Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 945 insertions, 0 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
new file mode 100644
index 000000000..3b859201f
--- /dev/null
+++ b/lib/scatterlist.c
@@ -0,0 +1,945 @@
+/*
+ * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
+ *
+ * Scatterlist handling helpers.
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2. See the file COPYING for more details.
+ */
+#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 acount
+ * 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 acount 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
+ * @skip_first_chunk: don't free the (preallocated) first scatterlist chunk
+ * @free_fn:	Free function
+ *
+ *  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,
+		     bool skip_first_chunk, sg_free_fn *free_fn)
+{
+	struct scatterlist *sgl, *next;
+
+	if (unlikely(!table->sgl))
+		return;
+
+	sgl = table->sgl;
+	while (table->orig_nents) {
+		unsigned int alloc_size = table->orig_nents;
+		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 > max_ents) {
+			next = sg_chain_ptr(&sgl[max_ents - 1]);
+			alloc_size = max_ents;
+			sg_size = alloc_size - 1;
+		} else {
+			sg_size = alloc_size;
+			next = NULL;
+		}
+
+		table->orig_nents -= sg_size;
+		if (skip_first_chunk)
+			skip_first_chunk = false;
+		else
+			free_fn(sgl, alloc_size);
+		sgl = next;
+	}
+
+	table->sgl = NULL;
+}
+EXPORT_SYMBOL(__sg_free_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, false, sg_kfree);
+}
+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
+ * @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,
+		     gfp_t gfp_mask, sg_alloc_fn *alloc_fn)
+{
+	struct scatterlist *sg, *prv;
+	unsigned int left;
+
+	memset(table, 0, sizeof(*table));
+
+	if (nents == 0)
+		return -EINVAL;
+#ifndef CONFIG_ARCH_HAS_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 > max_ents) {
+			alloc_size = 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, 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;
+	} 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, gfp_mask, sg_kmalloc);
+	if (unlikely(ret))
+		__sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
+
+	return ret;
+}
+EXPORT_SYMBOL(sg_alloc_table);
+
+/**
+ * __sg_alloc_table_from_pages - Allocate and initialize an sg table from
+ *			         an array of pages
+ * @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 node in bytes (page aligned)
+ * @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. An 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(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)
+{
+	unsigned int chunks, cur_page, seg_len, i;
+	int ret;
+	struct scatterlist *s;
+
+	if (WARN_ON(!max_segment || offset_in_page(max_segment)))
+		return -EINVAL;
+
+	/* 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;
+		}
+	}
+
+	ret = sg_alloc_table(sgt, chunks, gfp_mask);
+	if (unlikely(ret))
+		return ret;
+
+	/* merging chunks and putting them into the scatterlist */
+	cur_page = 0;
+	for_each_sg(sgt->sgl, s, sgt->orig_nents, 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;
+		}
+
+		chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
+		sg_set_page(s, pages[cur_page],
+			    min_t(unsigned long, size, chunk_size), offset);
+		size -= chunk_size;
+		offset = 0;
+		cur_page = j;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(__sg_alloc_table_from_pages);
+
+/**
+ * sg_alloc_table_from_pages - Allocate and initialize an sg table from
+ *			       an array of pages
+ * @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)
+ * @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. 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(struct sg_table *sgt, struct page **pages,
+			      unsigned int n_pages, unsigned int offset,
+			      unsigned long size, gfp_t gfp_mask)
+{
+	return __sg_alloc_table_from_pages(sgt, pages, n_pages, offset, size,
+					   SCATTERLIST_MAX_SEGMENT, gfp_mask);
+}
+EXPORT_SYMBOL(sg_alloc_table_from_pages);
+
+#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) | __GFP_ZERO);
+	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);
+
+/**
+ * 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 if @miter is stopped, or not proceeded yet.
+ *   Otherwise, preemption disabled if the SG_MITER_ATOMIC is set.
+ *
+ * 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:
+ *   Preemption disabled if SG_MITER_ATOMIC.  Preemption must stay disabled
+ *   till @miter is stopped.  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:
+ *   Preemption disabled if the SG_MITER_ATOMIC is set.  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) &&
+		    !PageSlab(miter->page))
+			flush_kernel_dcache_page(miter->page);
+
+		if (miter->__flags & SG_MITER_ATOMIC) {
+			WARN_ON_ONCE(preemptible());
+			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 false;
+
+	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);