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

[Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Wed, Jun 17, 2015 at 9:47 AM, Jeff Moyer <jmoyer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org> 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?