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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
  *
  * Scatterlist handling helpers.
  */
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/scatterlist.h>
 #include <linux/highmem.h>
 #include <linux/kmemleak.h>
 
 /**
  * sg_next - return the next scatterlist entry in a list
  * @sg:     The current sg entry
  *
  * Description:
  *   Usually the next entry will be @sg@ + 1, but if this sg element is part
  *   of a chained scatterlist, it could jump to the start of a new
  *   scatterlist array.
  *
  **/
 struct scatterlist *sg_next(struct scatterlist *sg)
 {
     if (sg_is_last(sg))
         return NULL;
 
     sg++;
     if (unlikely(sg_is_chain(sg)))
         sg = sg_chain_ptr(sg);
 
     return sg;
 }
 EXPORT_SYMBOL(sg_next);
 
 /**
  * sg_nents - return total count of entries in scatterlist
  * @sg:     The scatterlist
  *
  * Description:
  * Allows to know how many entries are in sg, taking into account
  * chaining as well
  *
  **/
 int sg_nents(struct scatterlist *sg)
 {
     int nents;
     for (nents = 0; sg; sg = sg_next(sg))
         nents++;
     return nents;
 }
 EXPORT_SYMBOL(sg_nents);
 
 /**
  * sg_nents_for_len - return total count of entries in scatterlist
  *                    needed to satisfy the supplied length
  * @sg:     The scatterlist
  * @len:    The total required length
  *
  * Description:
  * Determines the number of entries in sg that are required to meet
  * the supplied length, taking into account chaining as well
  *
  * Returns:
  *   the number of sg entries needed, negative error on failure
  *
  **/
 int sg_nents_for_len(struct scatterlist *sg, u64 len)
 {
     int nents;
     u64 total;
 
     if (!len)
         return 0;
 
     for (nents = 0, total = 0; sg; sg = sg_next(sg)) {
         nents++;
         total += sg->length;
         if (total >= len)
             return nents;
     }
 
     return -EINVAL;
 }
 EXPORT_SYMBOL(sg_nents_for_len);
 
 /**
  * sg_last - return the last scatterlist entry in a list
  * @sgl:    First entry in the scatterlist
  * @nents:  Number of entries in the scatterlist
  *
  * Description:
  *   Should only be used casually, it (currently) scans the entire list
  *   to get the last entry.
  *
  *   Note that the @sgl@ pointer passed in need not be the first one,
  *   the important bit is that @nents@ denotes the number of entries that
  *   exist from @sgl@.
  *
  **/
 struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
 {
     struct scatterlist *sg, *ret = NULL;
     unsigned int i;
 
     for_each_sg(sgl, sg, nents, i)
         ret = sg;
 
     BUG_ON(!sg_is_last(ret));
     return ret;
 }
 EXPORT_SYMBOL(sg_last);
 
 /**
  * sg_init_table - Initialize SG table
  * @sgl:       The SG table
  * @nents:     Number of entries in table
  *
  * Notes:
  *   If this is part of a chained sg table, sg_mark_end() should be
  *   used only on the last table part.
  *
  **/
 void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 {
     memset(sgl, 0, sizeof(*sgl) * nents);
     sg_init_marker(sgl, nents);
 }
 EXPORT_SYMBOL(sg_init_table);
 
 /**
  * sg_init_one - Initialize a single entry sg list
  * @sg:      SG entry
  * @buf:     Virtual address for IO
  * @buflen:  IO length
  *
  **/
 void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
 {
     sg_init_table(sg, 1);
     sg_set_buf(sg, buf, buflen);
 }
 EXPORT_SYMBOL(sg_init_one);
 
 /*
  * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
  * helpers.
  */
 static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
 {
     if (nents == SG_MAX_SINGLE_ALLOC) {
         /*
          * Kmemleak doesn't track page allocations as they are not
          * commonly used (in a raw form) for kernel data structures.
          * As we chain together a list of pages and then a normal
          * kmalloc (tracked by kmemleak), in order to for that last
          * allocation not to become decoupled (and thus a
          * false-positive) we need to inform kmemleak of all the
          * intermediate allocations.
          */
         void *ptr = (void *) __get_free_page(gfp_mask);
         kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask);
         return ptr;
     } else
         return kmalloc_array(nents, sizeof(struct scatterlist),
                      gfp_mask);
 }
 
 static void sg_kfree(struct scatterlist *sg, unsigned int nents)
 {
     if (nents == SG_MAX_SINGLE_ALLOC) {
         kmemleak_free(sg);
         free_page((unsigned long) sg);
     } else
         kfree(sg);
 }
 
