lib/scatterlist: introduce sg_pcopy_from_buffer() and sg_pcopy_to_buffer()

The only difference between sg_pcopy_{from,to}_buffer() and
sg_copy_{from,to}_buffer() is an additional argument that specifies the
number of bytes to skip the SG list before copying.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Horia Geanta <horia.geanta@freescale.com>
Cc: Imre Deak <imre.deak@intel.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 83 insertions, 5 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index c35b929435f3..129a82f707df 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -476,6 +476,43 @@ static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
 }
 
 /**
+ * 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.
+ */
+static 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;
+}
+
+/**
  * sg_miter_next - proceed mapping iterator to the next mapping
  * @miter: sg mapping iter to proceed
  *
@@ -561,14 +598,16 @@ EXPORT_SYMBOL(sg_miter_stop);
  * @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)
+                             void *buf, size_t buflen, off_t skip,
+                             bool to_buffer)
 {
         unsigned int offset = 0;
         struct sg_mapping_iter miter;
@@ -582,6 +621,9 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 
         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) {
@@ -616,7 +658,7 @@ static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
                            void *buf, size_t buflen)
 {
-        return sg_copy_buffer(sgl, nents, buf, buflen, 0);
+        return sg_copy_buffer(sgl, nents, buf, buflen, 0, false);
 }
 EXPORT_SYMBOL(sg_copy_from_buffer);
 
@@ -633,6 +675,42 @@ EXPORT_SYMBOL(sg_copy_from_buffer);
 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
+ * @skip:                Number of bytes to skip before copying
+ * @buflen:              The number of bytes to copy
+ *
+ * Returns the number of copied bytes.
+ *
+ **/
+size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
+                            void *buf, size_t buflen, off_t skip)
+{
+        return sg_copy_buffer(sgl, nents, 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
+ * @skip:                Number of bytes to skip before copying
+ * @buflen:              The number of bytes to copy
+ *
+ * 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);