Add chained sg support to linux/scatterlist.h (70eb8040) · Commits · 戴 / test

include/linux/scatterlist.h

+77 −2

Original line number	Diff line number	Diff line
		@@ -20,8 +20,36 @@ static inline void sg_init_one(struct scatterlist sg, const void buf,
		sg_set_buf(sg, buf, buflen);
		}

		#define sg_next(sg) ((sg) + 1)
		#define sg_last(sg, nents) (&(sg[(nents) - 1]))
		/*
		* 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) ((unsigned long) (sg)->page & 0x01)
		#define sg_chain_ptr(sg) \
		((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01))

		/**
		* sg_next - return the next scatterlist entry in a list
		* @sg: The current sg entry
		*
		* Usually the next entry will be @sg@ + 1, but if this sg element is part
		* of a chained scatterlist, it could jump to the start of a new
		* scatterlist array.
		*
		* Note that the caller must ensure that there are further entries after
		* the current entry, this function will NOT return NULL for an end-of-list.
		*
		*/
		static inline struct scatterlist sg_next(struct scatterlist sg)
		{
		sg++;

		if (unlikely(sg_is_chain(sg)))
		sg = sg_chain_ptr(sg);

		return sg;
		}

		/*
		* Loop over each sg element, following the pointer to a new list if necessary
		@@ -29,4 +57,51 @@ static inline void sg_init_one(struct scatterlist sg, const void buf,
		#define for_each_sg(sglist, sg, nr, __i) \
		for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))

		/**
		* sg_last - return the last scatterlist entry in a list
		* @sgl: First entry in the scatterlist
		* @nents: Number of entries in the scatterlist
		*
		* Should only be used casually, it (currently) scan the entire list
		* to get the last entry.
		*
		* Note that the @sgl@ pointer passed in need not be the first one,
		* the important bit is that @nents@ denotes the number of entries that
		* exist from @sgl@.
		*
		*/
		static inline struct scatterlist sg_last(struct scatterlist sgl,
		unsigned int nents)
		{
		#ifndef ARCH_HAS_SG_CHAIN
		struct scatterlist *ret = &sgl[nents - 1];
		#else
		struct scatterlist sg, ret = NULL;
		int i;

		for_each_sg(sgl, sg, nents, i)
		ret = sg;

		#endif
		return ret;
		}

		/**
		* sg_chain - Chain two sglists together
		* @prv: First scatterlist
		* @prv_nents: Number of entries in prv
		* @sgl: Second scatterlist
		*
		* Links @prv@ and @sgl@ together, to form a longer scatterlist.
		*
		*/
		static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
		struct scatterlist *sgl)
		{
		#ifndef ARCH_HAS_SG_CHAIN
		BUG();
		#endif
		prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl \| 0x01);
		}

		#endif /* _LINUX_SCATTERLIST_H */

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