SG_CHAIN
(unsigned long)sgl | SG_CHAIN;
unsigned long page_link = sg->page_link & (SG_CHAIN | SG_END);
chain_sg->page_link = ((unsigned long) sgl | SG_CHAIN) & ~SG_END;
sg->page_link &= ~SG_CHAIN;
#define SG_PAGE_LINK_MASK (SG_CHAIN | SG_END)
return __sg_flags(sg) & SG_CHAIN;
#define sg_is_chain(sg) ((sg)->page_link & SG_CHAIN)
((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))