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Subject[PATCH 01/14] scatterlist: add sg_kmap_atomic / sg_kunmap_atomic helpers
Date
This avoids bug prone open coding of the sg offset handling and
also helps to document the limitations of mapping scatterlist
entries.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
include/linux/scatterlist.h | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index b96f0d0b5b8f..524cd8448a48 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -2,6 +2,7 @@
#ifndef _LINUX_SCATTERLIST_H
#define _LINUX_SCATTERLIST_H

+#include <linux/highmem.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/bug.h>
@@ -239,6 +240,31 @@ static inline void *sg_virt(struct scatterlist *sg)
return page_address(sg_page(sg)) + sg->offset;
}

+/**
+ * sg_kmap_atomic - map a S/G list entry to a kernel address
+ * @sg: scatterlist entry
+ *
+ * Return a kernel address for scatterlist entry by kmapping it. Note that
+ * this function must only be called on scatterlist entries that do not span
+ * multiple pages.
+ */
+static inline void *sg_kmap_atomic(struct scatterlist *sg)
+{
+ if (WARN_ON_ONCE(sg->offset + sg->length > PAGE_SIZE))
+ return NULL;
+ return kmap_atomic(sg_page(sg)) + sg->offset;
+}
+
+/**
+ * sg_kunmap_atomic - unmap a S/G list entry to a kernel address
+ * @sg: scatterlist entry
+ * @ptr: address returned from sg_kmap_atomic
+ */
+static inline void sg_kunmap_atomic(struct scatterlist *sg, void *ptr)
+{
+ kunmap_atomic(ptr - sg->offset);
+}
+
/**
* sg_init_marker - Initialize markers in sg table
* @sgl: The SG table
--
2.20.1
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