--- zzzz-none-000/linux-3.10.107/lib/scatterlist.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/lib/scatterlist.c	2021-02-04 17:41:59.000000000 +0000
@@ -56,6 +56,38 @@
 }
 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
@@ -73,16 +105,12 @@
  **/
 struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
 {
-#ifndef ARCH_HAS_SG_CHAIN
-	struct scatterlist *ret = &sgl[nents - 1];
-#else
 	struct scatterlist *sg, *ret = NULL;
 	unsigned int i;
 
 	for_each_sg(sgl, sg, nents, i)
 		ret = sg;
 
-#endif
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(sgl[0].sg_magic != SG_MAGIC);
 	BUG_ON(!sg_is_last(ret));
@@ -165,6 +193,7 @@
  * __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:
@@ -174,7 +203,7 @@
  *
  **/
 void __sg_free_table(struct sg_table *table, unsigned int max_ents,
-		     sg_free_fn *free_fn)
+		     bool skip_first_chunk, sg_free_fn *free_fn)
 {
 	struct scatterlist *sgl, *next;
 
@@ -202,7 +231,10 @@
 		}
 
 		table->orig_nents -= sg_size;
-		free_fn(sgl, alloc_size);
+		if (skip_first_chunk)
+			skip_first_chunk = false;
+		else
+			free_fn(sgl, alloc_size);
 		sgl = next;
 	}
 
@@ -217,7 +249,7 @@
  **/
 void sg_free_table(struct sg_table *table)
 {
-	__sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
+	__sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
 }
 EXPORT_SYMBOL(sg_free_table);
 
@@ -241,19 +273,21 @@
  *
  **/
 int __sg_alloc_table(struct sg_table *table, unsigned int nents,
-		     unsigned int max_ents, gfp_t gfp_mask,
-		     sg_alloc_fn *alloc_fn)
+		     unsigned int max_ents, struct scatterlist *first_chunk,
+		     gfp_t gfp_mask, sg_alloc_fn *alloc_fn)
 {
 	struct scatterlist *sg, *prv;
 	unsigned int left;
 
-#ifndef ARCH_HAS_SG_CHAIN
+	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
 
-	memset(table, 0, sizeof(*table));
-
 	left = nents;
 	prv = NULL;
 	do {
@@ -267,7 +301,12 @@
 
 		left -= sg_size;
 
-		sg = alloc_fn(alloc_size, gfp_mask);
+		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
@@ -322,9 +361,9 @@
 	int ret;
 
 	ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
-			       gfp_mask, sg_kmalloc);
+			       NULL, gfp_mask, sg_kmalloc);
 	if (unlikely(ret))
-		__sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
+		__sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
 
 	return ret;
 }
@@ -453,6 +492,66 @@
 }
 EXPORT_SYMBOL(sg_miter_start);
 
+static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
+{
+	if (!miter->__remaining) {
+		struct scatterlist *sg;
+		unsigned long pgoffset;
+
+		if (!__sg_page_iter_next(&miter->piter))
+			return false;
+
+		sg = miter->piter.sg;
+		pgoffset = miter->piter.sg_pgoffset;
+
+		miter->__offset = pgoffset ? 0 : sg->offset;
+		miter->__remaining = sg->offset + sg->length -
+				(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
@@ -478,22 +577,9 @@
 	 * Get to the next page if necessary.
 	 * __remaining, __offset is adjusted by sg_miter_stop
 	 */
-	if (!miter->__remaining) {
-		struct scatterlist *sg;
-		unsigned long pgoffset;
-
-		if (!__sg_page_iter_next(&miter->piter))
-			return false;
-
-		sg = miter->piter.sg;
-		pgoffset = miter->piter.sg_pgoffset;
+	if (!sg_miter_get_next_page(miter))
+		return false;
 
-		miter->__offset = pgoffset ? 0 : sg->offset;
-		miter->__remaining = sg->offset + sg->length -
-				(pgoffset << PAGE_SHIFT) - miter->__offset;
-		miter->__remaining = min_t(unsigned long, miter->__remaining,
-					   PAGE_SIZE - miter->__offset);
-	}
 	miter->page = sg_page_iter_page(&miter->piter);
 	miter->consumed = miter->length = miter->__remaining;
 
@@ -553,14 +639,15 @@
  * @nents:		 Number of SG entries
  * @buf:		 Where to copy from
  * @buflen:		 The number of bytes to copy
- * @to_buffer: 		 transfer direction (non zero == from an sg list to a
- * 			 buffer, 0 == from a buffer to an sg list
+ * @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.
  *
  **/
-static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
-			     void *buf, size_t buflen, int to_buffer)
+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;
@@ -574,6 +661,9 @@
 
 	sg_miter_start(&miter, sgl, nents, sg_flags);
 
+	if (!sg_miter_skip(&miter, skip))
+		return false;
+
 	local_irq_save(flags);
 
 	while (sg_miter_next(&miter) && offset < buflen) {
@@ -594,6 +684,7 @@
 	local_irq_restore(flags);
 	return offset;
 }
+EXPORT_SYMBOL(sg_copy_buffer);
 
 /**
  * sg_copy_from_buffer - Copy from a linear buffer to an SG list
@@ -606,9 +697,9 @@
  *
  **/
 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
-			   void *buf, size_t buflen)
+			   const void *buf, size_t buflen)
 {
-	return sg_copy_buffer(sgl, nents, buf, buflen, 0);
+	return sg_copy_buffer(sgl, nents, (void *)buf, buflen, 0, false);
 }
 EXPORT_SYMBOL(sg_copy_from_buffer);
 
@@ -625,6 +716,42 @@
 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, 1);
+	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);