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lib/scatterlist: Provide a DMA page iterator

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Commit 2db76d7c3c ("lib/scatterlist: sg_page_iter: support sg lists w/o
backing pages") introduced the sg_page_iter_dma_address() function without
providing a way to use it in the general case. If the sg_dma_len() is not
equal to the sg length callers cannot safely use the
for_each_sg_page/sg_page_iter_dma_address combination.

Resolve this API mistake by providing a DMA specific iterator,
for_each_sg_dma_page(), that uses the right length so
sg_page_iter_dma_address() works as expected with all sglists.

A new iterator type is introduced to provide compile-time safety against
wrongly mixing accessors and iterators.

Acked-by: Christoph Hellwig <hch@lst.de> (for scatterlist)
Acked-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com> (ipu3-cio2)
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
This commit is contained in:
Jason Gunthorpe
2019-01-04 11:40:21 -07:00
parent f368ff188a
commit d901b2760d
5 changed files with 76 additions and 12 deletions
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49
include/linux/scatterlist.h
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@@ -339,12 +339,12 @@ int sg_alloc_table_chained(struct sg_table *table, int nents,
/*
* sg page iterator
*
* Iterates over sg entries page-by-page. On each successful iteration,
* you can call sg_page_iter_page(@piter) and sg_page_iter_dma_address(@piter)
* to get the current page and its dma address. @piter->sg will point to the
* sg holding this page and @piter->sg_pgoffset to the page's page offset
* within the sg. The iteration will stop either when a maximum number of sg
* entries was reached or a terminating sg (sg_last(sg) == true) was reached.
* Iterates over sg entries page-by-page. On each successful iteration, you
* can call sg_page_iter_page(@piter) to get the current page and its dma
* address. @piter->sg will point to the sg holding this page and
* @piter->sg_pgoffset to the page's page offset within the sg. The iteration
* will stop either when a maximum number of sg entries was reached or a
* terminating sg (sg_last(sg) == true) was reached.
*/
struct sg_page_iter {
struct scatterlist *sg; /* sg holding the page */
@@ -356,7 +356,19 @@ struct sg_page_iter {
* next step */
};
/*
* sg page iterator for DMA addresses
*
* This is the same as sg_page_iter however you can call
* sg_page_iter_dma_address(@dma_iter) to get the page's DMA
* address. sg_page_iter_page() cannot be called on this iterator.
*/
struct sg_dma_page_iter {
struct sg_page_iter base;
};
bool __sg_page_iter_next(struct sg_page_iter *piter);
bool __sg_page_iter_dma_next(struct sg_dma_page_iter *dma_iter);
void __sg_page_iter_start(struct sg_page_iter *piter,
struct scatterlist *sglist, unsigned int nents,
unsigned long pgoffset);
@@ -372,11 +384,13 @@ static inline struct page *sg_page_iter_page(struct sg_page_iter *piter)
/**
* sg_page_iter_dma_address - get the dma address of the current page held by
* the page iterator.
* @piter: page iterator holding the page
* @dma_iter: page iterator holding the page
*/
static inline dma_addr_t sg_page_iter_dma_address(struct sg_page_iter *piter)
static inline dma_addr_t
sg_page_iter_dma_address(struct sg_dma_page_iter *dma_iter)
{
return sg_dma_address(piter->sg) + (piter->sg_pgoffset << PAGE_SHIFT);
return sg_dma_address(dma_iter->base.sg) +
(dma_iter->base.sg_pgoffset << PAGE_SHIFT);
}
/**
@@ -385,11 +399,28 @@ static inline dma_addr_t sg_page_iter_dma_address(struct sg_page_iter *piter)
* @piter: page iterator to hold current page, sg, sg_pgoffset
* @nents: maximum number of sg entries to iterate over
* @pgoffset: starting page offset
*
* Callers may use sg_page_iter_page() to get each page pointer.
*/
#define for_each_sg_page(sglist, piter, nents, pgoffset) \
for (__sg_page_iter_start((piter), (sglist), (nents), (pgoffset)); \
__sg_page_iter_next(piter);)
/**
* 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_nents: maximum number of sg entries to iterate over, this is the value
* returned from dma_map_sg
* @pgoffset: starting page offset
*
* Callers may use sg_page_iter_dma_address() to get each page's DMA address.
*/
#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);)
/*
* Mapping sg iterator
*