Commit b1adaf65 authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by James Bottomley
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[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: default avatarFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: default avatarJens Axboe <jens.axboe@oracle.com>
Signed-off-by: default avatarJames Bottomley <James.Bottomley@HansenPartnership.com>
parent 78b4b05d
......@@ -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.
......
......@@ -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);
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