linux-kernel - [RFC PATCH 5/8] scatterlist: introduce sg_unmark

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Date:	Thu,  7 Feb 2013 13:22:29 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Wanlong Gao <gaowanlong@...fujitsu.com>, asias@...hat.com,
	Rusty Russell <rusty@...tcorp.com.au>, mst@...hat.com,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	Jens Axboe <axboe@...nel.dk>
Subject: [RFC PATCH 5/8] scatterlist: introduce sg_unmark_end

This is useful in places that recycle the same scatterlist multiple
times, and do not want to incur the cost of sg_init_table every
time in hot paths.

Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
	Jens, could you give your Acked-by for this patch?

 block/blk-integrity.c       |    2 +-
 block/blk-merge.c           |    2 +-
 include/linux/scatterlist.h |   16 ++++++++++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/block/blk-integrity.c b/block/blk-integrity.c
index da2a818..0f5004f 100644
--- a/block/blk-integrity.c
+++ b/block/blk-integrity.c
@@ -110,7 +110,7 @@ new_segment:
 			if (!sg)
 				sg = sglist;
 			else {
-				sg->page_link &= ~0x02;
+				sg_unmark_end(sg);
 				sg = sg_next(sg);
 			}
 
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 936a110..5f24482 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -143,7 +143,7 @@ new_segment:
 			 * termination bit to avoid doing a full
 			 * sg_init_table() in drivers for each command.
 			 */
-			(*sg)->page_link &= ~0x02;
+			sg_unmark_end(*sg);
 			*sg = sg_next(*sg);
 		}
 
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 4bd6c06..9b83784 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -172,6 +172,22 @@ static inline void sg_mark_end(struct scatterlist *sg)
 }
 
 /**
+ * sg_unmark_end - Undo setting the end of the scatterlist
+ * @sg:		 SG entryScatterlist
+ *
+ * Description:
+ *   Removes the termination marker from the given entry of the scatterlist.
+ *
+ **/
+static inline void sg_unmark_end(struct scatterlist *sg)
+{
+#ifdef CONFIG_DEBUG_SG
+	BUG_ON(sg->sg_magic != SG_MAGIC);
+#endif
+	sg->page_link &= ~0x02;
+}
+
+/**
  * sg_phys - Return physical address of an sg entry
  * @sg:	     SG entry
  *
-- 
1.7.1


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