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

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Message-ID: <20150610184616.GL2729@linux.intel.com>
Date:	Wed, 10 Jun 2015 14:46:16 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Dan Williams <dan.j.williams@...el.com>, axboe@...nel.dk,
	sfr@...b.auug.org.au, rafael@...nel.org, neilb@...e.de,
	gregkh@...uxfoundation.org, linux-nvdimm@...ts.01.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-api@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...nel.org
Subject: Re: [PATCH v5 17/21] libnvdimm: infrastructure for btt devices

On Tue, Jun 09, 2015 at 08:42:00AM +0200, Christoph Hellwig wrote:
> > 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.

Don't screw up rw_page.  The point of rw_page is to read or write a page
cache page.  It can sleep, and it indicates success by using the page
flags.  Don't try and scqueeze rw_bytes into it.  If you want rw_bytes
to be a queue operation, that's one thing, but don't mess with rw_page.
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