<pre> FSCTLDUPLICATEEXTENTSTOFILE is a new SMB3 ioctl introduced with Windows Server 2016 (currently in technical preview), which allows for a client to remotely request that the server perform a COW clone of a specified file: https://msdn.microsoft.com/en-us/library/mt182620.aspx </pre>

<pre> The cifs.ko Linux kernel SMB client includes support for FSCTLDUPLICATEEXTENTSTOFILE, which is invoked for cp --reflink initiated COW clone operations. </pre>

<pre> Samba has existing support for COW clones atop Btrfs via FSCTLSRVCOPYCHUNK: https://wiki.samba.org/index.php/Server-Side_Copy </pre>

<pre> This functionality should be extended to support the new FSCTLDUPLICATEEXTENTSTOFILE ioctl, to allow for remote COW clone requests from new (Windows10+) clients, and the cifs.ko kernel client. </pre>

Time Plan:

• Install Windows Server 2016 Technical Preview
• Test cifs.ko fsctl support
• Implement Samba client/smbtorture functionality
• Implement Samba server support
• Plumb functionality into Btrfs backend, for remote COW clones
• Submit upstream