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authorImre Deak <imre.deak@intel.com>2013-02-27 17:02:56 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-27 19:10:10 -0800
commita321e91b6d73ed011ffceed384c40d2785cf723b (patch)
tree525598b796028211e615676f5e3182c630f992f1 /lib
parent5d96bf4d928c883635774d0aba1773f275de055c (diff)
downloadlinux-a321e91b6d73ed011ffceed384c40d2785cf723b.tar.gz
lib/scatterlist: add simple page iterator
Add an iterator to walk through a scatter list a page at a time starting at a specific page offset. As opposed to the mapping iterator this is meant to be small, performing well even in simple loops like collecting all pages on the scatterlist into an array or setting up an iommu table based on the pages' DMA address. 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> Tested-by: Stephen Warren <swarren@wwwdotorg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/scatterlist.c38
1 files changed, 38 insertions, 0 deletions
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 7874b01e816..a1d15647d7d 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -394,6 +394,44 @@ int sg_alloc_table_from_pages(struct sg_table *sgt,
}
EXPORT_SYMBOL(sg_alloc_table_from_pages);
+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->page = NULL;
+ 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;
+ }
+ piter->page = nth_page(sg_page(piter->sg), piter->sg_pgoffset);
+
+ 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