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/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  **/
  25 struct 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 }
  39 EXPORT_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  **/
  50 int sg_nents(struct scatterlist *sg)
  51 {
  52         int nents;
  53         for (nents = 0; sg; sg = sg_next(sg))
  54                 nents++;
  55         return nents;
  56 }
  57 EXPORT_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  **/
  74 struct 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 }
  92 EXPORT_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  **/
 104 void 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 }
 116 EXPORT_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  **/
 125 void 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 }
 130 EXPORT_SYMBOL(sg_init_one);
 131
 132 /*
 133  * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
 134  * helpers.
 135  */
 136 static 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
 155 static 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  **/
 176 void __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 }
 211 EXPORT_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  **/
 218 void sg_free_table(struct sg_table *table)
 219 {
 220         __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 221 }
 222 EXPORT_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  **/
 243 int __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         if (WARN_ON_ONCE(nents > max_ents))
 252                 return -EINVAL;
 253 #endif
 254
 255         memset(table, 0, sizeof(*table));
 256
 257         left = nents;
 258         prv = NULL;
 259         do {
 260                 unsigned int sg_size, alloc_size = left;
 261
 262                 if (alloc_size > max_ents) {
 263                         alloc_size = max_ents;
 264                         sg_size = alloc_size - 1;
 265                 } else
 266                         sg_size = alloc_size;
 267
 268                 left -= sg_size;
 269
 270                 sg = alloc_fn(alloc_size, gfp_mask);
 271                 if (unlikely(!sg)) {
 272                         /*
 273                          * Adjust entry count to reflect that the last
 274                          * entry of the previous table won't be used for
 275                          * linkage.  Without this, sg_kfree() may get
 276                          * confused.
 277                          */
 278                         if (prv)
 279                                 table->nents = ++table->orig_nents;
 280
 281                         return -ENOMEM;
 282                 }
 283
 284                 sg_init_table(sg, alloc_size);
 285                 table->nents = table->orig_nents += sg_size;
 286
 287                 /*
 288                  * If this is the first mapping, assign the sg table header.
 289                  * If this is not the first mapping, chain previous part.
 290                  */
 291                 if (prv)
 292                         sg_chain(prv, max_ents, sg);
 293                 else
 294                         table->sgl = sg;
 295
 296                 /*
 297                  * If no more entries after this one, mark the end
 298                  */
 299                 if (!left)
 300                         sg_mark_end(&sg[sg_size - 1]);
 301
 302                 prv = sg;
 303         } while (left);
 304
 305         return 0;
 306 }
 307 EXPORT_SYMBOL(__sg_alloc_table);
 308
 309 /**
 310  * sg_alloc_table - Allocate and initialize an sg table
 311  * @table:      The sg table header to use
 312  * @nents:      Number of entries in sg list
 313  * @gfp_mask:   GFP allocation mask
 314  *
 315  *  Description:
 316  *    Allocate and initialize an sg table. If @nents@ is larger than
 317  *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
 318  *
 319  **/
 320 int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
 321 {
 322         int ret;
 323
 324         ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
 325                                gfp_mask, sg_kmalloc);
 326         if (unlikely(ret))
 327                 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 328
 329         return ret;
 330 }
 331 EXPORT_SYMBOL(sg_alloc_table);
 332
 333 /**
 334  * sg_alloc_table_from_pages - Allocate and initialize an sg table from
 335  *                             an array of pages
 336  * @sgt:        The sg table header to use
 337  * @pages:      Pointer to an array of page pointers
 338  * @n_pages:    Number of pages in the pages array
 339  * @offset:     Offset from start of the first page to the start of a buffer
 340  * @size:       Number of valid bytes in the buffer (after offset)
 341  * @gfp_mask:   GFP allocation mask
 342  *
 343  *  Description:
 344  *    Allocate and initialize an sg table from a list of pages. Contiguous
 345  *    ranges of the pages are squashed into a single scatterlist node. A user
 346  *    may provide an offset at a start and a size of valid data in a buffer
 347  *    specified by the page array. The returned sg table is released by
 348  *    sg_free_table.
