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scatterlist: add generic wrappers for iterating over sgtable objects 

struct sg_table is a common structure used for describing a memory
buffer. It consists of a scatterlist with memory pages and DMA addresses
(sgl entry), as well as the number of scatterlist entries: CPU pages
(orig_nents entry) and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling the scatterlist iterating functions with a wrong number
of the entries.

To avoid such issues, lets introduce a common wrappers operating directly
on the struct sg_table objects, which take care of the proper use of
the nents and orig_nents entries.

While touching this, lets clarify some ambiguities in the comments for
the existing for_each helpers.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
alistair/sunxi64-5.8
Marek Szyprowski 2020-05-13 15:32:09 +02:00 committed by Christoph Hellwig
parent d9d200bceb
commit 709d6d73c7
1 changed files with 47 additions and 3 deletions
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50
include/linux/scatterlist.h
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@ -151,6 +151,20 @@ static inline void sg_set_buf(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))
/*
* Loop over each sg element in the given sg_table object.
*/
#define for_each_sgtable_sg(sgt, sg, i) \
for_each_sg(sgt->sgl, sg, sgt->orig_nents, i)
/*
* Loop over each sg element in the given *DMA mapped* sg_table object.
* Please use sg_dma_address(sg) and sg_dma_len(sg) to extract DMA addresses
* of the each element.
*/
#define for_each_sgtable_dma_sg(sgt, sg, i) \
for_each_sg(sgt->sgl, sg, sgt->nents, i)
/**
* sg_chain - Chain two sglists together
* @prv: First scatterlist
@ -401,9 +415,10 @@ sg_page_iter_dma_address(struct sg_dma_page_iter *dma_iter)
* @sglist: sglist to iterate over
* @piter: page iterator to hold current page, sg, sg_pgoffset
* @nents: maximum number of sg entries to iterate over
* @pgoffset: starting page offset
* @pgoffset: starting page offset (in pages)
*
* Callers may use sg_page_iter_page() to get each page pointer.
* In each loop it operates on PAGE_SIZE unit.
*/
#define for_each_sg_page(sglist, piter, nents, pgoffset) \
for (__sg_page_iter_start((piter), (sglist), (nents), (pgoffset)); \
@ -412,18 +427,47 @@ sg_page_iter_dma_address(struct sg_dma_page_iter *dma_iter)
/**
* for_each_sg_dma_page - iterate over the pages of the given sg list
* @sglist: sglist to iterate over
* @dma_iter: page iterator to hold current page
* @dma_iter: DMA page iterator to hold current page
* @dma_nents: maximum number of sg entries to iterate over, this is the value
* returned from dma_map_sg
* @pgoffset: starting page offset
* @pgoffset: starting page offset (in pages)
*
* Callers may use sg_page_iter_dma_address() to get each page's DMA address.
* In each loop it operates on PAGE_SIZE unit.
*/
#define for_each_sg_dma_page(sglist, dma_iter, dma_nents, pgoffset) \
for (__sg_page_iter_start(&(dma_iter)->base, sglist, dma_nents, \
pgoffset); \
__sg_page_iter_dma_next(dma_iter);)
/**
* for_each_sgtable_page - iterate over all pages in the sg_table object
* @sgt: sg_table object to iterate over
* @piter: page iterator to hold current page
* @pgoffset: starting page offset (in pages)
*
* Iterates over the all memory pages in the buffer described by
* a scatterlist stored in the given sg_table object.
* See also for_each_sg_page(). In each loop it operates on PAGE_SIZE unit.
*/
#define for_each_sgtable_page(sgt, piter, pgoffset) \
for_each_sg_page(sgt->sgl, piter, sgt->orig_nents, pgoffset)
/**
* for_each_sgtable_dma_page - iterate over the DMA mapped sg_table object
* @sgt: sg_table object to iterate over
* @dma_iter: DMA page iterator to hold current page
* @pgoffset: starting page offset (in pages)
*
* Iterates over the all DMA mapped pages in the buffer described by
* a scatterlist stored in the given sg_table object.
* See also for_each_sg_dma_page(). In each loop it operates on PAGE_SIZE
* unit.
*/
#define for_each_sgtable_dma_page(sgt, dma_iter, pgoffset) \
for_each_sg_dma_page(sgt->sgl, dma_iter, sgt->nents, pgoffset)
/*
* Mapping sg iterator
*