There's been a long-term disagreement about how the per-file DAX flag
should work.
* Should it exist at all?
* What happens when the DAX flag is cleared?
* Should it be not allowed and return an error?
(Or maybe only if the file is otherwise opened anywhere in the system?)
* Should it only takes effect when the file system is unmounted,
or when the inode drops out of the inode cache?
* Should we remove the flag entirely and make it be something the
system automagically infers?
I had hoped consensus would be achieved before the ext4 per-file DAX
flag lands, but it hasn't for a *long* time. Technically the DAX flag
is "experimental", which technically means it could be removed ---
although I suspect at this point, it would break some userspace, so
our options about how to adjust the semantics of the flag are probably
constrained.
- Ted