 /**
  * __sg_free_table - Free a previously mapped sg table
  * @table:  The sg table header to use
  * @max_ents:   The maximum number of entries per single scatterlist
  * @nents_first_chunk: Number of entries int the (preallocated) first
  *  scatterlist chunk, 0 means no such preallocated first chunk
  * @free_fn:    Free function
  * @num_ents:   Number of entries in the table
  *
  *  Description:
  *    Free an sg table previously allocated and setup with
  *    __sg_alloc_table().  The @max_ents value must be identical to
  *    that previously used with __sg_alloc_table().
  *
  **/
 void __sg_free_table(struct sg_table *table, unsigned int max_ents,
              unsigned int nents_first_chunk, sg_free_fn *free_fn,
              unsigned int num_ents)
 {
     struct scatterlist *sgl, *next;
     unsigned curr_max_ents = nents_first_chunk ?: max_ents;
 
     if (unlikely(!table->sgl))
         return;
 
     sgl = table->sgl;
     while (num_ents) {
         unsigned int alloc_size = num_ents;
         unsigned int sg_size;
 
         /*
          * If we have more than max_ents segments left,
          * then assign 'next' to the sg table after the current one.
          * sg_size is then one less than alloc size, since the last
          * element is the chain pointer.
          */
         if (alloc_size > curr_max_ents) {
             next = sg_chain_ptr(&sgl[curr_max_ents - 1]);
             alloc_size = curr_max_ents;
             sg_size = alloc_size - 1;
         } else {
             sg_size = alloc_size;
             next = NULL;
         }
 
         num_ents -= sg_size;
         if (nents_first_chunk)
             nents_first_chunk = 0;
         else
             free_fn(sgl, alloc_size);
         sgl = next;
         curr_max_ents = max_ents;
     }
 
     table->sgl = NULL;
 }
 EXPORT_SYMBOL(__sg_free_table);
 
 /**
  * sg_free_append_table - Free a previously allocated append sg table.
  * @table:   The mapped sg append table header
  *
  **/
 void sg_free_append_table(struct sg_append_table *table)
 {
     __sg_free_table(&table->sgt, SG_MAX_SINGLE_ALLOC, 0, sg_kfree,
             table->total_nents);
 }
 EXPORT_SYMBOL(sg_free_append_table);
 
 
 /**
  * sg_free_table - Free a previously allocated sg table
  * @table:  The mapped sg table header
  *
  **/
 void sg_free_table(struct sg_table *table)
 {
     __sg_free_table(table, SG_MAX_SINGLE_ALLOC, 0, sg_kfree,
             table->orig_nents);
 }
 EXPORT_SYMBOL(sg_free_table);
 
 /**
  * __sg_alloc_table - Allocate and initialize an sg table with given allocator
  * @table:  The sg table header to use
  * @nents:  Number of entries in sg list
  * @max_ents:   The maximum number of entries the allocator returns per call
  * @nents_first_chunk: Number of entries int the (preallocated) first
  *  scatterlist chunk, 0 means no such preallocated chunk provided by user
  * @gfp_mask:   GFP allocation mask
  * @alloc_fn:   Allocator to use
  *
  * Description:
  *   This function returns a @table @nents long. The allocator is
  *   defined to return scatterlist chunks of maximum size @max_ents.
  *   Thus if @nents is bigger than @max_ents, the scatterlists will be
  *   chained in units of @max_ents.
  *
  * Notes:
  *   If this function returns non-0 (eg failure), the caller must call
  *   __sg_free_table() to cleanup any leftover allocations.
  *
  **/
 int __sg_alloc_table(struct sg_table *table, unsigned int nents,
              unsigned int max_ents, struct scatterlist *first_chunk,
              unsigned int nents_first_chunk, gfp_t gfp_mask,
              sg_alloc_fn *alloc_fn)
 {
     struct scatterlist *sg, *prv;
     unsigned int left;
     unsigned curr_max_ents = nents_first_chunk ?: max_ents;
     unsigned prv_max_ents;
 
