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    SubjectRe: [PATCH 7/13] i386 sg: add support for chaining scatterlists
    On Thu, May 10 2007, Andrew Morton wrote:
    > On Thu, 10 May 2007 12:46:53 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:
    >
    > > On Thu, May 10 2007, Jens Axboe wrote:
    > > > Yeah, I'm inclined to agree. Perhaps it would be better to put this
    > > > stuff in lib/scatterlist.c or something like that instead?
    > > >
    > > > > > +/*
    > > > > > + * 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
    > > > >
    > > > > Can use BUILD_BUG_ON here. Or just #error.
    > > >
    > > > Good idea, thanks!
    > >
    > > No wait a second, that wont work. The code is always being built in sg
    > > scsi_lib.c, it should just not be called unless we can do chaining. We
    > > will never have a large number of segments that require chaining without
    > > ARCH_HAS_SG_CHAIN, so it'll never be called in that case. So it has to
    > > remain as it is, a BUG().
    >
    > Confused. If it should never be called, why does it even get compiled in?

    I can hide it behind ARCH_HAS_SG_CHAIN and provide something ala

    #define sg_chain(prv, x, sgl) BUG()

    for when that is not defined. It still needs to be visible.

    --
    Jens Axboe

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