Re: [PATCH 02/15] libnvdimm: infrastructure for btt devices

From: Dan Williams
Date: Tue Jun 23 2015 - 16:33:57 EST

On Tue, Jun 23, 2015 at 8:19 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> On Tue, Jun 23, 2015 at 3:19 AM, Christoph Hellwig <hch@xxxxxx> wrote:
>> On Mon, Jun 22, 2015 at 12:02:54PM -0700, Dan Williams wrote:
>>> I don't see the need to re-invent partitioning which is the path this
>>> requested rework is putting us on...
>>> However, when the need arises for smaller granularity BTT we can have
>>> the partition fight then. To be clear, I believe that need is already
>>> here today, but I'm not in a position to push that agenda at this late
>>> date.
>> Instead of all this complaining and moaning let's figure out what
>> architecture you'd actually want. The one I had in mind is:
>> +------------------------------+
>> | block layer (& partitions) |
>> +---------------+--------------+--------------------+
>> | pmem driver | btt driver | other consumers |
>> +---------------+--------------+--------------------+
>> | pmem API through libnvdimm |
>> +---------------------------------------------------+
> I've got this mostly coded up. The nice property is that BTTs now
> become another flavor of the same namespace.

This approach has grown on me since yesterday. I neglected to realize
that we can carve out a BLK-mode namespace to be a BTT enabled log
device if the need arises to satisfy what BTT on a partition was doing
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