Messages in this thread | | | Date | Thu, 10 May 2007 13:23:55 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH 7/13] i386 sg: add support for chaining scatterlists |
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On Thu, May 10 2007, Benny Halevy wrote: > Jens Axboe wrote: > > +#define sg_is_chain(sg) ((unsigned long) (sg)->page & 0x01) > > +#define sg_chain_ptr(sg) \ > > + ((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01)) > > + > > +/* > > + * We overload the meaning of ->page for sg chaining. If the LSB is > > + * set, the page member contains a pointer to the next sgtable. > > + */ > > +static inline struct scatterlist *sg_next(struct scatterlist *sg) > > +{ > > + if (sg_is_chain(sg)) > > + return sg_chain_ptr(sg); > > + > > + return sg + 1; > > +} > > Jens, should sg_next ever return the sg containing the chain link? > If sg points at the entry right before the link entry, don't we > want to skip it? > > E.g.: > > static inline struct scatterlist *sg_next(struct scatterlist *sg) > { > struct scatterlist *next; > > /* just in case, shouldn't really ever be here */ > if (sg_is_chain(sg)) > return sg_chain_ptr(sg); > > next = sg + 1; > > if (sg_is_chain(next)) > return sg_chain_ptr(next); > > return next; > }
You are right, I got that mixed up, I changed the setup to overloading ->page right before posting it. So:
static inline struct scatterlist *sg_next(struct scatterlist *sg) { sg++;
if (unlikely(sg_is_chain(sg))) sg = sg_chain_ptr(sg);
return sg; }
-- Jens Axboe
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