 349  *
 350  * Returns:
 351  *   0 on success, negative error on failure
 352  */
 353 int sg_alloc_table_from_pages(struct sg_table *sgt,
 354         struct page **pages, unsigned int n_pages,
 355         unsigned long offset, unsigned long size,
 356         gfp_t gfp_mask)
 357 {
 358         unsigned int chunks;
 359         unsigned int i;
 360         unsigned int cur_page;
 361         int ret;
 362         struct scatterlist *s;
 363
 364         /* compute number of contiguous chunks */
 365         chunks = 1;
 366         for (i = 1; i < n_pages; ++i)
 367                 if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
 368                         ++chunks;
 369
 370         ret = sg_alloc_table(sgt, chunks, gfp_mask);
 371         if (unlikely(ret))
 372                 return ret;
 373
 374         /* merging chunks and putting them into the scatterlist */
 375         cur_page = 0;
 376         for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
 377                 unsigned long chunk_size;
 378                 unsigned int j;
 379
 380                 /* look for the end of the current chunk */
 381                 for (j = cur_page + 1; j < n_pages; ++j)
 382                         if (page_to_pfn(pages[j]) !=
 383                             page_to_pfn(pages[j - 1]) + 1)
 384                                 break;
 385
 386                 chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
 387                 sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
 388                 size -= chunk_size;
 389                 offset = 0;
 390                 cur_page = j;
 391         }
 392
 393         return 0;
 394 }
 395 EXPORT_SYMBOL(sg_alloc_table_from_pages);
 396
 397 /**
 398  * sg_miter_start - start mapping iteration over a sg list
 399  * @miter: sg mapping iter to be started
 400  * @sgl: sg list to iterate over
 401  * @nents: number of sg entries
 402  *
 403  * Description:
 404  *   Starts mapping iterator @miter.
 405  *
 406  * Context:
 407  *   Don't care.
 408  */
 409 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 410                     unsigned int nents, unsigned int flags)
 411 {
 412         memset(miter, 0, sizeof(struct sg_mapping_iter));
 413
 414         miter->__sg = sgl;
 415         miter->__nents = nents;
 416         miter->__offset = 0;
 417         WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
 418         miter->__flags = flags;
 419 }
 420 EXPORT_SYMBOL(sg_miter_start);
 421
 422 /**
 423  * sg_miter_next - proceed mapping iterator to the next mapping
 424  * @miter: sg mapping iter to proceed
 425  *
 426  * Description:
 427  *   Proceeds @miter to the next mapping.  @miter should have been started
 428  *   using sg_miter_start().  On successful return, @miter->page,
 429  *   @miter->addr and @miter->length point to the current mapping.
 430  *
 431  * Context:
 432  *   Preemption disabled if SG_MITER_ATOMIC.  Preemption must stay disabled
 433  *   till @miter is stopped.  May sleep if !SG_MITER_ATOMIC.
 434  *
 435  * Returns:
 436  *   true if @miter contains the next mapping.  false if end of sg
 437  *   list is reached.
 438  */
 439 bool sg_miter_next(struct sg_mapping_iter *miter)
 440 {
 441         unsigned int off, len;
 442
 443         /* check for end and drop resources from the last iteration */
 444         if (!miter->__nents)
 445                 return false;
 446
 447         sg_miter_stop(miter);
 448
 449         /* get to the next sg if necessary.  __offset is adjusted by stop */
 450         while (miter->__offset == miter->__sg->length) {
 451                 if (--miter->__nents) {
 452                         miter->__sg = sg_next(miter->__sg);
 453                         miter->__offset = 0;
 454                 } else
 455                         return false;
 456         }
 457
 458         /* map the next page */
 459         off = miter->__sg->offset + miter->__offset;
 460         len = miter->__sg->length - miter->__offset;
 461
 462         miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
 463         off &= ~PAGE_MASK;
 464         miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
 465         miter->consumed = miter->length;
 466
 467         if (miter->__flags & SG_MITER_ATOMIC)
 468                 miter->addr = kmap_atomic(miter->page) + off;
 469         else
 470                 miter->addr = kmap(miter->page) + off;
 471
 472         return true;
 473 }
 474 EXPORT_SYMBOL(sg_miter_next);
 475
 476 /**
 477  * sg_miter_stop - stop mapping iteration
 478  * @miter: sg mapping iter to be stopped
 479  *
 480  * Description:
 481  *   Stops mapping iterator @miter.  @miter should have been started
 482  *   started using sg_miter_start().  A stopped iteration can be
 483  *   resumed by calling sg_miter_next() on it.  This is useful when
 484  *   resources (kmap) need to be released during iteration.
