Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit b1adaf65 authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by James Bottomley
Browse files

[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

include/linux/scatterlist.h

+5 −0
Original line number Diff line number Diff line
@@ -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.

lib/scatterlist.c

+102 −0
Original line number Diff line number Diff line
@@ -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);