On Fri, Sep 25, 2015 at 1:48 PM, Anna Schumaker
[off-list ref] wrote:

The NFS server will need some kind offallback for filesystems that don't
have any kind of copy acceleration, and it should be generally useful to
have an in-kernel copy to avoid lots of switches between kernel and user
space.

I make this configurable by adding two new flags.  Users who only want a
reflink can pass COPY_FR_REFLINK, and users who want a full data copy can
pass COPY_FR_COPY.  The default (flags=0) means to first attempt a
reflink, but use the pagecache if that fails.

Can you clarify how the subject line fits in?  I'm a bit lost.

--Andy