include/linux/scatterlist.h - kernel/msm-5.4 - Gitiles

 #ifndef _LINUX_SCATTERLIST_H
 #define _LINUX_SCATTERLIST_H

 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/bug.h>
 #include <linux/mm.h>
 #include <asm/io.h>

 struct scatterlist {
 #ifdef CONFIG_DEBUG_SG
 	unsigned long	sg_magic;
 #endif
 	unsigned long	page_link;
 	unsigned int	offset;
 	unsigned int	length;
 	dma_addr_t	dma_address;
 #ifdef CONFIG_NEED_SG_DMA_LENGTH
 	unsigned int	dma_length;
 #endif
 };

 /*
  * These macros should be used after a dma_map_sg call has been done
  * to get bus addresses of each of the SG entries and their lengths.
  * You should only work with the number of sg entries dma_map_sg
  * returns, or alternatively stop on the first sg_dma_len(sg) which
  * is 0.
  */
 #define sg_dma_address(sg)	((sg)->dma_address)

 #ifdef CONFIG_NEED_SG_DMA_LENGTH
 #define sg_dma_len(sg)		((sg)->dma_length)
 #else
 #define sg_dma_len(sg)		((sg)->length)
 #endif

 struct sg_table {
 	struct scatterlist *sgl;	/* the list */
 	unsigned int nents;		/* number of mapped entries */
 	unsigned int orig_nents;	/* original size of list */
 };

 /*
  * Notes on SG table design.
  *
  * We use the unsigned long page_link field in the scatterlist struct to place
  * the page pointer AND encode information about the sg table as well. The two
  * lower bits are reserved for this information.
  *
  * If bit 0 is set, then the page_link contains a pointer to the next sg
  * table list. Otherwise the next entry is at sg + 1.
  *
  * If bit 1 is set, then this sg entry is the last element in a list.
  *
  * See sg_next().
  *
  */

 #define SG_MAGIC	0x87654321

 /*
  * 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)		((sg)->page_link & 0x01)
 #define sg_is_last(sg)		((sg)->page_link & 0x02)
 #define sg_chain_ptr(sg)	\
 	((struct scatterlist *) ((sg)->page_link & ~0x03))

 /**
  * sg_assign_page - Assign a given page to an SG entry
  * @sg:		    SG entry
  * @page:	    The page
  *
  * Description:
  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  *   variant.
  *
  **/
 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
 {
 	unsigned long page_link = sg->page_link & 0x3;

 	/*
 	 * In order for the low bit stealing approach to work, pages
 	 * must be aligned at a 32-bit boundary as a minimum.
 	 */
 	BUG_ON((unsigned long) page & 0x03);
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(sg->sg_magic != SG_MAGIC);
 	BUG_ON(sg_is_chain(sg));
 #endif
 	sg->page_link = page_link | (unsigned long) page;
 }

 /**
  * sg_set_page - Set sg entry to point at given page
  * @sg:		 SG entry
  * @page:	 The page
  * @len:	 Length of data
  * @offset:	 Offset into page
  *
  * Description:
  *   Use this function to set an sg entry pointing at a page, never assign
  *   the page directly. We encode sg table information in the lower bits
  *   of the page pointer. See sg_page() for looking up the page belonging
  *   to an sg entry.
  *
  **/
 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
 			       unsigned int len, unsigned int offset)
 {
 	sg_assign_page(sg, page);
 	sg->offset = offset;
 	sg->length = len;
 }

 static inline struct page *sg_page(struct scatterlist *sg)
 {
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(sg->sg_magic != SG_MAGIC);
 	BUG_ON(sg_is_chain(sg));
 #endif
 	return (struct page *)((sg)->page_link & ~0x3);
 }

 /**
  * sg_set_buf - Set sg entry to point at given data
  * @sg:		 SG entry
  * @buf:	 Data
  * @buflen:	 Data length
  *
  **/
 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
 			      unsigned int buflen)
 {
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(!virt_addr_valid(buf));
 #endif
 	sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
 }

 /*
  * Loop over each sg element, following the pointer to a new list if necessary
  */
 #define for_each_sg(sglist, sg, nr, __i)	\
 	for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))

