linux/lib/scatterlist.c
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   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/export.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_nents - return total count of entries in scatterlist
  43 * @sg:         The scatterlist
  44 *
  45 * Description:
  46 * Allows to know how many entries are in sg, taking into acount
  47 * chaining as well
  48 *
  49 **/
  50int sg_nents(struct scatterlist *sg)
  51{
  52        int nents;
  53        for (nents = 0; sg; sg = sg_next(sg))
  54                nents++;
  55        return nents;
  56}
  57EXPORT_SYMBOL(sg_nents);
  58
  59
  60/**
  61 * sg_last - return the last scatterlist entry in a list
  62 * @sgl:        First entry in the scatterlist
  63 * @nents:      Number of entries in the scatterlist
  64 *
  65 * Description:
  66 *   Should only be used casually, it (currently) scans the entire list
  67 *   to get the last entry.
  68 *
  69 *   Note that the @sgl@ pointer passed in need not be the first one,
  70 *   the important bit is that @nents@ denotes the number of entries that
  71 *   exist from @sgl@.
  72 *
  73 **/
  74struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
  75{
  76#ifndef ARCH_HAS_SG_CHAIN
  77        struct scatterlist *ret = &sgl[nents - 1];
  78#else
  79        struct scatterlist *sg, *ret = NULL;
  80        unsigned int i;
  81
  82        for_each_sg(sgl, sg, nents, i)
  83                ret = sg;
  84
  85#endif
  86#ifdef CONFIG_DEBUG_SG
  87        BUG_ON(sgl[0].sg_magic != SG_MAGIC);
  88        BUG_ON(!sg_is_last(ret));
  89#endif
  90        return ret;
  91}
  92EXPORT_SYMBOL(sg_last);
  93
  94/**
  95 * sg_init_table - Initialize SG table
  96 * @sgl:           The SG table
  97 * @nents:         Number of entries in table
  98 *
  99 * Notes:
 100 *   If this is part of a chained sg table, sg_mark_end() should be
 101 *   used only on the last table part.
 102 *
 103 **/
 104void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 105{
 106        memset(sgl, 0, sizeof(*sgl) * nents);
 107#ifdef CONFIG_DEBUG_SG
 108        {
 109                unsigned int i;
 110                for (i = 0; i < nents; i++)
 111                        sgl[i].sg_magic = SG_MAGIC;
 112        }
 113#endif
 114        sg_mark_end(&sgl[nents - 1]);
 115}
 116EXPORT_SYMBOL(sg_init_table);
 117
 118/**
 119 * sg_init_one - Initialize a single entry sg list
 120 * @sg:          SG entry
 121 * @buf:         Virtual address for IO
 122 * @buflen:      IO length
 123 *
 124 **/
 125void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
 126{
 127        sg_init_table(sg, 1);
 128        sg_set_buf(sg, buf, buflen);
 129}
 130EXPORT_SYMBOL(sg_init_one);
 131
 132/*
 133 * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
 134 * helpers.
 135 */
 136static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
 137{
 138        if (nents == SG_MAX_SINGLE_ALLOC) {
 139                /*
 140                 * Kmemleak doesn't track page allocations as they are not
 141                 * commonly used (in a raw form) for kernel data structures.
 142                 * As we chain together a list of pages and then a normal
 143                 * kmalloc (tracked by kmemleak), in order to for that last
 144                 * allocation not to become decoupled (and thus a
 145                 * false-positive) we need to inform kmemleak of all the
 146                 * intermediate allocations.
 147                 */
 148                void *ptr = (void *) __get_free_page(gfp_mask);
 149                kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask);
 150                return ptr;
 151        } else
 152                return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
 153}
 154
 155static void sg_kfree(struct scatterlist *sg, unsigned int nents)
 156{
 157        if (nents == SG_MAX_SINGLE_ALLOC) {
 158                kmemleak_free(sg);
 159                free_page((unsigned long) sg);
 160        } else
 161                kfree(sg);
 162}
 163
 164/**
 165 * __sg_free_table - Free a previously mapped sg table
 166 * @table:      The sg table header to use
 167 * @max_ents:   The maximum number of entries per single scatterlist
 168 * @free_fn:    Free function
 169 *
 170 *  Description:
 171 *    Free an sg table previously allocated and setup with
 172 *    __sg_alloc_table().  The @max_ents value must be identical to
 173 *    that previously used with __sg_alloc_table().
