scatterlist: introduce sg_nents_for_len (cfaed10d) · Commits · 戴 / test

When performing a dma_map_sg() call, the number of sg entries to map is required. Using sg_nents to retrieve the number of sg entries will return the total number of entries in the sg list up to the entry marked as the end. If there happen to be unused entries in the list, these will still be counted. Some dma_map_sg() implementations will not handle the unused entries correctly (lib/swiotlb.c) and execute a BUG_ON. The sg_nents_for_len() function will traverse the sg list and return the number of entries required to satisfy the supplied length argument. This can then be supplied to the dma_map_sg() call to successfully map the sg. Signed-off-by:

Tom Lendacky <thomas.lendacky@amd.com> Signed-off-by:

Herbert Xu <herbert@gondor.apana.org.au>

include/linux/scatterlist.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -221,6 +221,7 @@ static inline void sg_virt(struct scatterlist sg)
		}

		int sg_nents(struct scatterlist *sg);
		int sg_nents_for_len(struct scatterlist *sg, u64 len);
		struct scatterlist sg_next(struct scatterlist );
		struct scatterlist sg_last(struct scatterlist s, unsigned int);
		void sg_init_table(struct scatterlist *, unsigned int);

lib/scatterlist.c

+32 −0

Original line number	Diff line number	Diff line
		@@ -56,6 +56,38 @@ int sg_nents(struct scatterlist *sg)
		}
		EXPORT_SYMBOL(sg_nents);

		/**
		* sg_nents_for_len - return total count of entries in scatterlist
		* needed to satisfy the supplied length
		* @sg: The scatterlist
		* @len: The total required length
		*
		* Description:
		* Determines the number of entries in sg that are required to meet
		* the supplied length, taking into acount chaining as well
		*
		* Returns:
		* the number of sg entries needed, negative error on failure
		*
		**/
		int sg_nents_for_len(struct scatterlist *sg, u64 len)
		{
		int nents;
		u64 total;

		if (!len)
		return 0;

		for (nents = 0, total = 0; sg; sg = sg_next(sg)) {
		nents++;
		total += sg->length;
		if (total >= len)
		return nents;
		}

		return -EINVAL;
		}
		EXPORT_SYMBOL(sg_nents_for_len);

		/**
		* sg_last - return the last scatterlist entry in a list

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