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