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

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Message-ID: <x49twu6nugs.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 17 Jun 2015 12:57:39 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Christoph Hellwig <hch@....de>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Jens Axboe <axboe@...nel.dk>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Neil Brown <neilb@...e.de>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v5 17/21] libnvdimm: infrastructure for btt devices

Dan Williams <dan.j.williams@...el.com> writes:

> On Wed, Jun 17, 2015 at 9:47 AM, Jeff Moyer <jmoyer@...hat.com> wrote:
>> 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?
>
> ? in v6 ->rw_bytes() moved from libnvdimm local hackery to a top-level
> block device operation.  Is that your concern or something else?

Hmm, I guess I was conflating two things.  I see now that you did move
the rw_bytes into the block device operations, that looks good.  I'll
table my concerns over yet another stacking model until I can say
something intelligent about it.

Cheers,
Jeff
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