On Tue, Sep 06, 2016 at 12:15:15PM -0700, Darrick J. Wong wrote:

So far I've put the reflink flag to use in xfs_scrub to look for
obvious signs of brokenness such as extents that overlap or have the
shared flag set but the inode flag is off; and to skip various kinds
of checks that don't have to happen when blocks don't overlap.

I doubt there's much of a use for the flag outside of the XFS utilities.
For a while I pondered only exposing the fsxattr flag if the caller had
CAP_SYS_ADMIN (the level of priviledge required to run scrub) but
decided that I wouldn't change the existing interface like that unless
I had a really good reason.

I don't think CAP_SYS_ADMIN is nessecarily the right thing, but it's
still an XFS implementation detail which I don't think we should
pollute a flags API for normal user space applications with.