lib/scatterlist: use page iterator in the mapping iterator

For better code reuse use the newly added page iterator to iterate
through the pages.  The offset, length within the page is still
calculated by the mapping iterator as well as the actual mapping.  Idea
from Tejun Heo.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Cc: Maxim Levitsky <maximlevitsky@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 25 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index a1d15647d7db..b83c144d731f 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -449,9 +449,7 @@ void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 {
         memset(miter, 0, sizeof(struct sg_mapping_iter));
 
-        miter->__sg = sgl;
-        miter->__nents = nents;
-        miter->__offset = 0;
+        __sg_page_iter_start(&miter->piter, sgl, nents, 0);
         WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
         miter->__flags = flags;
 }
@@ -476,36 +474,35 @@ EXPORT_SYMBOL(sg_miter_start);
  */
 bool sg_miter_next(struct sg_mapping_iter *miter)
 {
-        unsigned int off, len;
-
-        /* check for end and drop resources from the last iteration */
-        if (!miter->__nents)
-                return false;
-
         sg_miter_stop(miter);
 
-        /* get to the next sg if necessary.  __offset is adjusted by stop */
-        while (miter->__offset == miter->__sg->length) {
-                if (--miter->__nents) {
-                        miter->__sg = sg_next(miter->__sg);
-                        miter->__offset = 0;
-                } else
+        /*
+         * 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;
-        }
 
-        /* map the next page */
-        off = miter->__sg->offset + miter->__offset;
-        len = miter->__sg->length - miter->__offset;
+                sg = miter->piter.sg;
+                pgoffset = miter->piter.sg_pgoffset;
 
-        miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
-        off &= ~PAGE_MASK;
-        miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
-        miter->consumed = miter->length;
+                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 = miter->piter.page;
+        miter->consumed = miter->length = miter->__remaining;
 
         if (miter->__flags & SG_MITER_ATOMIC)
-                miter->addr = kmap_atomic(miter->page) + off;
+                miter->addr = kmap_atomic(miter->page) + miter->__offset;
         else
-                miter->addr = kmap(miter->page) + off;
+                miter->addr = kmap(miter->page) + miter->__offset;
 
         return true;
 }
@@ -532,6 +529,7 @@ void sg_miter_stop(struct sg_mapping_iter *miter)
         /* 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_kernel_dcache_page(miter->page);