     memset(table, 0, sizeof(*table));
 
     if (nents == 0)
         return -EINVAL;
 #ifdef CONFIG_ARCH_NO_SG_CHAIN
     if (WARN_ON_ONCE(nents > max_ents))
         return -EINVAL;
 #endif
 
     left = nents;
     prv = NULL;
     do {
         unsigned int sg_size, alloc_size = left;
 
         if (alloc_size > curr_max_ents) {
             alloc_size = curr_max_ents;
             sg_size = alloc_size - 1;
         } else
             sg_size = alloc_size;
 
         left -= sg_size;
 
         if (first_chunk) {
             sg = first_chunk;
             first_chunk = NULL;
         } else {
             sg = alloc_fn(alloc_size, gfp_mask);
         }
         if (unlikely(!sg)) {
             /*
              * Adjust entry count to reflect that the last
              * entry of the previous table won't be used for
              * linkage.  Without this, sg_kfree() may get
              * confused.
              */
             if (prv)
                 table->nents = ++table->orig_nents;
 
             return -ENOMEM;
         }
 
         sg_init_table(sg, alloc_size);
         table->nents = table->orig_nents += sg_size;
 
         /*
          * If this is the first mapping, assign the sg table header.
          * If this is not the first mapping, chain previous part.
          */
         if (prv)
             sg_chain(prv, prv_max_ents, sg);
         else
             table->sgl = sg;
 
         /*
          * If no more entries after this one, mark the end
          */
         if (!left)
             sg_mark_end(&sg[sg_size - 1]);
 
         prv = sg;
         prv_max_ents = curr_max_ents;
         curr_max_ents = max_ents;
     } while (left);
 
     return 0;
 }
 EXPORT_SYMBOL(__sg_alloc_table);
 
 /**
  * sg_alloc_table - Allocate and initialize an sg table
  * @table:  The sg table header to use
  * @nents:  Number of entries in sg list
  * @gfp_mask:   GFP allocation mask
  *
  *  Description:
  *    Allocate and initialize an sg table. If @nents@ is larger than
  *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
  *
  **/
 int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
 {
     int ret;
 
     ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
                    NULL, 0, gfp_mask, sg_kmalloc);
     if (unlikely(ret))
         sg_free_table(table);
     return ret;
 }
 EXPORT_SYMBOL(sg_alloc_table);
 
 static struct scatterlist *get_next_sg(struct sg_append_table *table,
                        struct scatterlist *cur,
                        unsigned long needed_sges,
                        gfp_t gfp_mask)
 {
     struct scatterlist *new_sg, *next_sg;
     unsigned int alloc_size;
 
     if (cur) {
         next_sg = sg_next(cur);
         /* Check if last entry should be keeped for chainning */
         if (!sg_is_last(next_sg) || needed_sges == 1)
             return next_sg;
     }
 
     alloc_size = min_t(unsigned long, needed_sges, SG_MAX_SINGLE_ALLOC);
     new_sg = sg_kmalloc(alloc_size, gfp_mask);
     if (!new_sg)
         return ERR_PTR(-ENOMEM);
     sg_init_table(new_sg, alloc_size);
     if (cur) {
         table->total_nents += alloc_size - 1;
         __sg_chain(next_sg, new_sg);
     } else {
         table->sgt.sgl = new_sg;
         table->total_nents = alloc_size;
     }
     return new_sg;
 }
 
