70eb8040dc
The core of the patch - allow the last sg element in a scatterlist table to point to the start of a new table. We overload the LSB of the page pointer to indicate whether this is a valid sg entry, or merely a link to the next list. Includes a fix from Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> correcting the ifdef ARCH_HAS_SG_CHAIN guarding sg_last(). Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
107 lines
2.7 KiB
C
107 lines
2.7 KiB
C
#ifndef _LINUX_SCATTERLIST_H
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#define _LINUX_SCATTERLIST_H
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#include <asm/scatterlist.h>
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#include <linux/mm.h>
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#include <linux/string.h>
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static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
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unsigned int buflen)
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{
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sg->page = virt_to_page(buf);
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sg->offset = offset_in_page(buf);
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sg->length = buflen;
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}
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static inline void sg_init_one(struct scatterlist *sg, const void *buf,
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unsigned int buflen)
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{
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memset(sg, 0, sizeof(*sg));
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sg_set_buf(sg, buf, buflen);
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}
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/*
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* We overload the LSB of the page pointer to indicate whether it's
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* a valid sg entry, or whether it points to the start of a new scatterlist.
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* Those low bits are there for everyone! (thanks mason :-)
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*/
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#define sg_is_chain(sg) ((unsigned long) (sg)->page & 0x01)
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#define sg_chain_ptr(sg) \
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((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01))
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/**
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* sg_next - return the next scatterlist entry in a list
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* @sg: The current sg entry
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*
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* Usually the next entry will be @sg@ + 1, but if this sg element is part
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* of a chained scatterlist, it could jump to the start of a new
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* scatterlist array.
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*
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* Note that the caller must ensure that there are further entries after
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* the current entry, this function will NOT return NULL for an end-of-list.
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*
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*/
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static inline struct scatterlist *sg_next(struct scatterlist *sg)
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{
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sg++;
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if (unlikely(sg_is_chain(sg)))
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sg = sg_chain_ptr(sg);
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return sg;
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}
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/*
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* Loop over each sg element, following the pointer to a new list if necessary
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*/
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#define for_each_sg(sglist, sg, nr, __i) \
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for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
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/**
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* sg_last - return the last scatterlist entry in a list
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* @sgl: First entry in the scatterlist
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* @nents: Number of entries in the scatterlist
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*
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* Should only be used casually, it (currently) scan the entire list
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* to get the last entry.
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*
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* Note that the @sgl@ pointer passed in need not be the first one,
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* the important bit is that @nents@ denotes the number of entries that
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* exist from @sgl@.
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*
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*/
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static inline struct scatterlist *sg_last(struct scatterlist *sgl,
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unsigned int nents)
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{
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#ifndef ARCH_HAS_SG_CHAIN
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struct scatterlist *ret = &sgl[nents - 1];
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#else
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struct scatterlist *sg, *ret = NULL;
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int i;
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for_each_sg(sgl, sg, nents, i)
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ret = sg;
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#endif
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return ret;
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}
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/**
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* sg_chain - Chain two sglists together
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* @prv: First scatterlist
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* @prv_nents: Number of entries in prv
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* @sgl: Second scatterlist
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*
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* Links @prv@ and @sgl@ together, to form a longer scatterlist.
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*
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*/
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static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
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struct scatterlist *sgl)
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{
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#ifndef ARCH_HAS_SG_CHAIN
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BUG();
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#endif
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prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01);
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}
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#endif /* _LINUX_SCATTERLIST_H */
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