[SCSI] block: add sg buffer copy helper functions

This patch adds new three helper functions to copy data between an SG
list and a linear buffer.

- sg_copy_from_buffer copies data from linear buffer to an SG list

- sg_copy_to_buffer copies data from an SG list to a linear buffer

When the APIs copy data from a linear buffer to an SG list,
flush_kernel_dcache_page is called. 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@lab.ntt.co.jp>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index a3d567a974e8319de915ebf48423a434fca3880f..71fc8136004892903bebc866f5aee249e0de06d7 100644 (file)
--- 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);
 
+size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
+                          void *buf, size_t buflen);
+size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
+                        void *buf, size_t 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 acca4901046c45b055d98ff0b5858a3bc4056ff4..b80c21100d783ceeee87fa828600d90b322120ab 100644 (file)
--- 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 +293,104 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
        return ret;
 }
 EXPORT_SYMBOL(sg_alloc_table);
+
+/**
+ * sg_copy_buffer - Copy data between a linear buffer and an SG list
+ * @sgl:                The SG list
+ * @nents:              Number of SG entries
+ * @buf:                Where to copy from
+ * @buflen:             The number of bytes to copy
+ * @to_buffer:                  transfer direction (non zero == from an sg list to a
+ *                      buffer, 0 == from a buffer to an sg list
+ *
+ * Returns the number of copied bytes.
+ *
+ **/
+static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
+                            void *buf, size_t buflen, int to_buffer)
+{
+       struct scatterlist *sg;
+       size_t 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_buffer)
+                               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 a linear buffer to an SG list
+ * @sgl:                The SG list
+ * @nents:              Number of SG entries
+ * @buf:                Where to copy from
+ * @buflen:             The number of bytes to copy
+ *
+ * Returns the number of copied bytes.
+ *
+ **/
+size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
+                          void *buf, size_t buflen)
+{
+       return sg_copy_buffer(sgl, nents, buf, buflen, 0);
+}
+EXPORT_SYMBOL(sg_copy_from_buffer);
+
+/**
+ * sg_copy_to_buffer - Copy from an SG list to a linear buffer
+ * @sgl:                The SG list
+ * @nents:              Number of SG entries
+ * @buf:                Where to copy to
+ * @buflen:             The number of bytes to copy
+ *
+ * Returns the number of copied bytes.
+ *
+ **/
+size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
+                        void *buf, size_t buflen)
+{
+       return sg_copy_buffer(sgl, nents, buf, buflen, 1);
+}
+EXPORT_SYMBOL(sg_copy_to_buffer);