 /**
  * sg_alloc_append_table_from_pages - Allocate and initialize an append sg
  *                                    table from an array of pages
  * @sgt_append:  The sg append table to use
  * @pages:       Pointer to an array of page pointers
  * @n_pages:     Number of pages in the pages array
  * @offset:      Offset from start of the first page to the start of a buffer
  * @size:        Number of valid bytes in the buffer (after offset)
  * @max_segment: Maximum size of a scatterlist element in bytes
  * @left_pages:  Left pages caller have to set after this call
  * @gfp_mask:    GFP allocation mask
  *
  * Description:
  *    In the first call it allocate and initialize an sg table from a list of
  *    pages, else reuse the scatterlist from sgt_append. Contiguous ranges of
  *    the pages are squashed into a single scatterlist entry up to the maximum
  *    size specified in @max_segment.  A user may provide an offset at a start
  *    and a size of valid data in a buffer specified by the page array. The
  *    returned sg table is released by sg_free_append_table
  *
  * Returns:
  *   0 on success, negative error on failure
  *
  * Notes:
  *   If this function returns non-0 (eg failure), the caller must call
  *   sg_free_append_table() to cleanup any leftover allocations.
  *
  *   In the fist call, sgt_append must by initialized.
  */
 int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
         struct page **pages, unsigned int n_pages, unsigned int offset,
         unsigned long size, unsigned int max_segment,
         unsigned int left_pages, gfp_t gfp_mask)
 {
     unsigned int chunks, cur_page, seg_len, i, prv_len = 0;
     unsigned int added_nents = 0;
     struct scatterlist *s = sgt_append->prv;
 
     /*
      * The algorithm below requires max_segment to be aligned to PAGE_SIZE
      * otherwise it can overshoot.
      */
     max_segment = ALIGN_DOWN(max_segment, PAGE_SIZE);
     if (WARN_ON(max_segment < PAGE_SIZE))
         return -EINVAL;
 
     if (IS_ENABLED(CONFIG_ARCH_NO_SG_CHAIN) && sgt_append->prv)
         return -EOPNOTSUPP;
 
     if (sgt_append->prv) {
         unsigned long paddr =
             (page_to_pfn(sg_page(sgt_append->prv)) * PAGE_SIZE +
              sgt_append->prv->offset + sgt_append->prv->length) /
             PAGE_SIZE;
 
         if (WARN_ON(offset))
             return -EINVAL;
 
         /* Merge contiguous pages into the last SG */
         prv_len = sgt_append->prv->length;
         while (n_pages && page_to_pfn(pages[0]) == paddr) {
             if (sgt_append->prv->length + PAGE_SIZE > max_segment)
                 break;
             sgt_append->prv->length += PAGE_SIZE;
             paddr++;
             pages++;
             n_pages--;
         }
         if (!n_pages)
             goto out;
     }
 
     /* compute number of contiguous chunks */
     chunks = 1;
     seg_len = 0;
     for (i = 1; i < n_pages; i++) {
         seg_len += PAGE_SIZE;
         if (seg_len >= max_segment ||
             page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) {
             chunks++;
             seg_len = 0;
         }
     }
 
     /* merging chunks and putting them into the scatterlist */
     cur_page = 0;
     for (i = 0; i < chunks; i++) {
         unsigned int j, chunk_size;
 
         /* look for the end of the current chunk */
         seg_len = 0;
         for (j = cur_page + 1; j < n_pages; j++) {
             seg_len += PAGE_SIZE;
             if (seg_len >= max_segment ||
                 page_to_pfn(pages[j]) !=
                 page_to_pfn(pages[j - 1]) + 1)
                 break;
         }
 
         /* Pass how many chunks might be left */
         s = get_next_sg(sgt_append, s, chunks - i + left_pages,
                 gfp_mask);
         if (IS_ERR(s)) {
             /*
              * Adjust entry length to be as before function was
              * called.
              */
             if (sgt_append->prv)
                 sgt_append->prv->length = prv_len;
             return PTR_ERR(s);
         }
         chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
         sg_set_page(s, pages[cur_page],
                 min_t(unsigned long, size, chunk_size), offset);
         added_nents++;
         size -= chunk_size;
         offset = 0;
         cur_page = j;
     }
     sgt_append->sgt.nents += added_nents;
     sgt_append->sgt.orig_nents = sgt_append->sgt.nents;
     sgt_append->prv = s;
 out:
     if (!left_pages)
         sg_mark_end(s);
     return 0;
 }
 EXPORT_SYMBOL(sg_alloc_append_table_from_pages);
 
