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

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Message-ID: <x49381qp9ic.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 17 Jun 2015 12:47:23 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Christoph Hellwig <hch@....de>,
	Dan Williams <dan.j.williams@...el.com>
Cc:	Matthew Wilcox <willy@...ux.intel.com>, axboe@...nel.dk,
	sfr@...b.auug.org.au, akpm@...ux-foundation.org, rafael@...nel.org,
	neilb@...e.de, gregkh@...uxfoundation.org,
	linux-nvdimm@...1.01.org, linux-kernel@...r.kernel.org,
	mingo@...nel.org, linux-acpi@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v5 17/21] libnvdimm: infrastructure for btt devices

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

> On Wed, Jun 10, 2015 at 02:46:16PM -0400, Matthew Wilcox wrote:
>> 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.
>
> Oh, I forgot about the page manipulating nature.  Yes, we'll need a different
> operation in this case.

I didn't see this addressed in the new patch set.  I'm also concerned
about the layering, but I haven't put enough time into it to really make
a better suggestion.  I really dislike the idea of yet another device
stacking model in the kernel and I'm worried the code will go in, and the
sysfs interface will end up as a "user abi" and we won't be able to
change it in the future.

Dan, have you made any progress on this, or do you have plans to?

Cheers,
Jeff
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