 /**
  * sg_chain - Chain two sglists together
  * @prv:	First scatterlist
  * @prv_nents:	Number of entries in prv
  * @sgl:	Second scatterlist
  *
  * Description:
  *   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)
 {
 	/*
 	 * offset and length are unused for chain entry.  Clear them.
 	 */
 	prv[prv_nents - 1].offset = 0;
 	prv[prv_nents - 1].length = 0;

 	/*
 	 * Set lowest bit to indicate a link pointer, and make sure to clear
 	 * the termination bit if it happens to be set.
 	 */
 	prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
 }

 /**
  * sg_mark_end - Mark the end of the scatterlist
  * @sg:		 SG entryScatterlist
  *
  * Description:
  *   Marks the passed in sg entry as the termination point for the sg
  *   table. A call to sg_next() on this entry will return NULL.
  *
  **/
 static inline void sg_mark_end(struct scatterlist *sg)
 {
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(sg->sg_magic != SG_MAGIC);
 #endif
 	/*
 	 * Set termination bit, clear potential chain bit
 	 */
 	sg->page_link |= 0x02;
 	sg->page_link &= ~0x01;
 }

 /**
  * sg_unmark_end - Undo setting the end of the scatterlist
  * @sg:		 SG entryScatterlist
  *
  * Description:
  *   Removes the termination marker from the given entry of the scatterlist.
  *
  **/
 static inline void sg_unmark_end(struct scatterlist *sg)
 {
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(sg->sg_magic != SG_MAGIC);
 #endif
 	sg->page_link &= ~0x02;
 }

 /**
  * sg_phys - Return physical address of an sg entry
  * @sg:	     SG entry
  *
  * Description:
  *   This calls page_to_phys() on the page in this sg entry, and adds the
  *   sg offset. The caller must know that it is legal to call page_to_phys()
  *   on the sg page.
  *
  **/
 static inline dma_addr_t sg_phys(struct scatterlist *sg)
 {
 	return page_to_phys(sg_page(sg)) + sg->offset;
 }

 /**
  * sg_virt - Return virtual address of an sg entry
  * @sg:      SG entry
  *
  * Description:
  *   This calls page_address() on the page in this sg entry, and adds the
  *   sg offset. The caller must know that the sg page has a valid virtual
  *   mapping.
  *
  **/
 static inline void *sg_virt(struct scatterlist *sg)
 {
 	return page_address(sg_page(sg)) + sg->offset;
 }

 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);
 void sg_init_one(struct scatterlist *, const void *, unsigned int);
 int sg_split(struct scatterlist *in, const int in_mapped_nents,
 	     const off_t skip, const int nb_splits,
 	     const size_t *split_sizes,
 	     struct scatterlist **out, int *out_mapped_nents,
 	     gfp_t gfp_mask);

 typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
 typedef void (sg_free_fn)(struct scatterlist *, unsigned int);

 void __sg_free_table(struct sg_table *, unsigned int, bool, sg_free_fn *);
 void sg_free_table(struct sg_table *);
 int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int,
 		     struct scatterlist *, gfp_t, sg_alloc_fn *);
 int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
 int sg_alloc_table_from_pages(struct sg_table *sgt,
 	struct page **pages, unsigned int n_pages,
 	unsigned long offset, unsigned long size,
 	gfp_t gfp_mask);

 size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
 		      size_t buflen, off_t skip, bool to_buffer);

 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 			   const void *buf, size_t buflen);
 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 			 void *buf, size_t buflen);

 size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 			    const void *buf, size_t buflen, off_t skip);
 size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 			  void *buf, size_t buflen, off_t skip);
 size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
 		       size_t buflen, off_t skip);

 /*
  * Maximum number of entries that will be allocated in one piece, if
  * a list larger than this is required then chaining will be utilized.
  */
 #define SG_MAX_SINGLE_ALLOC		(PAGE_SIZE / sizeof(struct scatterlist))

 /*
  * The maximum number of SG segments that we will put inside a
  * scatterlist (unless chaining is used). Should ideally fit inside a
  * single page, to avoid a higher order allocation.  We could define this
  * to SG_MAX_SINGLE_ALLOC to pack correctly at the highest order.  The
  * minimum value is 32
  */
 #define SG_CHUNK_SIZE	128

