This patch adds new two helper functions to copy data between an SG
table and liner buffer.
- sg_copy_from_buffer copies data from liner buffer to an SG table
- sg_copy_to_buffer copies data from an SG table to liner buffer
sg_copy_from_buffer always call flush_kernel_dcache_page. It's not
necessary for everyone but it's a no-op on most architectures and in
general the API is not used in performance critical path.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
---
include/linux/scatterlist.h | 5 ++
lib/scatterlist.c | 90 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 95 insertions(+), 0 deletions(-)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index a3d567a..ab6c672 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -213,6 +213,11 @@ int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t,
sg_alloc_fn *);
int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
+int sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
+ void *buf, int buflen);
+int sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
+ void *buf, int buflen);
+
/*
* Maximum number of entries that will be allocated in one piece, if
* a list larger than this is required then chaining will be utilized.
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index acca490..63e9c35 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -8,6 +8,7 @@
*/
#include <linux/module.h>
#include <linux/scatterlist.h>
+#include <linux/highmem.h>
/**
* sg_next - return the next scatterlist entry in a list
@@ -292,3 +293,92 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
return ret;
}
EXPORT_SYMBOL(sg_alloc_table);
+
+static int sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
+ void *buf, int buflen, int to_buf)
+{
+ struct scatterlist *sg;
+ unsigned long buf_off = 0;
+ int i;
+
+ WARN_ON(!irqs_disabled());
+
+ for_each_sg(sgl, sg, nents, i) {
+ struct page *page;
+ int n = 0;
+ unsigned int sg_off = sg->offset;
+ unsigned int sg_copy = sg->length;
+
+ if (sg_copy > buflen)
+ sg_copy = buflen;
+ buflen -= sg_copy;
+
+ while (sg_copy > 0) {
+ unsigned int page_copy;
+ void *p;
+
+ page_copy = PAGE_SIZE - sg_off;
+ if (page_copy > sg_copy)
+ page_copy = sg_copy;
+
+ page = nth_page(sg_page(sg), n);
+ p = kmap_atomic(page, KM_BIO_SRC_IRQ);
+
+ if (to_buf)
+ memcpy(buf + buf_off, p + sg_off, page_copy);
+ else {
+ memcpy(p + sg_off, buf + buf_off, page_copy);
+ flush_kernel_dcache_page(page);
+ }
+
+ kunmap_atomic(p, KM_BIO_SRC_IRQ);
+
+ buf_off += page_copy;
+ sg_off += page_copy;
+ if (sg_off == PAGE_SIZE) {
+ sg_off = 0;
+ n++;
+ }
+ sg_copy -= page_copy;
+ }
+
+ if (!buflen)
+ break;
+ }
+
+ return buf_off;
+}
+
+/**
+ * sg_copy_from_buffer - Copy from liner buffer to an SG table
+ * @sgl: The SG table
+ * @nents: Number of SG entries
+ * @buf: Where to copy from
+ * @buflen: The number of bytes to copy
+ *
+ * Returns the number of copied byte.
+ *
+ **/
+int sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
+ void *buf, int buflen)
+{
+ return sg_copy_buffer(sgl, nents, buf, buflen, 0);
+}
+EXPORT_SYMBOL(sg_copy_from_buffer);
+
+/**
+ * sg_copy_to_buffer - Copy from an SG table to liner buffer
+ * @sgl: The SG table
+ * @nents: Number of SG entries
+ * @buf: Where to copy to
+ * @buflen: The number of bytes to copy
+ *
+ * Returns the number of copied byte.
+ *
+ **/
+int sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
+ void *buf, int buflen)
+{
+ return sg_copy_buffer(sgl, nents, buf, buflen, 1);
+}
+EXPORT_SYMBOL(sg_copy_to_buffer);
--
1.5.3.7
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