.
53 *
54 **/
55struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
56{
57#ifndef ARCH_HAS_SG_CHAIN
58    struct scatterlist *ret = &sgl[nents - 1];
59#else
60    struct scatterlist *sg, *ret = NULL;
61    unsigned int i;
62
63    for_each_sg(sgl, sg, nents, i)
64        ret = sg;
65
66#endif
67#ifdef CONFIG_DEBUG_SG
68    BUG_ON(sgl[0].sg_magic != SG_MAGIC);
69    BUG_ON(!sg_is_last(ret));
70#endif
71    return ret;
72}
73EXPORT_SYMBOL(sg_last);
74
75/**
76 * sg_init_table - Initialize SG table
77 * @sgl: The SG table
78 * @nents: Number of entries in table
79 *
80 * Notes:
81 * If this is part of a chained sg table, sg_mark_end() should be
82 * used only on the last table part.
83 *
84 **/
85void sg_init_table(struct scatterlist *sgl, unsigned int nents)
86{
87    memset(sgl, 0, sizeof(*sgl) * nents);
88#ifdef CONFIG_DEBUG_SG
89    {
90        unsigned int i;
91        for (i = 0; i < nents; i++)
92            sgl[i].sg_magic = SG_MAGIC;
93    }
94#endif
95    sg_mark_end(&sgl[nents - 1]);
96}
97EXPORT_SYMBOL(sg_init_table);
98
99/**
100 * sg_init_one - Initialize a single entry sg list
101 * @sg: SG entry
102 * @buf: Virtual address for IO
103 * @buflen: IO length
104 *
105 **/
106void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
107{
108    sg_init_table(sg, 1);
109    sg_set_buf(sg, buf, buflen);
110}
111EXPORT_SYMBOL(sg_init_one);
112
113/*
114 * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
115 * helpers.
116 */
117static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
118{
119    if (nents == SG_MAX_SINGLE_ALLOC) {
120        /*
121         * Kmemleak doesn't track page allocations as they are not
122         * commonly used (in a raw form) for kernel data structures.
123         * As we chain together a list of pages and then a normal
124         * kmalloc (tracked by kmemleak), in order to for that last
125         * allocation not to become decoupled (and thus a
126         * false-positive) we need to inform kmemleak of all the
127         * intermediate allocations.
128         */
129        void *ptr = (void *) __get_free_page(gfp_mask);
130        kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask);
131        return ptr;
132    } else
133        return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
134}
135
136static void sg_kfree(struct scatterlist *sg, unsigned int nents)
137{
138    if (nents == SG_MAX_SINGLE_ALLOC) {
139        kmemleak_free(sg);
140        free_page((unsigned long) sg);
141    } else
142        kfree(sg);
143}
144
145/**
146 * __sg_free_table - Free a previously mapped sg table
147 * @table: The sg table header to use
148 * @max_ents: The maximum number of entries per single scatterlist
149 * @free_fn: Free function
150 *
151 * Description:
152 * Free an sg table previously allocated and setup with
153 * __sg_alloc_table(). The @max_ents value must be identical to
154 * that previously used with __sg_alloc_table().
155 *
156 **/
157void __sg_free_table(struct sg_table *table, unsigned int max_ents,
158             sg_free_fn *free_fn)
159{
160    struct scatterlist *sgl, *next;
161
162    if (unlikely(!table->sgl))
163        return;
164
165    sgl = table->sgl;
166    while (table->orig_nents) {
167        unsigned int alloc_size = table->orig_nents;
168        unsigned int sg_size;
169
170        /*
171         * If we have more than max_ents segments left,
172         * then assign 'next' to the sg table after the current one.
173         * sg_size is then one less than alloc size, since the last
174         * element is the chain pointer.
175         */
176        if (alloc_size > max_ents) {
177            next = sg_chain_ptr(&sgl[max_ents - 1]);
178            alloc_size = max_ents;
179            sg_size = alloc_size - 1;
180        } else {
181            sg_size = alloc_size;
182            next = NULL;
183        }
184
185        table->orig_nents -= sg_size;
186        free_fn(sgl, alloc_size);
187        sgl = next;
188    }
189
190    table->sgl = NULL;
191}
192EXPORT_SYMBOL(__sg_free_table);
193
194/**
195 * sg_free_table - Free a previously allocated sg table
196 * @table: The mapped sg table header
197 *
198 **/
199void sg_free_table(struct sg_table *table)
200{
201    __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
202}
203EXPORT_SYMBOL(sg_free_table);
204
205/**
206 * __sg_alloc_table - Allocate and initialize an sg table with given allocator
207 * @table: The sg table header to use
208 * @nents: Number of entries in sg list
209 * @max_ents: The maximum number of entries the allocator returns per call
210 * @gfp_mask: GFP allocation mask
211 * @alloc_fn: Allocator to use
212 *
213 * Description:
214 * This function returns a @table @nents long. The allocator is
215 * defined to return scatterlist chunks of maximum size @max_ents.
