diff options
Diffstat (limited to 'include/linux/scatterlist.h')
| -rw-r--r-- | include/linux/scatterlist.h | 78 |
1 files changed, 54 insertions, 24 deletions
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 1645795cbb1..c6136e8a7f5 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -2,9 +2,26 @@ #define _LINUX_SCATTERLIST_H #include <asm/scatterlist.h> -#include <asm/io.h> #include <linux/mm.h> #include <linux/string.h> +#include <asm/io.h> + +/* + * Notes on SG table design. + * + * Architectures must provide an unsigned long page_link field in the + * scatterlist struct. We use that 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(). + * + */ /** * sg_set_page - Set sg entry to point at given page @@ -20,11 +37,20 @@ **/ static inline void sg_set_page(struct scatterlist *sg, struct page *page) { - sg->page = page; + unsigned long page_link = sg->page_link & 0x3; + + sg->page_link = page_link | (unsigned long) page; } -#define sg_page(sg) ((sg)->page) +#define sg_page(sg) ((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) { @@ -38,26 +64,27 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf, * 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) ((unsigned long) (sg)->page & 0x01) +#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 *) ((unsigned long) (sg)->page & ~0x01)) + ((struct scatterlist *) ((sg)->page_link & ~0x03)) /** * sg_next - return the next scatterlist entry in a list * @sg: The current sg entry * - * Usually the next entry will be @sg@ + 1, but if this sg element is part - * of a chained scatterlist, it could jump to the start of a new - * scatterlist array. - * - * Note that the caller must ensure that there are further entries after - * the current entry, this function will NOT return NULL for an end-of-list. + * Description: + * Usually the next entry will be @sg@ + 1, but if this sg element is part + * of a chained scatterlist, it could jump to the start of a new + * scatterlist array. * - */ + **/ static inline struct scatterlist *sg_next(struct scatterlist *sg) { - sg++; + if (sg_is_last(sg)) + return NULL; + sg++; if (unlikely(sg_is_chain(sg))) sg = sg_chain_ptr(sg); @@ -75,14 +102,15 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg) * @sgl: First entry in the scatterlist * @nents: Number of entries in the scatterlist * - * Should only be used casually, it (currently) scan the entire list - * to get the last entry. + * Description: + * Should only be used casually, it (currently) scan the entire list + * to get the last entry. * - * Note that the @sgl@ pointer passed in need not be the first one, - * the important bit is that @nents@ denotes the number of entries that - * exist from @sgl@. + * Note that the @sgl@ pointer passed in need not be the first one, + * the important bit is that @nents@ denotes the number of entries that + * exist from @sgl@. * - */ + **/ static inline struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents) { @@ -105,16 +133,17 @@ static inline struct scatterlist *sg_last(struct scatterlist *sgl, * @prv_nents: Number of entries in prv * @sgl: Second scatterlist * - * Links @prv@ and @sgl@ together, to form a longer 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) { #ifndef ARCH_HAS_SG_CHAIN BUG(); #endif - prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01); + prv[prv_nents - 1].page_link = (unsigned long) sgl | 0x01; } /** @@ -128,13 +157,14 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents, **/ static inline void sg_mark_end(struct scatterlist *sgl, unsigned int nents) { + sgl[nents - 1].page_link = 0x02; } static inline void __sg_mark_end(struct scatterlist *sg) { + sg->page_link |= 0x02; } - /** * sg_init_one - Initialize a single entry sg list * @sg: SG entry @@ -187,7 +217,7 @@ static inline unsigned long sg_phys(struct scatterlist *sg) /** * sg_virt - Return virtual address of an sg entry - * @sg: SG entry + * @sg: SG entry * * Description: * This calls page_address() on the page in this sg entry, and adds the |