linux-kernel - Re: [PATCH v5 17/21] libnvdimm: infrastructure for btt devices

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Message-ID: <20150609064200.GE9804@lst.de>
Date:	Tue, 9 Jun 2015 08:42:00 +0200
From:	Christoph Hellwig <hch@....de>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-nvdimm@...ts.01.org, axboe@...nel.dk, sfr@...b.auug.org.au,
	rafael@...nel.org, neilb@...e.de, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	linux-acpi@...r.kernel.org, jmoyer@...hat.com,
	linux-api@...r.kernel.org, akpm@...ux-foundation.org, hch@....de
Subject: Re: [PATCH v5 17/21] libnvdimm: infrastructure for btt devices

On Mon, Jun 01, 2015 at 08:15:41PM -0400, Dan Williams wrote:
> Block devices from an nd bus, in addition to accepting "struct bio"
> based requests, also have the capability to perform byte-aligned
> accesses.  By default only the bio/block interface is used.  However, if
> another driver can make effective use of the byte-aligned capability it
> can claim/disable the block interface and use the byte-aligned "nd_io"
> interface.
> 
> The BTT driver is the initial first consumer of this mechanism to allow
> layering atomic sector update guarantees on top of nd_io capable
> libnvdimm-block-devices, or their partitions.

As mentioned during the last time of the review the layering here
is complete broken.  If you expose additional capabilities from a block
device do it at the block device level.  That is enhance the rw_page
callback to allo byte sized access, add a capability flag on the queue,
etc.
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