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author | Jens Axboe <jens.axboe@oracle.com> | 2007-07-16 21:17:16 +0200 |
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committer | Jens Axboe <jens.axboe@oracle.com> | 2007-10-16 11:08:51 +0200 |
commit | 70eb8040dc81212c884a464b75e37dca8014f3ad (patch) | |
tree | 79d23b3ef2635032e6060dfa9b06e4f885a8cb10 /include/linux/scatterlist.h | |
parent | c6132da1704be252ee6c923f47501083d835c238 (diff) | |
download | linux-stable-70eb8040dc81212c884a464b75e37dca8014f3ad.tar.gz linux-stable-70eb8040dc81212c884a464b75e37dca8014f3ad.tar.bz2 linux-stable-70eb8040dc81212c884a464b75e37dca8014f3ad.zip |
Add chained sg support to linux/scatterlist.h
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>
Diffstat (limited to 'include/linux/scatterlist.h')
-rw-r--r-- | include/linux/scatterlist.h | 79 |
1 files changed, 77 insertions, 2 deletions
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index bed5ab4d756a..2dc7464cce52 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -20,8 +20,36 @@ static inline void sg_init_one(struct scatterlist *sg, const void *buf, sg_set_buf(sg, buf, buflen); } -#define sg_next(sg) ((sg) + 1) -#define sg_last(sg, nents) (&(sg[(nents) - 1])) +/* + * 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) ((unsigned long) (sg)->page & 0x01) +#define sg_chain_ptr(sg) \ + ((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01)) + +/** + * 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. + * + */ +static inline struct scatterlist *sg_next(struct scatterlist *sg) +{ + sg++; + + if (unlikely(sg_is_chain(sg))) + sg = sg_chain_ptr(sg); + + return sg; +} /* * Loop over each sg element, following the pointer to a new list if necessary @@ -29,4 +57,51 @@ static inline void sg_init_one(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)) +/** + * sg_last - return the last scatterlist entry in a list + * @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. + * + * 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) +{ +#ifndef ARCH_HAS_SG_CHAIN + struct scatterlist *ret = &sgl[nents - 1]; +#else + struct scatterlist *sg, *ret = NULL; + int i; + + for_each_sg(sgl, sg, nents, i) + ret = sg; + +#endif + return ret; +} + +/** + * sg_chain - Chain two sglists together + * @prv: First scatterlist + * @prv_nents: Number of entries in prv + * @sgl: Second scatterlist + * + * 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); +} + #endif /* _LINUX_SCATTERLIST_H */ |