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/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  **/
  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  **/
  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  **/
  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  **/
 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  */
 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
 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  **/
 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  **/
 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  **/
 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  **/
 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  */
 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  */
 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         while (miter->__offset == miter->__sg->length) {
 351                 if (--miter->__nents) {
 352                         miter->__sg = sg_next(miter->__sg);
 353                         miter->__offset = 0;
 354                 } else
 355                         return false;
 356         }
 357
 358         /* map the next page */
 359         off = miter->__sg->offset + miter->__offset;
 360         len = miter->__sg->length - miter->__offset;
 361
 362         miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
 363         off &= ~PAGE_MASK;
 364         miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
 365         miter->consumed = miter->length;
 366
 367         if (miter->__flags & SG_MITER_ATOMIC)
 368                 miter->addr = kmap_atomic(miter->page, KM_BIO_SRC_IRQ) + off;
 369         else
 370                 miter->addr = kmap(miter->page) + off;
 371
 372         return true;
 373 }
 374 EXPORT_SYMBOL(sg_miter_next);
 375
 376 /**
 377  * sg_miter_stop - stop mapping iteration
 378  * @miter: sg mapping iter to be stopped
 379  *
 380  * Description:
 381  *   Stops mapping iterator @miter.  @miter should have been started
 382  *   started using sg_miter_start().  A stopped iteration can be
 383  *   resumed by calling sg_miter_next() on it.  This is useful when
 384  *   resources (kmap) need to be released during iteration.
 385  *
 386  * Context:
 387  *   IRQ disabled if the SG_MITER_ATOMIC is set.  Don't care otherwise.
 388  */
 389 void sg_miter_stop(struct sg_mapping_iter *miter)
 390 {
 391         WARN_ON(miter->consumed > miter->length);
 392
 393         /* drop resources from the last iteration */
 394         if (miter->addr) {
 395                 miter->__offset += miter->consumed;
 396
 397                 if (miter->__flags & SG_MITER_ATOMIC) {
 398                         WARN_ON(!irqs_disabled());
 399                         kunmap_atomic(miter->addr, KM_BIO_SRC_IRQ);
 400                 } else
 401                         kunmap(miter->page);
 402
 403                 miter->page = NULL;
 404                 miter->addr = NULL;
 405                 miter->length = 0;
 406                 miter->consumed = 0;
 407         }
 408 }
 409 EXPORT_SYMBOL(sg_miter_stop);
 410
 411 /**
 412  * sg_copy_buffer - Copy data between a linear buffer and an SG list
 413  * @sgl:                 The SG list
 414  * @nents:               Number of SG entries
 415  * @buf:                 Where to copy from
 416  * @buflen:              The number of bytes to copy
 417  * @to_buffer:           transfer direction (non zero == from an sg list to a
 418  *                       buffer, 0 == from a buffer to an sg list
 419  *
 420  * Returns the number of copied bytes.
 421  *
 422  **/
 423 static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 424                              void *buf, size_t buflen, int to_buffer)
 425 {
 426         unsigned int offset = 0;
 427         struct sg_mapping_iter miter;
 428         unsigned long flags;
 429
 430         sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC);
 431
 432         local_irq_save(flags);
 433
 434         while (sg_miter_next(&miter) && offset < buflen) {
 435                 unsigned int len;
 436
 437                 len = min(miter.length, buflen - offset);
 438
 439                 if (to_buffer)
 440                         memcpy(buf + offset, miter.addr, len);
 441                 else {
 442                         memcpy(miter.addr, buf + offset, len);
 443                         flush_kernel_dcache_page(miter.page);
 444                 }
 445
 446                 offset += len;
 447         }
 448
 449         sg_miter_stop(&miter);
 450
 451         local_irq_restore(flags);
 452         return offset;
 453 }
 454
 455 /**
 456  * sg_copy_from_buffer - Copy from a linear buffer to an SG list
 457  * @sgl:                 The SG list
 458  * @nents:               Number of SG entries
 459  * @buf:                 Where to copy from
 460  * @buflen:              The number of bytes to copy
 461  *
 462  * Returns the number of copied bytes.
 463  *
 464  **/
 465 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 466                            void *buf, size_t buflen)
 467 {
 468         return sg_copy_buffer(sgl, nents, buf, buflen, 0);
 469 }
 470 EXPORT_SYMBOL(sg_copy_from_buffer);
 471
 472 /**
 473  * sg_copy_to_buffer - Copy from an SG list to a linear buffer
 474  * @sgl:                 The SG list
 475  * @nents:               Number of SG entries
 476  * @buf:                 Where to copy to
 477  * @buflen:              The number of bytes to copy
 478  *
 479  * Returns the number of copied bytes.
 480  *
 481  **/
 482 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 483                          void *buf, size_t buflen)
 484 {
 485         return sg_copy_buffer(sgl, nents, buf, buflen, 1);
 486 }
 487 EXPORT_SYMBOL(sg_copy_to_buffer);