Re: [PATCH 00/13] dax, pmem: move cpu cache maintenance to libnvdimm

[Dan Williams]

On Mon, Jan 23, 2017 at 8:00 AM, Christoph Hellwig <hch@xxxxxx> wrote:
> On Sun, Jan 22, 2017 at 11:10:04PM -0800, Dan Williams wrote:
>> How about we solve the copy_from_user() abuse first before we hijack
>> this thread for some future feature that afaics has no patches posted
>> yet.
>
> Solving copy_from_user abuse first sounds perfectly fine to me.  But
> please do so without abusing the block layer for persistent memory
> access.  Given that we don't have use cases for different pmem access
> methods in a single OS image yet let's avoid introducing new ops
> for now and just remove the copy_from_user abuse.

The use case that we have now is distinguishing volatile vs persistent
memory (brd vs pmem).

I took a look at mtd layering approach and the main difference is that
layers above the block layer do not appear to know anything about mtd
specifics. For fs/dax.c we currently need some path to retrieve a dax
anchor object through the block device.

> In the longer run I like your dax_operations, but they need to be
> separate from the block layer.

I'll move them from block_device_operations to dax data hanging off of
the bdev_inode, or is there a better way to go from bdev-to-dax?