 174 *
 175 **/
 176void __sg_free_table(struct sg_table *table, unsigned int max_ents,
 177                     sg_free_fn *free_fn)
 178{
 179        struct scatterlist *sgl, *next;
 180
 181        if (unlikely(!table->sgl))
 182                return;
 183
 184        sgl = table->sgl;
 185        while (table->orig_nents) {
 186                unsigned int alloc_size = table->orig_nents;
 187                unsigned int sg_size;
 188
 189                /*
 190                 * If we have more than max_ents segments left,
 191                 * then assign 'next' to the sg table after the current one.
 192                 * sg_size is then one less than alloc size, since the last
 193                 * element is the chain pointer.
 194                 */
 195                if (alloc_size > max_ents) {
 196                        next = sg_chain_ptr(&sgl[max_ents - 1]);
 197                        alloc_size = max_ents;
 198                        sg_size = alloc_size - 1;
 199                } else {
 200                        sg_size = alloc_size;
 201                        next = NULL;
 202                }
 203
 204                table->orig_nents -= sg_size;
 205                free_fn(sgl, alloc_size);
 206                sgl = next;
 207        }
 208
 209        table->sgl = NULL;
 210}
 211EXPORT_SYMBOL(__sg_free_table);
 212
 213/**
 214 * sg_free_table - Free a previously allocated sg table
 215 * @table:      The mapped sg table header
 216 *
 217 **/
 218void sg_free_table(struct sg_table *table)
 219{
 220        __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 221}
 222EXPORT_SYMBOL(sg_free_table);
 223
 224/**
 225 * __sg_alloc_table - Allocate and initialize an sg table with given allocator
 226 * @table:      The sg table header to use
 227 * @nents:      Number of entries in sg list
 228 * @max_ents:   The maximum number of entries the allocator returns per call
 229 * @gfp_mask:   GFP allocation mask
 230 * @alloc_fn:   Allocator to use
 231 *
 232 * Description:
 233 *   This function returns a @table @nents long. The allocator is
 234 *   defined to return scatterlist chunks of maximum size @max_ents.
 235 *   Thus if @nents is bigger than @max_ents, the scatterlists will be
 236 *   chained in units of @max_ents.
 237 *
 238 * Notes:
 239 *   If this function returns non-0 (eg failure), the caller must call
 240 *   __sg_free_table() to cleanup any leftover allocations.
 241 *
 242 **/
 243int __sg_alloc_table(struct sg_table *table, unsigned int nents,
 244                     unsigned int max_ents, gfp_t gfp_mask,
 245                     sg_alloc_fn *alloc_fn)
 246{
 247        struct scatterlist *sg, *prv;
 248        unsigned int left;
 249
 250#ifndef ARCH_HAS_SG_CHAIN
 251        BUG_ON(nents > max_ents);
 252#endif
 253
 254        memset(table, 0, sizeof(*table));
 255
 256        left = nents;
 257        prv = NULL;
 258        do {
 259                unsigned int sg_size, alloc_size = left;
 260
 261                if (alloc_size > max_ents) {
 262                        alloc_size = max_ents;
 263                        sg_size = alloc_size - 1;
 264                } else
 265                        sg_size = alloc_size;
 266
 267                left -= sg_size;
 268
 269                sg = alloc_fn(alloc_size, gfp_mask);
 270                if (unlikely(!sg)) {
 271                        /*
 272                         * Adjust entry count to reflect that the last
 273                         * entry of the previous table won't be used for
 274                         * linkage.  Without this, sg_kfree() may get
 275                         * confused.
 276                         */
 277                        if (prv)
 278                                table->nents = ++table->orig_nents;
 279
 280                        return -ENOMEM;
 281                }
 282
 283                sg_init_table(sg, alloc_size);
 284                table->nents = table->orig_nents += sg_size;
 285
 286                /*
 287                 * If this is the first mapping, assign the sg table header.
 288                 * If this is not the first mapping, chain previous part.
