Date: Wed, 26 Aug 2015 06:07:12 -0700
From: Christoph Hellwig <hch@infradead.org>
To: dsterba@suse.cz, Peng Tao <tao.peng@primarydata.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Christoph Hellwig <hch@infradead.org>, Zach Brown <zab@zabbo.net>,
        Darren Hart <dvhart@linux.intel.com>,
        Bruce Fields <bfields@fieldses.org>,
        Jeff Layton <jeff.layton@primarydata.com>, linux-btrfs@vger.kernel.org,
        Devel FS Linux <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH RFC 02/11] vfs/btrfs: add .clone_range file operation
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On Wed, Aug 26, 2015 at 03:00:57PM +0200, David Sterba wrote:
> > 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.