[RFC] allow enabling reflinks at runtime

[Christoph Hellwig]

On Fri, Jun 03, 2016 at 08:54:15AM +1000, Dave Chinner wrote:
> On Thu, Jun 02, 2016 at 04:19:07PM +0200, Christoph Hellwig wrote:
> > I've had some vocal user requests to allow enabling reflinks at run time,
> > which happens to be a mostly trivial feature.  The only caveat is that we
> > need a large enough log size to support the reflink requirements, but for
> > typical large file systems that's not an issue.
> 
> Hmmm - how does this interact with all the rmap code? I was not
> planning on enabling reflink without rmap and vice versa simply
> because it makes the validation and testing matrix vastly more
> complex.

Uh.  So far I've only been testing pure reflink code, mostly because
rmap really doesn't buy much for the use case I'm working on.
Enabling rmap post-mkfs is defintively a different ballpark, and probably
not worth it even if it would be doable.