 289                 */
 290                if (prv)
 291                        sg_chain(prv, max_ents, sg);
 292                else
 293                        table->sgl = sg;
 294
 295                /*
 296                 * If no more entries after this one, mark the end
 297                 */
 298                if (!left)
 299                        sg_mark_end(&sg[sg_size - 1]);
 300
 301                prv = sg;
 302        } while (left);
 303
 304        return 0;
 305}
 306EXPORT_SYMBOL(__sg_alloc_table);
 307
 308/**
 309 * sg_alloc_table - Allocate and initialize an sg table
 310 * @table:      The sg table header to use
 311 * @nents:      Number of entries in sg list
 312 * @gfp_mask:   GFP allocation mask
 313 *
 314 *  Description:
 315 *    Allocate and initialize an sg table. If @nents@ is larger than
 316 *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
 317 *
 318 **/
 319int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
 320{
 321        int ret;
 322
 323        ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
 324                               gfp_mask, sg_kmalloc);
 325        if (unlikely(ret))
 326                __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 327
 328        return ret;
 329}
 330EXPORT_SYMBOL(sg_alloc_table);
 331
 332/**
 333 * sg_alloc_table_from_pages - Allocate and initialize an sg table from
 334 *                             an array of pages
 335 * @sgt:        The sg table header to use
 336 * @pages:      Pointer to an array of page pointers
 337 * @n_pages:    Number of pages in the pages array
 338 * @offset:     Offset from start of the first page to the start of a buffer
 339 * @size:       Number of valid bytes in the buffer (after offset)
 340 * @gfp_mask:   GFP allocation mask
 341 *
 342 *  Description:
 343 *    Allocate and initialize an sg table from a list of pages. Contiguous
 344 *    ranges of the pages are squashed into a single scatterlist node. A user
 345 *    may provide an offset at a start and a size of valid data in a buffer
 346 *    specified by the page array. The returned sg table is released by
 347 *    sg_free_table.
 348 *
 349 * Returns:
 350 *   0 on success, negative error on failure
 351 */
 352int sg_alloc_table_from_pages(struct sg_table *sgt,
 353        struct page **pages, unsigned int n_pages,
 354        unsigned long offset, unsigned long size,
 355        gfp_t gfp_mask)
 356{
 357        unsigned int chunks;
 358        unsigned int i;
 359        unsigned int cur_page;
 360        int ret;
 361        struct scatterlist *s;
 362
 363        /* compute number of contiguous chunks */
 364        chunks = 1;
 365        for (i = 1; i < n_pages; ++i)
 366                if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
 367                        ++chunks;
 368
 369        ret = sg_alloc_table(sgt, chunks, gfp_mask);
 370        if (unlikely(ret))
 371                return ret;
 372
 373        /* merging chunks and putting them into the scatterlist */
 374        cur_page = 0;
 375        for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
 376                unsigned long chunk_size;
 377                unsigned int j;
 378
 379                /* look for the end of the current chunk */
 380                for (j = cur_page + 1; j < n_pages; ++j)
 381                        if (page_to_pfn(pages[j]) !=
 382                            page_to_pfn(pages[j - 1]) + 1)
 383                                break;
 384
 385                chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
 386                sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
 387                size -= chunk_size;
 388                offset = 0;
 389                cur_page = j;
 390        }
 391
 392        return 0;
 393}
 394EXPORT_SYMBOL(sg_alloc_table_from_pages);
 395
 396/**
 397 * sg_miter_start - start mapping iteration over a sg list
 398 * @miter: sg mapping iter to be started
 399 * @sgl: sg list to iterate over
 400 * @nents: number of sg entries
 401 *
 402 * Description:
 403 *   Starts mapping iterator @miter.
 404 *
 405 * Context:
 406 *   Don't care.
 407 */
 408void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 409                    unsigned int nents, unsigned int flags)
 410{
 411        memset(miter, 0, sizeof(struct sg_mapping_iter));
 412
 413        miter->__sg = sgl;
 414        miter->__nents = nents;
 415        miter->__offset = 0;
 416        WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
 417        miter->__flags = flags;
 418}
 419EXPORT_SYMBOL(sg_miter_start);
 420
 421/**
 422 * sg_miter_next - proceed mapping iterator to the next mapping
 423 * @miter: sg mapping iter to proceed
 424 *
 425 * Description:
 426 *   Proceeds @miter to the next mapping.  @miter should have been started
 427 *   using sg_miter_start().  On successful return, @miter->page,
 428 *   @miter->addr and @miter->length point to the current mapping.
 429 *
 430 * Context:
 431 *   Preemption disabled if SG_MITER_ATOMIC.  Preemption must stay disabled
 432 *   till @miter is stopped.  May sleep if !SG_MITER_ATOMIC.
 433 *
 434 * Returns:
 435 *   true if @miter contains the next mapping.  false if end of sg
 436 *   list is reached.