 /**
  * sg_alloc_table_from_pages_segment - Allocate and initialize an sg table from
  *                                     an array of pages and given maximum
  *                                     segment.
  * @sgt:     The sg table header to use
  * @pages:   Pointer to an array of page pointers
  * @n_pages:     Number of pages in the pages array
  * @offset:      Offset from start of the first page to the start of a buffer
  * @size:        Number of valid bytes in the buffer (after offset)
  * @max_segment: Maximum size of a scatterlist element in bytes
  * @gfp_mask:    GFP allocation mask
  *
  *  Description:
  *    Allocate and initialize an sg table from a list of pages. Contiguous
  *    ranges of the pages are squashed into a single scatterlist node up to the
  *    maximum size specified in @max_segment. A user may provide an offset at a
  *    start and a size of valid data in a buffer specified by the page array.
  *
  *    The returned sg table is released by sg_free_table.
  *
  *  Returns:
  *   0 on success, negative error on failure
  */
 int sg_alloc_table_from_pages_segment(struct sg_table *sgt, struct page **pages,
                 unsigned int n_pages, unsigned int offset,
                 unsigned long size, unsigned int max_segment,
                 gfp_t gfp_mask)
 {
     struct sg_append_table append = {};
     int err;
 
     err = sg_alloc_append_table_from_pages(&append, pages, n_pages, offset,
                            size, max_segment, 0, gfp_mask);
     if (err) {
         sg_free_append_table(&append);
         return err;
     }
     memcpy(sgt, &append.sgt, sizeof(*sgt));
     WARN_ON(append.total_nents != sgt->orig_nents);
     return 0;
 }
 EXPORT_SYMBOL(sg_alloc_table_from_pages_segment);
 
 #ifdef CONFIG_SGL_ALLOC
 
 /**
  * sgl_alloc_order - allocate a scatterlist and its pages
  * @length: Length in bytes of the scatterlist. Must be at least one
  * @order: Second argument for alloc_pages()
  * @chainable: Whether or not to allocate an extra element in the scatterlist
  *  for scatterlist chaining purposes
  * @gfp: Memory allocation flags
  * @nent_p: [out] Number of entries in the scatterlist that have pages
  *
  * Returns: A pointer to an initialized scatterlist or %NULL upon failure.
  */
 struct scatterlist *sgl_alloc_order(unsigned long long length,
                     unsigned int order, bool chainable,
                     gfp_t gfp, unsigned int *nent_p)
 {
     struct scatterlist *sgl, *sg;
     struct page *page;
     unsigned int nent, nalloc;
     u32 elem_len;
 
     nent = round_up(length, PAGE_SIZE << order) >> (PAGE_SHIFT + order);
     /* Check for integer overflow */
     if (length > (nent << (PAGE_SHIFT + order)))
         return NULL;
     nalloc = nent;
     if (chainable) {
         /* Check for integer overflow */
         if (nalloc + 1 < nalloc)
             return NULL;
         nalloc++;
     }
     sgl = kmalloc_array(nalloc, sizeof(struct scatterlist),
                 gfp & ~GFP_DMA);
     if (!sgl)
         return NULL;
 
     sg_init_table(sgl, nalloc);
     sg = sgl;
     while (length) {
         elem_len = min_t(u64, length, PAGE_SIZE << order);
         page = alloc_pages(gfp, order);
         if (!page) {
             sgl_free_order(sgl, order);
             return NULL;
         }
 
         sg_set_page(sg, page, elem_len, 0);
         length -= elem_len;
         sg = sg_next(sg);
     }
     WARN_ONCE(length, "length = %lld\n", length);
     if (nent_p)
         *nent_p = nent;
     return sgl;
 }
 EXPORT_SYMBOL(sgl_alloc_order);
 
 /**
  * sgl_alloc - allocate a scatterlist and its pages
  * @length: Length in bytes of the scatterlist
  * @gfp: Memory allocation flags
  * @nent_p: [out] Number of entries in the scatterlist
  *
  * Returns: A pointer to an initialized scatterlist or %NULL upon failure.
  */
 struct scatterlist *sgl_alloc(unsigned long long length, gfp_t gfp,
                   unsigned int *nent_p)
 {
     return sgl_alloc_order(length, 0, false, gfp, nent_p);
 }
 EXPORT_SYMBOL(sgl_alloc);
 