 /*
  * Like SG_CHUNK_SIZE, but for archs that have sg chaining. This limit
  * is totally arbitrary, a setting of 2048 will get you at least 8mb ios.
  */
 #ifdef CONFIG_ARCH_HAS_SG_CHAIN
 #define SG_MAX_SEGMENTS	2048
 #else
 #define SG_MAX_SEGMENTS	SG_CHUNK_SIZE
 #endif

 #ifdef CONFIG_SG_POOL
 void sg_free_table_chained(struct sg_table *table, bool first_chunk);
 int sg_alloc_table_chained(struct sg_table *table, int nents,
 			   struct scatterlist *first_chunk);
 #endif

 /*
  * 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.
  */
 struct sg_page_iter {
 	struct scatterlist	*sg;		/* sg holding the page */
 	unsigned int		sg_pgoffset;	/* page offset within the sg */

 	/* these are internal states, keep away */
 	unsigned int		__nents;	/* remaining sg entries */
 	int			__pg_advance;	/* nr pages to advance at the
 						 * next step */
 };

 bool __sg_page_iter_next(struct sg_page_iter *piter);
 void __sg_page_iter_start(struct sg_page_iter *piter,
 			  struct scatterlist *sglist, unsigned int nents,
 			  unsigned long pgoffset);
 /**
  * sg_page_iter_page - get the current page held by the page iterator
  * @piter:	page iterator holding the page
  */
 static inline struct page *sg_page_iter_page(struct sg_page_iter *piter)
 {
 	return nth_page(sg_page(piter->sg), piter->sg_pgoffset);
 }

 /**
  * sg_page_iter_dma_address - get the dma address of the current page held by
  * the page iterator.
  * @piter:	page iterator holding the page
  */
 static inline dma_addr_t sg_page_iter_dma_address(struct sg_page_iter *piter)
 {
 	return sg_dma_address(piter->sg) + (piter->sg_pgoffset << PAGE_SHIFT);
 }

 /**
  * for_each_sg_page - iterate over the pages of the given sg list
  * @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
  */
 #define for_each_sg_page(sglist, piter, nents, pgoffset)		   \
 	for (__sg_page_iter_start((piter), (sglist), (nents), (pgoffset)); \
 	     __sg_page_iter_next(piter);)

 /*
  * Mapping sg iterator
  *
  * Iterates over sg entries mapping page-by-page.  On each successful
  * iteration, @miter->page points to the mapped page and
  * @miter->length bytes of data can be accessed at @miter->addr.  As
  * long as an interation is enclosed between start and stop, the user
  * is free to choose control structure and when to stop.
  *
  * @miter->consumed is set to @miter->length on each iteration.  It
  * can be adjusted if the user can't consume all the bytes in one go.
  * Also, a stopped iteration can be resumed by calling next on it.
  * This is useful when iteration needs to release all resources and
  * continue later (e.g. at the next interrupt).
  */

 #define SG_MITER_ATOMIC		(1 << 0)	 /* use kmap_atomic */
 #define SG_MITER_TO_SG		(1 << 1)	/* flush back to phys on unmap */
 #define SG_MITER_FROM_SG	(1 << 2)	/* nop */

 struct sg_mapping_iter {
 	/* the following three fields can be accessed directly */
 	struct page		*page;		/* currently mapped page */
 	void			*addr;		/* pointer to the mapped area */
 	size_t			length;		/* length of the mapped area */
 	size_t			consumed;	/* number of consumed bytes */
 	struct sg_page_iter	piter;		/* page iterator */

 	/* these are internal states, keep away */
 	unsigned int		__offset;	/* offset within page */
 	unsigned int		__remaining;	/* remaining bytes on page */
 	unsigned int		__flags;
 };

 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 		    unsigned int nents, unsigned int flags);
 bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset);
 bool sg_miter_next(struct sg_mapping_iter *miter);
 void sg_miter_stop(struct sg_mapping_iter *miter);

 #endif /* _LINUX_SCATTERLIST_H */
	#ifndef _LINUX_SCATTERLIST_H
	#define _LINUX_SCATTERLIST_H

