From a321e91b6d73ed011ffceed384c40d2785cf723b Mon Sep 17 00:00:00 2001 From: Imre Deak Date: Wed, 27 Feb 2013 17:02:56 -0800 Subject: 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 Cc: Maxim Levitsky Cc: Tejun Heo Cc: Daniel Vetter Tested-by: Stephen Warren Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/scatterlist.c | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) (limited to 'lib') diff --git a/lib/scatterlist.c b/lib/scatterlist.c index 7874b01e816e..a1d15647d7db 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 -- cgit v1.2.3-59-g8ed1b