Messages in this thread | | | Date | Thu, 10 May 2007 18:30:19 +0530 | From | "Satyam Sharma" <> | Subject | Re: [PATCH 7/12] i386 sg: add support for chaining scatterlists |
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Hi Jens,
On 5/10/07, Jens Axboe <jens.axboe@oracle.com> wrote: > 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. > > Signed-off-by: Jens Axboe <jens.axboe@oracle.com> > --- > include/asm-i386/scatterlist.h | 2 + > include/linux/scatterlist.h | 52 ++++++++++++++++++++++++++++++++++++++- > 2 files changed, 52 insertions(+), 2 deletions(-) > > diff --git a/include/asm-i386/scatterlist.h b/include/asm-i386/scatterlist.h > index d7e45a8..bd5164a 100644 > --- a/include/asm-i386/scatterlist.h > +++ b/include/asm-i386/scatterlist.h > @@ -10,6 +10,8 @@ struct scatterlist { > unsigned int length; > }; > > +#define ARCH_HAS_SG_CHAIN > + > /* These macros should be used after a pci_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 pci_map_sg > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index bed5ab4..fa2dc1c 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > [...] > +/* > + * We could improve this by passing in the maximum size of an sglist, so > + * we could jump directly to the last table. That would eliminate this > + * (potentially) lengthy scan. > + */ > +static inline struct scatterlist *sg_last(struct scatterlist *sgl, > + unsigned int nents) > +{ > +#ifdef 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; > +} > + > +/* > + * Chain previous sglist to this one > + */ > +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 */
(Style triviality)
In include/linux/scatterlist.h, why not simply:
#ifdef ARCH_HAS_SG_CHAIN
> +/* > + * We could improve this by passing in the maximum size of an sglist, so > + * we could jump directly to the last table. That would eliminate this > + * (potentially) lengthy scan. > + */ > +static inline struct scatterlist *sg_last(struct scatterlist *sgl, > + unsigned int nents) > +{ > + struct scatterlist *ret = &sgl[nents - 1]; > + return ret; > +} > + > +/* > + * Chain previous sglist to this one > + */ > +static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents, > + struct scatterlist *sgl) > +{ > + prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01); > +}
#else
> +/* > + * We could improve this by passing in the maximum size of an sglist, so > + * we could jump directly to the last table. That would eliminate this > + * (potentially) lengthy scan. > + */ > +static inline struct scatterlist *sg_last(struct scatterlist *sgl, > + unsigned int nents) > +{ > + struct scatterlist *sg, *ret = NULL; > + int i; > + > + for_each_sg(sgl, sg, nents, i) > + ret = sg; > + > + return ret; > +} > + > +/* > + * Chain previous sglist to this one > + */ > +static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents, > + struct scatterlist *sgl) > +{ > + BUG(); > +}
#endif /* ARCH_HAS_SG_CHAIN */
Similar to most of the other headers I've seen, and avoids multiple usage if #ifdef / #ifndef. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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