 485  *
 486  * Context:
 487  *   Preemption disabled if the SG_MITER_ATOMIC is set.  Don't care
 488  *   otherwise.
 489  */
 490 void sg_miter_stop(struct sg_mapping_iter *miter)
 491 {
 492         WARN_ON(miter->consumed > miter->length);
 493
 494         /* drop resources from the last iteration */
 495         if (miter->addr) {
 496                 miter->__offset += miter->consumed;
 497
 498                 if (miter->__flags & SG_MITER_TO_SG)
 499                         flush_kernel_dcache_page(miter->page);
 500
 501                 if (miter->__flags & SG_MITER_ATOMIC) {
 502                         WARN_ON_ONCE(preemptible());
 503                         kunmap_atomic(miter->addr);
 504                 } else
 505                         kunmap(miter->page);
 506
 507                 miter->page = NULL;
 508                 miter->addr = NULL;
 509                 miter->length = 0;
 510                 miter->consumed = 0;
 511         }
 512 }
 513 EXPORT_SYMBOL(sg_miter_stop);
 514
 515 /**
 516  * sg_copy_buffer - Copy data between a linear buffer and an SG list
 517  * @sgl:                 The SG list
 518  * @nents:               Number of SG entries
 519  * @buf:                 Where to copy from
 520  * @buflen:              The number of bytes to copy
 521  * @to_buffer:           transfer direction (non zero == from an sg list to a
 522  *                       buffer, 0 == from a buffer to an sg list
 523  *
 524  * Returns the number of copied bytes.
 525  *
 526  **/
 527 static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 528                              void *buf, size_t buflen, int to_buffer)
 529 {
 530         unsigned int offset = 0;
 531         struct sg_mapping_iter miter;
 532         unsigned long flags;
 533         unsigned int sg_flags = SG_MITER_ATOMIC;
 534
 535         if (to_buffer)
 536                 sg_flags |= SG_MITER_FROM_SG;
 537         else
 538                 sg_flags |= SG_MITER_TO_SG;
 539
 540         sg_miter_start(&miter, sgl, nents, sg_flags);
 541
 542         local_irq_save(flags);
 543
 544         while (sg_miter_next(&miter) && offset < buflen) {
 545                 unsigned int len;
 546
 547                 len = min(miter.length, buflen - offset);
 548
 549                 if (to_buffer)
 550                         memcpy(buf + offset, miter.addr, len);
 551                 else
 552                         memcpy(miter.addr, buf + offset, len);
 553
 554                 offset += len;
 555         }
 556
 557         sg_miter_stop(&miter);
 558
 559         local_irq_restore(flags);
 560         return offset;
 561 }
 562
 563 /**
 564  * sg_copy_from_buffer - Copy from a linear buffer to an SG list
 565  * @sgl:                 The SG list
 566  * @nents:               Number of SG entries
 567  * @buf:                 Where to copy from
 568  * @buflen:              The number of bytes to copy
 569  *
 570  * Returns the number of copied bytes.
 571  *
 572  **/
 573 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 574                            void *buf, size_t buflen)
 575 {
 576         return sg_copy_buffer(sgl, nents, buf, buflen, 0);
 577 }
 578 EXPORT_SYMBOL(sg_copy_from_buffer);
 579
 580 /**
 581  * sg_copy_to_buffer - Copy from an SG list to a linear buffer
 582  * @sgl:                 The SG list
 583  * @nents:               Number of SG entries
 584  * @buf:                 Where to copy to
 585  * @buflen:              The number of bytes to copy
 586  *
 587  * Returns the number of copied bytes.
 588  *
 589  **/
 590 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 591                          void *buf, size_t buflen)
 592 {
 593         return sg_copy_buffer(sgl, nents, buf, buflen, 1);
 594 }
 595 EXPORT_SYMBOL(sg_copy_to_buffer);