216 * Thus if @nents is bigger than @max_ents, the scatterlists will be
217 * chained in units of @max_ents.
218 *
219 * Notes:
220 * If this function returns non-0 (eg failure), the caller must call
221 * __sg_free_table() to cleanup any leftover allocations.
222 *
223 **/
224int __sg_alloc_table(struct sg_table *table, unsigned int nents,
225             unsigned int max_ents, gfp_t gfp_mask,
226             sg_alloc_fn *alloc_fn)
227{
228    struct scatterlist *sg, *prv;
229    unsigned int left;
230
231#ifndef ARCH_HAS_SG_CHAIN
232    BUG_ON(nents > max_ents);
233#endif
234
235    memset(table, 0, sizeof(*table));
236
237    left = nents;
238    prv = NULL;
239    do {
240        unsigned int sg_size, alloc_size = left;
241
242        if (alloc_size > max_ents) {
243            alloc_size = max_ents;
244            sg_size = alloc_size - 1;
245        } else
246            sg_size = alloc_size;
247
248        left -= sg_size;
249
250        sg = alloc_fn(alloc_size, gfp_mask);
251        if (unlikely(!sg)) {
252            /*
253             * Adjust entry count to reflect that the last
254             * entry of the previous table won't be used for
255             * linkage. Without this, sg_kfree() may get
256             * confused.
257             */
258            if (prv)
259                table->nents = ++table->orig_nents;
260
261             return -ENOMEM;
262        }
263
264        sg_init_table(sg, alloc_size);
265        table->nents = table->orig_nents += sg_size;
266
267        /*
268         * If this is the first mapping, assign the sg table header.
269         * If this is not the first mapping, chain previous part.
270         */
271        if (prv)
272            sg_chain(prv, max_ents, sg);
273        else
274            table->sgl = sg;
275
276        /*
277         * If no more entries after this one, mark the end
278         */
279        if (!left)
280            sg_mark_end(&sg[sg_size - 1]);
281
282        /*
283         * only really needed for mempool backed sg allocations (like
284         * SCSI), a possible improvement here would be to pass the
285         * table pointer into the allocator and let that clear these
286         * flags
287         */
288        gfp_mask &= ~__GFP_WAIT;
289        gfp_mask |= __GFP_HIGH;
290        prv = sg;
291    } while (left);
292
293    return 0;
294}
295EXPORT_SYMBOL(__sg_alloc_table);
296
297/**
298 * sg_alloc_table - Allocate and initialize an sg table
299 * @table: The sg table header to use
300 * @nents: Number of entries in sg list
301 * @gfp_mask: GFP allocation mask
302 *
303 * Description:
304 * Allocate and initialize an sg table. If @nents@ is larger than
305 * SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
306 *
307 **/
308int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
309{
310    int ret;
311
312    ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
313                   gfp_mask, sg_kmalloc);
314    if (unlikely(ret))
315        __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
316
317    return ret;
318}
319EXPORT_SYMBOL(sg_alloc_table);
320
321/**
322 * sg_miter_start - start mapping iteration over a sg list
323 * @miter: sg mapping iter to be started
324 * @sgl: sg list to iterate over
325 * @nents: number of sg entries
326 *
327 * Description:
328 * Starts mapping iterator @miter.
329 *
330 * Context:
331 * Don't care.
332 */
333void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
334            unsigned int nents, unsigned int flags)
335{
336    memset(miter, 0, sizeof(struct sg_mapping_iter));
337
338    miter->__sg = sgl;
339    miter->__nents = nents;
340    miter->__offset = 0;
341    WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
342    miter->__flags = flags;
343}
344EXPORT_SYMBOL(sg_miter_start);
345
346/**
347 * sg_miter_next - proceed mapping iterator to the next mapping
348 * @miter: sg mapping iter to proceed
349 *
350 * Description:
351 * Proceeds @miter@ to the next mapping. @miter@ should have been
352 * started using sg_miter_start(). On successful return,
353 * @miter@->page, @miter@->addr and @miter@->length point to the
354 * current mapping.
355 *
356 * Context:
357 * IRQ disabled if SG_MITER_ATOMIC. IRQ must stay disabled till
358 * @miter@ is stopped. May sleep if !SG_MITER_ATOMIC.
359 *
360 * Returns:
361 * true if @miter contains the next mapping. false if end of sg
362 * list is reached.