	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/bug.h>
	#include <linux/mm.h>
	#include <asm/io.h>

	struct scatterlist {
	#ifdef CONFIG_DEBUG_SG
	unsigned long sg_magic;
	#endif
	unsigned long page_link;
	unsigned int offset;
	unsigned int length;
	dma_addr_t dma_address;
	#ifdef CONFIG_NEED_SG_DMA_LENGTH
	unsigned int dma_length;
	#endif
	};

	/*
	* These macros should be used after a dma_map_sg call has been done
	* to get bus addresses of each of the SG entries and their lengths.
	* You should only work with the number of sg entries dma_map_sg
	* returns, or alternatively stop on the first sg_dma_len(sg) which
	* is 0.
	*/
	#define sg_dma_address(sg) ((sg)->dma_address)

	#ifdef CONFIG_NEED_SG_DMA_LENGTH
	#define sg_dma_len(sg) ((sg)->dma_length)
	#else
	#define sg_dma_len(sg) ((sg)->length)
	#endif

	struct sg_table {
	struct scatterlist sgl; / the list */
	unsigned int nents; /* number of mapped entries */
	unsigned int orig_nents; /* original size of list */
	};

	/*
	* Notes on SG table design.
	*
	* We use the unsigned long page_link field in the scatterlist struct to place
	* the page pointer AND encode information about the sg table as well. The two
	* lower bits are reserved for this information.
	*
	* If bit 0 is set, then the page_link contains a pointer to the next sg
	* table list. Otherwise the next entry is at sg + 1.
	*
	* If bit 1 is set, then this sg entry is the last element in a list.
	*
	* See sg_next().
	*
	*/

	#define SG_MAGIC 0x87654321

	/*
	* 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) ((sg)->page_link & 0x01)
	#define sg_is_last(sg) ((sg)->page_link & 0x02)
	#define sg_chain_ptr(sg) \
	((struct scatterlist *) ((sg)->page_link & ~0x03))

	/**
	* sg_assign_page - Assign a given page to an SG entry
	* @sg: SG entry
	* @page: The page
	*
	* Description:
	* Assign page to sg entry. Also see sg_set_page(), the most commonly used
	* variant.
	*
	**/
	static inline void sg_assign_page(struct scatterlist sg, struct page page)
	{
	unsigned long page_link = sg->page_link & 0x3;

	/*
	* In order for the low bit stealing approach to work, pages
	* must be aligned at a 32-bit boundary as a minimum.
	*/
	BUG_ON((unsigned long) page & 0x03);
	#ifdef CONFIG_DEBUG_SG
	BUG_ON(sg->sg_magic != SG_MAGIC);
	BUG_ON(sg_is_chain(sg));
	#endif
	sg->page_link = page_link \| (unsigned long) page;
	}

	/**
	* sg_set_page - Set sg entry to point at given page
	* @sg: SG entry
	* @page: The page
	* @len: Length of data
	* @offset: Offset into page
	*
	* Description:
	* Use this function to set an sg entry pointing at a page, never assign
	* the page directly. We encode sg table information in the lower bits
	* of the page pointer. See sg_page() for looking up the page belonging
	* to an sg entry.
	*
	**/
	static inline void sg_set_page(struct scatterlist sg, struct page page,
	unsigned int len, unsigned int offset)
	{
	sg_assign_page(sg, page);
	sg->offset = offset;
	sg->length = len;
	}

	static inline struct page sg_page(struct scatterlist sg)
	{
	#ifdef CONFIG_DEBUG_SG
	BUG_ON(sg->sg_magic != SG_MAGIC);
	BUG_ON(sg_is_chain(sg));
	#endif
	return (struct page *)((sg)->page_link & ~0x3);
	}

	/**
	* sg_set_buf - Set sg entry to point at given data
	* @sg: SG entry
	* @buf: Data
	* @buflen: Data length
	*
	**/
	static inline void sg_set_buf(struct scatterlist sg, const void buf,
	unsigned int buflen)
	{
	#ifdef CONFIG_DEBUG_SG
	BUG_ON(!virt_addr_valid(buf));
	#endif
	sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
	}

	/*
	* Loop over each sg element, following the pointer to a new list if necessary
	*/
	#define for_each_sg(sglist, sg, nr, __i) \
	for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))

