linux-kernel - Re: [PATCH 1/3] lib/scatterlist: introduce sg_pcopy_from_buffer() and sg_pcopy_to

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Date:	Thu, 6 Jun 2013 14:00:41 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Imre Deak <imre.deak@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	linux-crypto@...r.kernel.org,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	Douglas Gilbert <dgilbert@...erlog.com>,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/3] lib/scatterlist: introduce sg_pcopy_from_buffer()
 and sg_pcopy_to_buffer()

Hello,

On Thu, Jun 06, 2013 at 09:52:56PM +0900, Akinobu Mita wrote:
> +static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
> +{
> +	if (!miter->__remaining) {
> +		struct scatterlist *sg;
> +		unsigned long pgoffset;
> +
> +		if (!__sg_page_iter_next(&miter->piter))
> +			return false;
> +
> +		sg = miter->piter.sg;
> +		pgoffset = miter->piter.sg_pgoffset;
> +
> +		miter->__offset = pgoffset ? 0 : sg->offset;
> +		miter->__remaining = sg->offset + sg->length -
> +				(pgoffset << PAGE_SHIFT) - miter->__offset;
> +		miter->__remaining = min_t(unsigned long, miter->__remaining,
> +					   PAGE_SIZE - miter->__offset);
> +	}
> +
> +	return true;
> +}

It'd be better if separating out this function is a separate patch.
Mixing factoring out something and adding new stuff makes the patch a
bit harder to read.

> +static bool sg_miter_seek(struct sg_mapping_iter *miter, off_t offset)
> +{
> +	WARN_ON(miter->addr);
> +
> +	while (offset) {
> +		off_t consumed;
> +
> +		if (!sg_miter_get_next_page(miter))
> +			return false;
> +
> +		consumed = min_t(off_t, offset, miter->__remaining);
> +		miter->__offset += consumed;
> +		miter->__remaining -= consumed;
> +		offset -= consumed;
> +	}
> +
> +	return true;
> +}

While I think the above should work at the beginning, what if @miter
is in the middle of iteration and __remaining isn't zero?

Looks good to me otherwise.

Thanks.

-- 
tejun
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