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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: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Anshuman Khandual 2018-02-15 09:03:56 +05:30 committed by Jens Axboe
parent 468f098734
commit 723fbf563a
1 changed files with 13 additions and 10 deletions
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23
include/linux/scatterlist.h
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@ -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;
}
/**