	/**
	* sg_chain - Chain two sglists together
	* @prv: First scatterlist
	* @prv_nents: Number of entries in prv
	* @sgl: Second scatterlist
	*
	* Description:
	* 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)
	{
	/*
	* offset and length are unused for chain entry. Clear them.
	*/
	prv[prv_nents - 1].offset = 0;
	prv[prv_nents - 1].length = 0;

	/*
	* Set lowest bit to indicate a link pointer, and make sure to clear
	* the termination bit if it happens to be set.
	*/
	prv[prv_nents - 1].page_link = ((unsigned long) sgl \| 0x01) & ~0x02;
	}

	/**
	* sg_mark_end - Mark the end of the scatterlist
	* @sg: SG entryScatterlist
	*
	* Description:
	* Marks the passed in sg entry as the termination point for the sg
	* table. A call to sg_next() on this entry will return NULL.
	*
	**/
	static inline void sg_mark_end(struct scatterlist *sg)
	{
	#ifdef CONFIG_DEBUG_SG
	BUG_ON(sg->sg_magic != SG_MAGIC);
	#endif
	/*
	* Set termination bit, clear potential chain bit
	*/
	sg->page_link \|= 0x02;
	sg->page_link &= ~0x01;
	}

	/**
	* sg_unmark_end - Undo setting the end of the scatterlist
	* @sg: SG entryScatterlist
	*
	* Description:
	* Removes the termination marker from the given entry of the scatterlist.
	*
	**/
	static inline void sg_unmark_end(struct scatterlist *sg)
	{
	#ifdef CONFIG_DEBUG_SG
	BUG_ON(sg->sg_magic != SG_MAGIC);
	#endif
	sg->page_link &= ~0x02;
	}

	/**
	* sg_phys - Return physical address of an sg entry
	* @sg: SG entry
	*
	* Description:
	* This calls page_to_phys() on the page in this sg entry, and adds the
	* sg offset. The caller must know that it is legal to call page_to_phys()
	* on the sg page.
	*
	**/
	static inline dma_addr_t sg_phys(struct scatterlist *sg)
	{
	return page_to_phys(sg_page(sg)) + sg->offset;
	}

	/**
	* sg_virt - Return virtual address of an sg entry
	* @sg: SG entry
	*
	* Description:
	* This calls page_address() on the page in this sg entry, and adds the
	* sg offset. The caller must know that the sg page has a valid virtual
	* mapping.
	*
	**/
	static inline void sg_virt(struct scatterlist sg)
	{
	return page_address(sg_page(sg)) + sg->offset;
	}

	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);
	void sg_init_one(struct scatterlist , const void , unsigned int);
	int sg_split(struct scatterlist *in, const int in_mapped_nents,
	const off_t skip, const int nb_splits,
	const size_t *split_sizes,
	struct scatterlist *out, int out_mapped_nents,
	gfp_t gfp_mask);

	typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
	typedef void (sg_free_fn)(struct scatterlist *, unsigned int);

	void __sg_free_table(struct sg_table , unsigned int, bool, sg_free_fn );
	void sg_free_table(struct sg_table *);
	int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int,
	struct scatterlist , gfp_t, sg_alloc_fn );
	int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
	int sg_alloc_table_from_pages(struct sg_table *sgt,
	struct page **pages, unsigned int n_pages,
	unsigned long offset, unsigned long size,
	gfp_t gfp_mask);

	size_t sg_copy_buffer(struct scatterlist sgl, unsigned int nents, void buf,
	size_t buflen, off_t skip, bool to_buffer);

	size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
	const void *buf, size_t buflen);
	size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
	void *buf, size_t buflen);

	size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
	const void *buf, size_t buflen, off_t skip);
	size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
	void *buf, size_t buflen, off_t skip);
	size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
	size_t buflen, off_t skip);

	/*
	* Maximum number of entries that will be allocated in one piece, if
	* a list larger than this is required then chaining will be utilized.
	*/
	#define SG_MAX_SINGLE_ALLOC (PAGE_SIZE / sizeof(struct scatterlist))