 437 */
 438bool sg_miter_next(struct sg_mapping_iter *miter)
 439{
 440        unsigned int off, len;
 441
 442        /* check for end and drop resources from the last iteration */
 443        if (!miter->__nents)
 444                return false;
 445
 446        sg_miter_stop(miter);
 447
 448        /* get to the next sg if necessary.  __offset is adjusted by stop */
 449        while (miter->__offset == miter->__sg->length) {
 450                if (--miter->__nents) {
 451                        miter->__sg = sg_next(miter->__sg);
 452                        miter->__offset = 0;
 453                } else
 454                        return false;
 455        }
 456
 457        /* map the next page */
 458        off = miter->__sg->offset + miter->__offset;
 459        len = miter->__sg->length - miter->__offset;
 460
 461        miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
 462        off &= ~PAGE_MASK;
 463        miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
 464        miter->consumed = miter->length;
 465
 466        if (miter->__flags & SG_MITER_ATOMIC)
 467                miter->addr = kmap_atomic(miter->page) + off;
 468        else
 469                miter->addr = kmap(miter->page) + off;
 470
 471        return true;
 472}
 473EXPORT_SYMBOL(sg_miter_next);
 474
 475/**
 476 * sg_miter_stop - stop mapping iteration
 477 * @miter: sg mapping iter to be stopped
 478 *
 479 * Description:
 480 *   Stops mapping iterator @miter.  @miter should have been started
 481 *   started using sg_miter_start().  A stopped iteration can be
 482 *   resumed by calling sg_miter_next() on it.  This is useful when
 483 *   resources (kmap) need to be released during iteration.
 484 *
 485 * Context:
 486 *   Preemption disabled if the SG_MITER_ATOMIC is set.  Don't care
 487 *   otherwise.
 488 */
 489void sg_miter_stop(struct sg_mapping_iter *miter)
 490{
 491        WARN_ON(miter->consumed > miter->length);
 492
 493        /* drop resources from the last iteration */
 494        if (miter->addr) {
 495                miter->__offset += miter->consumed;
 496
 497                if (miter->__flags & SG_MITER_TO_SG)
 498                        flush_kernel_dcache_page(miter->page);
 499
 500                if (miter->__flags & SG_MITER_ATOMIC) {
 501                        WARN_ON_ONCE(preemptible());
 502                        kunmap_atomic(miter->addr);
 503                } else
 504                        kunmap(miter->page);
 505
 506                miter->page = NULL;
 507                miter->addr = NULL;
 508                miter->length = 0;
 509                miter->consumed = 0;
 510        }
 511}
 512EXPORT_SYMBOL(sg_miter_stop);
 513
 514/**
 515 * sg_copy_buffer - Copy data between a linear buffer and an SG list
 516 * @sgl:                 The SG list
 517 * @nents:               Number of SG entries
 518 * @buf:                 Where to copy from
 519 * @buflen:              The number of bytes to copy
 520 * @to_buffer:           transfer direction (non zero == from an sg list to a
 521 *                       buffer, 0 == from a buffer to an sg list
 522 *
 523 * Returns the number of copied bytes.
 524 *
 525 **/
 526static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 527                             void *buf, size_t buflen, int to_buffer)
 528{
 529        unsigned int offset = 0;
 530        struct sg_mapping_iter miter;
 531        unsigned long flags;
 532        unsigned int sg_flags = SG_MITER_ATOMIC;
 533
 534        if (to_buffer)
 535                sg_flags |= SG_MITER_FROM_SG;
 536        else
 537                sg_flags |= SG_MITER_TO_SG;
 538
 539        sg_miter_start(&miter, sgl, nents, sg_flags);
 540
 541        local_irq_save(flags);
 542
 543        while (sg_miter_next(&miter) && offset < buflen) {
 544                unsigned int len;
 545
 546                len = min(miter.length, buflen - offset);
 547
 548                if (to_buffer)
 549                        memcpy(buf + offset, miter.addr, len);
 550                else
 551                        memcpy(miter.addr, buf + offset, len);
 552
 553                offset += len;
 554        }
 555
 556        sg_miter_stop(&miter);
 557
 558        local_irq_restore(flags);
 559        return offset;
 560}
 561
 562/**
 563 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
 564 * @sgl:                 The SG list
 565 * @nents:               Number of SG entries
 566 * @buf:                 Where to copy from
 567 * @buflen:              The number of bytes to copy
 568 *
 569 * Returns the number of copied bytes.
 570 *
 571 **/
 572size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 573                           void *buf, size_t buflen)
 574{
 575        return sg_copy_buffer(sgl, nents, buf, buflen, 0);
 576}
 577EXPORT_SYMBOL(sg_copy_from_buffer);
 578
 579/**
 580 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
 581 * @sgl:                 The SG list
 582 * @nents:               Number of SG entries
 583 * @buf:                 Where to copy to
 584 * @buflen:              The number of bytes to copy
 585 *
 586 * Returns the number of copied bytes.
 587 *
 588 **/
 589size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 590                         void *buf, size_t buflen)
 591{
 592        return sg_copy_buffer(sgl, nents, buf, buflen, 1);
 593}
 594EXPORT_SYMBOL(sg_copy_to_buffer);
 595
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