On Wed, Aug 26, 2015 at 03:00:57PM +0200, David Sterba wrote:

quoted

I thought it breaks ABI if we choose a different value for the type
field of the ioctl. Am I misunderstanding it?

The ioctl is now private to btrfs, you're going to define the new ABI so
it IMHO should use the generic filesystem ioctl magic/namespace.

No, that's completly backwards.  We move up ioctls that have prooven
to be generally useful to common code, and we've done that with various
extN and XFS ones already.