	/*
	* The maximum number of SG segments that we will put inside a
	* scatterlist (unless chaining is used). Should ideally fit inside a
	* single page, to avoid a higher order allocation. We could define this
	* to SG_MAX_SINGLE_ALLOC to pack correctly at the highest order. The
	* minimum value is 32
	*/
	#define SG_CHUNK_SIZE 128

	/*
	* Like SG_CHUNK_SIZE, but for archs that have sg chaining. This limit
	* is totally arbitrary, a setting of 2048 will get you at least 8mb ios.
	*/
	#ifdef CONFIG_ARCH_HAS_SG_CHAIN
	#define SG_MAX_SEGMENTS 2048
	#else
	#define SG_MAX_SEGMENTS SG_CHUNK_SIZE
	#endif

	#ifdef CONFIG_SG_POOL
	void sg_free_table_chained(struct sg_table *table, bool first_chunk);
	int sg_alloc_table_chained(struct sg_table *table, int nents,
	struct scatterlist *first_chunk);
	#endif

	/*
	* 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.
	*/
	struct sg_page_iter {
	struct scatterlist sg; / sg holding the page */
	unsigned int sg_pgoffset; /* page offset within the sg */

	/* these are internal states, keep away */
	unsigned int __nents; /* remaining sg entries */
	int __pg_advance; /* nr pages to advance at the
	* next step */
	};

	bool __sg_page_iter_next(struct sg_page_iter *piter);
	void __sg_page_iter_start(struct sg_page_iter *piter,
	struct scatterlist *sglist, unsigned int nents,
	unsigned long pgoffset);
	/**
	* sg_page_iter_page - get the current page held by the page iterator
	* @piter: page iterator holding the page
	*/
	static inline struct page sg_page_iter_page(struct sg_page_iter piter)
	{
	return nth_page(sg_page(piter->sg), piter->sg_pgoffset);
	}

	/**
	* sg_page_iter_dma_address - get the dma address of the current page held by
	* the page iterator.
	* @piter: page iterator holding the page
	*/
	static inline dma_addr_t sg_page_iter_dma_address(struct sg_page_iter *piter)
	{
	return sg_dma_address(piter->sg) + (piter->sg_pgoffset << PAGE_SHIFT);
	}

	/**
	* for_each_sg_page - iterate over the pages of the given sg list
	* @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
	*/
	#define for_each_sg_page(sglist, piter, nents, pgoffset) \
	for (__sg_page_iter_start((piter), (sglist), (nents), (pgoffset)); \
	__sg_page_iter_next(piter);)

	/*
	* Mapping sg iterator
	*
	* Iterates over sg entries mapping page-by-page. On each successful
	* iteration, @miter->page points to the mapped page and
	* @miter->length bytes of data can be accessed at @miter->addr. As
	* long as an interation is enclosed between start and stop, the user
	* is free to choose control structure and when to stop.
	*
	* @miter->consumed is set to @miter->length on each iteration. It
	* can be adjusted if the user can't consume all the bytes in one go.
	* Also, a stopped iteration can be resumed by calling next on it.
	* This is useful when iteration needs to release all resources and
	* continue later (e.g. at the next interrupt).
	*/

	#define SG_MITER_ATOMIC (1 << 0) /* use kmap_atomic */
	#define SG_MITER_TO_SG (1 << 1) /* flush back to phys on unmap */
	#define SG_MITER_FROM_SG (1 << 2) /* nop */

	struct sg_mapping_iter {
	/* the following three fields can be accessed directly */
	struct page page; / currently mapped page */
	void addr; / pointer to the mapped area */
	size_t length; /* length of the mapped area */
	size_t consumed; /* number of consumed bytes */
	struct sg_page_iter piter; /* page iterator */

	/* these are internal states, keep away */
	unsigned int __offset; /* offset within page */
	unsigned int __remaining; /* remaining bytes on page */
	unsigned int __flags;
	};

	void sg_miter_start(struct sg_mapping_iter miter, struct scatterlist sgl,
	unsigned int nents, unsigned int flags);
	bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset);
	bool sg_miter_next(struct sg_mapping_iter *miter);
	void sg_miter_stop(struct sg_mapping_iter *miter);

	#endif /* _LINUX_SCATTERLIST_H */