On Fri, Sep 08, 2017 at 12:20:28AM -0700, Christoph Hellwig wrote:

On Thu, Sep 07, 2017 at 03:08:31PM -0600, Ross Zwisler wrote:

quoted

Before support for the per-inode DAX flag was disabled the XFS the code had
an issue where the user couldn't reliably tell whether or not DAX was being
used to service page faults and I/O when the DAX mount option was used.  In
this case each inode within the mounted filesystem started with S_DAX set
due to the mount option, but it could be cleared if someone touched the
individual inode flag.

Looks good, but can you please add a testcase to xfstests for this?

Hmm...aside from looking at tracepoints, I'm not sure how to detect whether or
not S_DAX is actually being used for an inode.  I don't see any other xfstests
that try and look at the trace buffer, but I guess that could work.

Do you know of a better way to detect this test failure/success?

Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks for the review!