linux-kernel - Re: [PATCH 2/13] Add sg helpers for iterating over a scatterlist table

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Date:	Thu, 10 May 2007 03:39:56 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/13] Add sg helpers for iterating over a scatterlist
 table

On Thu, 10 May 2007 12:21:44 +0200 Jens Axboe <jens.axboe@...cle.com> wrote:

> First step to being able to change the scatterlist setup without
> having to modify drivers (a lot :-)
> 
> Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> ---
>  include/linux/scatterlist.h |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index 4efbd9c..c5bffde 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -20,4 +20,13 @@ 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]))

Looks a bit underparenthesised.

> +/*
> + * Loop over each sg element, following the pointer to a new list if necessary
> + */
> +#define for_each_sg(sglist, sg, nr, __i)	\
> +	for (__i = 0, sg = (sglist); __i < nr; __i++, sg = sg_next(sg))
> +

So does this.

I don't see how it "follows the pointer to a new list".  All it's doing is
iterating across an array?

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