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/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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