Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs

[Christoph Hellwig]

On Wed, Sep 14, 2016 at 11:54:38PM -0700, Dan Williams wrote:
> The DAX property, page cache bypass, of a VMA is only detectable via the
> vma_is_dax() helper to check the S_DAX inode flag.  However, this is
> only available internal to the kernel and is a property that userspace
> applications would like to interrogate.

They have absolutely no business knowing such an implementation detail.