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

[Matthew Wilcox]

From: Dan Williams [mailto:dan.j.williams@xxxxxxxxx]
> A couple weeks back, in the course of reviewing the memcpy_nocache()
> proposal from Brian, Linus subtly suggested that the pmem specific
> memcpy_to_pmem() routine be moved to be implemented at the driver
> level [1]:

Of course, there may not be a backing device either!  That will depend on the filesystem.
I see two possible routes here:

1. Add a new address_space_operation:

	const struct dax_operations *(*get_dax_ops)(struct address_space *);

2. Add two of the dax_operations to address_space_operations:

	size_t (*copy_from_iter)(struct address_space *, void *, size_t, struct iov_iter *);
	void (*flush)(struct address_space *, void *, size_t);
(we won't need ->direct_access as an address_space op because that'll be handled a different way in the brave new world that supports non-bdev-based filesystems)

Obviously in either case we'd have generic bdev versions for ext4, xfs and other block based filesystems, but filesystems with a character device or a network protocol behind them would do whatever it is they need to do.

I kind of prefer the second option, but does anyone else have a preference?