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Date: Fri, 30 Nov 2012 11:09:20 -0500
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v2 1/3] xfs: use b_maps[] for discontiguous buffers
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	<20121128222622.688093599@sgi.com>
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To: Mark Tinguely <tinguely@sgi.com>
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>  use_alloc_page:
> -	start = BBTOB(bp->b_map.bm_bn) >> PAGE_SHIFT;
> -	end = (BBTOB(bp->b_map.bm_bn + bp->b_length) + PAGE_SIZE - 1)
> +	start = BBTOB(bp->b_maps[0].bm_bn) >> PAGE_SHIFT;
> +	end = (BBTOB(bp->b_maps[0].bm_bn + bp->b_length) + PAGE_SIZE - 1)

Btw, how is this logic supposed to work for discontiguous buffers?

Each of them might straddle boundaries individually, so doing the
start/end calculation for the number of pages isn't going to be correct.

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