 /**
  * sgl_free_n_order - free a scatterlist and its pages
  * @sgl: Scatterlist with one or more elements
  * @nents: Maximum number of elements to free
  * @order: Second argument for __free_pages()
  *
  * Notes:
  * - If several scatterlists have been chained and each chain element is
  *   freed separately then it's essential to set nents correctly to avoid that a
  *   page would get freed twice.
  * - All pages in a chained scatterlist can be freed at once by setting @nents
  *   to a high number.
  */
 void sgl_free_n_order(struct scatterlist *sgl, int nents, int order)
 {
     struct scatterlist *sg;
     struct page *page;
     int i;
 
     for_each_sg(sgl, sg, nents, i) {
         if (!sg)
             break;
         page = sg_page(sg);
         if (page)
             __free_pages(page, order);
     }
     kfree(sgl);
 }
 EXPORT_SYMBOL(sgl_free_n_order);
 
 /**
  * sgl_free_order - free a scatterlist and its pages
  * @sgl: Scatterlist with one or more elements
  * @order: Second argument for __free_pages()
  */
 void sgl_free_order(struct scatterlist *sgl, int order)
 {
     sgl_free_n_order(sgl, INT_MAX, order);
 }
 EXPORT_SYMBOL(sgl_free_order);
 
 /**
  * sgl_free - free a scatterlist and its pages
  * @sgl: Scatterlist with one or more elements
  */
 void sgl_free(struct scatterlist *sgl)
 {
     sgl_free_order(sgl, 0);
 }
 EXPORT_SYMBOL(sgl_free);
 
 #endif /* CONFIG_SGL_ALLOC */
 
 void __sg_page_iter_start(struct sg_page_iter *piter,
               struct scatterlist *sglist, unsigned int nents,
               unsigned long pgoffset)
 {
     piter->__pg_advance = 0;
     piter->__nents = nents;
 
     piter->sg = sglist;
     piter->sg_pgoffset = pgoffset;
 }
 EXPORT_SYMBOL(__sg_page_iter_start);
 
 static int sg_page_count(struct scatterlist *sg)
 {
     return PAGE_ALIGN(sg->offset + sg->length) >> PAGE_SHIFT;
 }
 
 bool __sg_page_iter_next(struct sg_page_iter *piter)
 {
     if (!piter->__nents || !piter->sg)
         return false;
 
     piter->sg_pgoffset += piter->__pg_advance;
     piter->__pg_advance = 1;
 
     while (piter->sg_pgoffset >= sg_page_count(piter->sg)) {
         piter->sg_pgoffset -= sg_page_count(piter->sg);
         piter->sg = sg_next(piter->sg);
         if (!--piter->__nents || !piter->sg)
             return false;
     }
 
     return true;
 }
 EXPORT_SYMBOL(__sg_page_iter_next);
 
 static int sg_dma_page_count(struct scatterlist *sg)
 {
     return PAGE_ALIGN(sg->offset + sg_dma_len(sg)) >> PAGE_SHIFT;
 }
 
 bool __sg_page_iter_dma_next(struct sg_dma_page_iter *dma_iter)
 {
     struct sg_page_iter *piter = &dma_iter->base;
 
     if (!piter->__nents || !piter->sg)
         return false;
 
     piter->sg_pgoffset += piter->__pg_advance;
     piter->__pg_advance = 1;
 
     while (piter->sg_pgoffset >= sg_dma_page_count(piter->sg)) {
         piter->sg_pgoffset -= sg_dma_page_count(piter->sg);
         piter->sg = sg_next(piter->sg);
         if (!--piter->__nents || !piter->sg)
             return false;
     }
 
     return true;
 }
 EXPORT_SYMBOL(__sg_page_iter_dma_next);
 
 /**
  * sg_miter_start - start mapping iteration over a sg list
  * @miter: sg mapping iter to be started
  * @sgl: sg list to iterate over
  * @nents: number of sg entries
  *
  * Description:
  *   Starts mapping iterator @miter.
  *
  * Context:
  *   Don't care.
  */
 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
             unsigned int nents, unsigned int flags)
 {
     memset(miter, 0, sizeof(struct sg_mapping_iter));
 