363 */
364bool sg_miter_next(struct sg_mapping_iter *miter)
365{
366    unsigned int off, len;
367
368    /* check for end and drop resources from the last iteration */
369    if (!miter->__nents)
370        return false;
371
372    sg_miter_stop(miter);
373
374    /* get to the next sg if necessary. __offset is adjusted by stop */
375    while (miter->__offset == miter->__sg->length) {
376        if (--miter->__nents) {
377            miter->__sg = sg_next(miter->__sg);
378            miter->__offset = 0;
379        } else
380            return false;
381    }
382
383    /* map the next page */
384    off = miter->__sg->offset + miter->__offset;
385    len = miter->__sg->length - miter->__offset;
386
387    miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
388    off &= ~PAGE_MASK;
389    miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
390    miter->consumed = miter->length;
391
392    if (miter->__flags & SG_MITER_ATOMIC)
393        miter->addr = kmap_atomic(miter->page, KM_BIO_SRC_IRQ) + off;
394    else
395        miter->addr = kmap(miter->page) + off;
396
397    return true;
398}
399EXPORT_SYMBOL(sg_miter_next);
400
401/**
402 * sg_miter_stop - stop mapping iteration
403 * @miter: sg mapping iter to be stopped
404 *
405 * Description:
406 * Stops mapping iterator @miter. @miter should have been started
407 * started using sg_miter_start(). A stopped iteration can be
408 * resumed by calling sg_miter_next() on it. This is useful when
409 * resources (kmap) need to be released during iteration.
410 *
411 * Context:
412 * IRQ disabled if the SG_MITER_ATOMIC is set. Don't care otherwise.
413 */
414void sg_miter_stop(struct sg_mapping_iter *miter)
415{
416    WARN_ON(miter->consumed > miter->length);
417
418    /* drop resources from the last iteration */
419    if (miter->addr) {
420        miter->__offset += miter->consumed;
421
422        if (miter->__flags & SG_MITER_TO_SG)
423            flush_kernel_dcache_page(miter->page);
424
425        if (miter->__flags & SG_MITER_ATOMIC) {
426            WARN_ON(!irqs_disabled());
427            kunmap_atomic(miter->addr, KM_BIO_SRC_IRQ);
428        } else
429            kunmap(miter->page);
430
431        miter->page = NULL;
432        miter->addr = NULL;
433        miter->length = 0;
434        miter->consumed = 0;
435    }
436}
437EXPORT_SYMBOL(sg_miter_stop);
438
439/**
440 * sg_copy_buffer - Copy data between a linear buffer and an SG list
441 * @sgl: The SG list
442 * @nents: Number of SG entries
443 * @buf: Where to copy from
444 * @buflen: The number of bytes to copy
445 * @to_buffer: transfer direction (non zero == from an sg list to a
446 * buffer, 0 == from a buffer to an sg list
447 *
448 * Returns the number of copied bytes.
449 *
450 **/
451static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
452                 void *buf, size_t buflen, int to_buffer)
453{
454    unsigned int offset = 0;
455    struct sg_mapping_iter miter;
456    unsigned long flags;
457    unsigned int sg_flags = SG_MITER_ATOMIC;
458
459    if (to_buffer)
460        sg_flags |= SG_MITER_FROM_SG;
461    else
462        sg_flags |= SG_MITER_TO_SG;
463
464    sg_miter_start(&miter, sgl, nents, sg_flags);
465
466    local_irq_save(flags);
467
468    while (sg_miter_next(&miter) && offset < buflen) {
469        unsigned int len;
470
471        len = min(miter.length, buflen - offset);
472
473        if (to_buffer)
474            memcpy(buf + offset, miter.addr, len);
475        else
476            memcpy(miter.addr, buf + offset, len);
477
478        offset += len;
479    }
480
481    sg_miter_stop(&miter);
482
483    local_irq_restore(flags);
484    return offset;
485}
486
487/**
488 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
489 * @sgl: The SG list
490 * @nents: Number of SG entries
491 * @buf: Where to copy from
492 * @buflen: The number of bytes to copy
493 *
494 * Returns the number of copied bytes.
495 *
496 **/
497size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
498               void *buf, size_t buflen)
499{
500    return sg_copy_buffer(sgl, nents, buf, buflen, 0);
501}
502EXPORT_SYMBOL(sg_copy_from_buffer);
503
504/**
505 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
506 * @sgl: The SG list
507 * @nents: Number of SG entries
508 * @buf: Where to copy to
509 * @buflen: The number of bytes to copy
510 *
511 * Returns the number of copied bytes.
512 *
513 **/
514size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
515             void *buf, size_t buflen)
516{
517    return sg_copy_buffer(sgl, nents, buf, buflen, 1);
518}
519EXPORT_SYMBOL(sg_copy_to_buffer);
520

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