Commit 723fbf56 authored by Anshuman Khandual's avatar Anshuman Khandual Committed by Jens Axboe
Browse files

lib/scatterlist: Add SG_CHAIN and SG_END macros for LSB encodings 



This replaces scatterlist->page_link LSB encodings with SG_CHAIN and
SG_END definitions without any functional change.

Signed-off-by: default avatarAnshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 468f0987

include/linux/scatterlist.h

+13 −10
Original line number Diff line number Diff line
@@ -65,16 +65,18 @@ struct sg_table { 
 */



#define SG_MAGIC	0x87654321

#define SG_CHAIN	0x01UL

#define SG_END		0x02UL



/*

 * We overload the LSB of the page pointer to indicate whether it's

 * a valid sg entry, or whether it points to the start of a new scatterlist.

 * Those low bits are there for everyone! (thanks mason :-)

 */

#define sg_is_chain(sg)		((sg)->page_link & 0x01)

#define sg_is_last(sg)		((sg)->page_link & 0x02)

#define sg_is_chain(sg)		((sg)->page_link & SG_CHAIN)

#define sg_is_last(sg)		((sg)->page_link & SG_END)

#define sg_chain_ptr(sg)	\

	((struct scatterlist *) ((sg)->page_link & ~0x03))

	((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))



/**

 * sg_assign_page - Assign a given page to an SG entry
@@ -88,13 +90,13 @@ struct sg_table { 
 **/

static inline void sg_assign_page(struct scatterlist *sg, struct page *page)

{

	unsigned long page_link = sg->page_link & 0x3;

	unsigned long page_link = sg->page_link & (SG_CHAIN | SG_END);



	/*

	 * In order for the low bit stealing approach to work, pages

	 * must be aligned at a 32-bit boundary as a minimum.

	 */

	BUG_ON((unsigned long) page & 0x03);

	BUG_ON((unsigned long) page & (SG_CHAIN | SG_END));

#ifdef CONFIG_DEBUG_SG

	BUG_ON(sg->sg_magic != SG_MAGIC);

	BUG_ON(sg_is_chain(sg));
@@ -130,7 +132,7 @@ static inline struct page *sg_page(struct scatterlist *sg) 
	BUG_ON(sg->sg_magic != SG_MAGIC);

	BUG_ON(sg_is_chain(sg));

#endif

	return (struct page *)((sg)->page_link & ~0x3);

	return (struct page *)((sg)->page_link & ~(SG_CHAIN | SG_END));

}



/**
@@ -178,7 +180,8 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents, 
	 * Set lowest bit to indicate a link pointer, and make sure to clear

	 * the termination bit if it happens to be set.

	 */

	prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;

	prv[prv_nents - 1].page_link = ((unsigned long) sgl | SG_CHAIN)

					& ~SG_END;

}



/**
@@ -198,8 +201,8 @@ static inline void sg_mark_end(struct scatterlist *sg) 
	/*

	 * Set termination bit, clear potential chain bit

	 */

	sg->page_link |= 0x02;

	sg->page_link &= ~0x01;

	sg->page_link |= SG_END;

	sg->page_link &= ~SG_CHAIN;

}



/**
@@ -215,7 +218,7 @@ static inline void sg_unmark_end(struct scatterlist *sg) 
#ifdef CONFIG_DEBUG_SG

	BUG_ON(sg->sg_magic != SG_MAGIC);

#endif

	sg->page_link &= ~0x02;

	sg->page_link &= ~SG_END;

}



/**