     __sg_page_iter_start(&miter->piter, sgl, nents, 0);
     WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
     miter->__flags = flags;
 }
 EXPORT_SYMBOL(sg_miter_start);
 
 static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
 {
     if (!miter->__remaining) {
         struct scatterlist *sg;
 
         if (!__sg_page_iter_next(&miter->piter))
             return false;
 
         sg = miter->piter.sg;
 
         miter->__offset = miter->piter.sg_pgoffset ? 0 : sg->offset;
         miter->piter.sg_pgoffset += miter->__offset >> PAGE_SHIFT;
         miter->__offset &= PAGE_SIZE - 1;
         miter->__remaining = sg->offset + sg->length -
                      (miter->piter.sg_pgoffset << PAGE_SHIFT) -
                      miter->__offset;
         miter->__remaining = min_t(unsigned long, miter->__remaining,
                        PAGE_SIZE - miter->__offset);
     }
 
     return true;
 }
 
 /**
  * sg_miter_skip - reposition mapping iterator
  * @miter: sg mapping iter to be skipped
  * @offset: number of bytes to plus the current location
  *
  * Description:
  *   Sets the offset of @miter to its current location plus @offset bytes.
  *   If mapping iterator @miter has been proceeded by sg_miter_next(), this
  *   stops @miter.
  *
  * Context:
  *   Don't care.
  *
  * Returns:
  *   true if @miter contains the valid mapping.  false if end of sg
  *   list is reached.
  */
 bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset)
 {
     sg_miter_stop(miter);
 
     while (offset) {
         off_t consumed;
 
         if (!sg_miter_get_next_page(miter))
             return false;
 
         consumed = min_t(off_t, offset, miter->__remaining);
         miter->__offset += consumed;
         miter->__remaining -= consumed;
         offset -= consumed;
     }
 
     return true;
 }
 EXPORT_SYMBOL(sg_miter_skip);
 
 /**
  * sg_miter_next - proceed mapping iterator to the next mapping
  * @miter: sg mapping iter to proceed
  *
  * Description:
  *   Proceeds @miter to the next mapping.  @miter should have been started
  *   using sg_miter_start().  On successful return, @miter->page,
  *   @miter->addr and @miter->length point to the current mapping.
  *
  * Context:
  *   May sleep if !SG_MITER_ATOMIC.
  *
  * Returns:
  *   true if @miter contains the next mapping.  false if end of sg
  *   list is reached.
  */
 bool sg_miter_next(struct sg_mapping_iter *miter)
 {
     sg_miter_stop(miter);
 
     /*
      * Get to the next page if necessary.
      * __remaining, __offset is adjusted by sg_miter_stop
      */
     if (!sg_miter_get_next_page(miter))
         return false;
 
     miter->page = sg_page_iter_page(&miter->piter);
     miter->consumed = miter->length = miter->__remaining;
 
     if (miter->__flags & SG_MITER_ATOMIC)
         miter->addr = kmap_atomic(miter->page) + miter->__offset;
     else
         miter->addr = kmap(miter->page) + miter->__offset;
 
     return true;
 }
 EXPORT_SYMBOL(sg_miter_next);
 
 /**
  * sg_miter_stop - stop mapping iteration
  * @miter: sg mapping iter to be stopped
  *
  * Description:
  *   Stops mapping iterator @miter.  @miter should have been started
  *   using sg_miter_start().  A stopped iteration can be resumed by
  *   calling sg_miter_next() on it.  This is useful when resources (kmap)
  *   need to be released during iteration.
  *
  * Context:
  *   Don't care otherwise.
  */
 void sg_miter_stop(struct sg_mapping_iter *miter)
 {
     WARN_ON(miter->consumed > miter->length);
 
     /* drop resources from the last iteration */
     if (miter->addr) {
         miter->__offset += miter->consumed;
         miter->__remaining -= miter->consumed;
 
         if (miter->__flags & SG_MITER_TO_SG)
             flush_dcache_page(miter->page);
 
         if (miter->__flags & SG_MITER_ATOMIC) {
             WARN_ON_ONCE(!pagefault_disabled());
             kunmap_atomic(miter->addr);
         } else
             kunmap(miter->page);
 
         miter->page = NULL;
         miter->addr = NULL;
         miter->length = 0;
         miter->consumed = 0;
     }
 }
 EXPORT_SYMBOL(sg_miter_stop);
 
