XFStests generic/080: mtime and ctime not updated for dax mmap access

[stevenjswanson]

mtime and ctime are not updated in response to mmap() updates.

It's clear that they should be updated. If not, then programs like make will fail if rules use mmap to modify files.

Interesting article discussing the issue of mtime/ctime on mmap files.

https://lwn.net/Articles/564120/

It's not quite clear if the approach described got upstreamed or not.