[v4,02/38] scatterlist: add generic wrappers for iterating over sgtable objects

Message ID 20200512090058.14910-2-m.szyprowski@samsung.com
State Superseded
Headers show
Series
  • DRM: fix struct sg_table nents vs. orig_nents misuse
Related show

Commit Message

Marek Szyprowski May 12, 2020, 9 a.m.
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>

---
For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsung.com/T/
---
 include/linux/scatterlist.h | 50 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 47 insertions(+), 3 deletions(-)

-- 
1.9.1

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Comments

Robin Murphy May 13, 2020, 1:24 p.m. | #1
On 2020-05-12 10:00 am, Marek Szyprowski wrote:
> 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.


Reviewed-by: Robin Murphy <robin.murphy@arm.com>


> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---

> For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents

> vs. orig_nents misuse' thread:

> https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsung.com/T/

> ---

>   include/linux/scatterlist.h | 50 ++++++++++++++++++++++++++++++++++++++++++---

>   1 file changed, 47 insertions(+), 3 deletions(-)

> 

> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h

> index 6eec50f..4f922af 100644

> --- a/include/linux/scatterlist.h

> +++ b/include/linux/scatterlist.h

> @@ -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 @@ static inline struct page *sg_page_iter_page(struct sg_page_iter *piter)

>    * @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 @@ static inline struct page *sg_page_iter_page(struct sg_page_iter *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_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

>    *

> 

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Patch

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 6eec50f..4f922af 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -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 @@  static inline struct page *sg_page_iter_page(struct sg_page_iter *piter)
  * @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 @@  static inline struct page *sg_page_iter_page(struct sg_page_iter *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_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
  *