 /**
  * sg_copy_buffer - Copy data between a linear buffer and an SG list
  * @sgl:         The SG list
  * @nents:       Number of SG entries
  * @buf:         Where to copy from
  * @buflen:      The number of bytes to copy
  * @skip:        Number of bytes to skip before copying
  * @to_buffer:       transfer direction (true == from an sg list to a
  *           buffer, false == from a buffer to an sg list)
  *
  * Returns the number of copied bytes.
  *
  **/
 size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
               size_t buflen, off_t skip, bool to_buffer)
 {
     unsigned int offset = 0;
     struct sg_mapping_iter miter;
     unsigned int sg_flags = SG_MITER_ATOMIC;
 
     if (to_buffer)
         sg_flags |= SG_MITER_FROM_SG;
     else
         sg_flags |= SG_MITER_TO_SG;
 
     sg_miter_start(&miter, sgl, nents, sg_flags);
 
     if (!sg_miter_skip(&miter, skip))
         return 0;
 
     while ((offset < buflen) && sg_miter_next(&miter)) {
         unsigned int len;
 
         len = min(miter.length, buflen - offset);
 
         if (to_buffer)
             memcpy(buf + offset, miter.addr, len);
         else
             memcpy(miter.addr, buf + offset, len);
 
         offset += len;
     }
 
     sg_miter_stop(&miter);
 
     return offset;
 }
 EXPORT_SYMBOL(sg_copy_buffer);
 
 /**
  * sg_copy_from_buffer - Copy from a linear buffer to an SG list
  * @sgl:         The SG list
  * @nents:       Number of SG entries
  * @buf:         Where to copy from
  * @buflen:      The number of bytes to copy
  *
  * Returns the number of copied bytes.
  *
  **/
 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
                const void *buf, size_t buflen)
 {
     return sg_copy_buffer(sgl, nents, (void *)buf, buflen, 0, false);
 }
 EXPORT_SYMBOL(sg_copy_from_buffer);
 
 /**
  * sg_copy_to_buffer - Copy from an SG list to a linear buffer
  * @sgl:         The SG list
  * @nents:       Number of SG entries
  * @buf:         Where to copy to
  * @buflen:      The number of bytes to copy
  *
  * Returns the number of copied bytes.
  *
  **/
 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
              void *buf, size_t buflen)
 {
     return sg_copy_buffer(sgl, nents, buf, buflen, 0, true);
 }
 EXPORT_SYMBOL(sg_copy_to_buffer);
 
 /**
  * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
  * @sgl:         The SG list
  * @nents:       Number of SG entries
  * @buf:         Where to copy from
  * @buflen:      The number of bytes to copy
  * @skip:        Number of bytes to skip before copying
  *
  * Returns the number of copied bytes.
  *
  **/
 size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
                 const void *buf, size_t buflen, off_t skip)
 {
     return sg_copy_buffer(sgl, nents, (void *)buf, buflen, skip, false);
 }
 EXPORT_SYMBOL(sg_pcopy_from_buffer);
 
 /**
  * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
  * @sgl:         The SG list
  * @nents:       Number of SG entries
  * @buf:         Where to copy to
  * @buflen:      The number of bytes to copy
  * @skip:        Number of bytes to skip before copying
  *
  * Returns the number of copied bytes.
  *
  **/
 size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
               void *buf, size_t buflen, off_t skip)
 {
     return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
 }
 EXPORT_SYMBOL(sg_pcopy_to_buffer);
 
 /**
  * sg_zero_buffer - Zero-out a part of a SG list
  * @sgl:         The SG list
  * @nents:       Number of SG entries
  * @buflen:      The number of bytes to zero out
  * @skip:        Number of bytes to skip before zeroing
  *
  * Returns the number of bytes zeroed.
  **/
 size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
                size_t buflen, off_t skip)
 {
     unsigned int offset = 0;
     struct sg_mapping_iter miter;
     unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;
 
     sg_miter_start(&miter, sgl, nents, sg_flags);
 
     if (!sg_miter_skip(&miter, skip))
         return false;
 
     while (offset < buflen && sg_miter_next(&miter)) {
         unsigned int len;
 
         len = min(miter.length, buflen - offset);
         memset(miter.addr, 0, len);
 
         offset += len;
     }
 
     sg_miter_stop(&miter);
     return offset;
 }
 EXPORT_SYMBOL(sg_zero_buffer);

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