linux-kernel - Re: [PATCH] block: fix blk_queue_alignment

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Message-ID: <yq1ab30jdtg.fsf@sermon.lab.mkp.net>
Date:	Sun, 19 Jul 2009 22:19:55 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Christoph Hellwig <hch@....de>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: fix blk_queue_alignment_offset

>>>>> "hch" == Christoph Hellwig <hch@....de> writes:

hch> We need to mask out bits inside the logical block, not outside of
hch> it, otherwise we'll always get a 0 alignment_offset.

The alignment_offset only makes sense if physical_block_size >
logical_block_size.  For instance (63 * 512) & (4096 - 1) = 3584.

Your patch would yield 28672 = 4096 * 7 and that's incorrect; LBA 63 is
not aligned on a 4KB boundary...

-- 
Martin K. Petersen	Oracle Linux Engineering
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