New ioctl - FSCTL_DUPLICATE_EXTENTS_TO_FILE

[Steve French]

On Mon, Feb 9, 2015 at 5:51 PM, David Disseldorp <ddiss at suse.de> wrote:
> On Wed, 28 Jan 2015 19:22:03 +0100, David Disseldorp wrote:
>
>> > "A new File System Control (FSCTL) has been added to support the new
>> > FSCTL_DUPLICATE_EXTENTS_TO_FILE operation in [MS-FSA]."
>>
>> I haven't played with it yet, but from the [MS-FCC] 20150119 preview
>> doc it looks very similar to copy-chunk, with a few small differences:
>> - It's only supported on ReFS, which may indicate that it's implemented
>>   using COW clones.
>
> The [MS-FSA] draft can be found at:
> http://download.microsoft.com/download/C/6/C/C6C3C6F1-E84A-44EF-82A9-49BD3AAD8F58/Windows/%5BMS-FSA-Diff%5D.pdf
>
> It pretty much confirms that it's COW based:
> "The purpose of this operation is to make it look like a copy of a
>  region from the source stream to the target stream has occurred when
>  in reality no data is actually copied. This operation modifies the
>  target stream’s extent list such that, the same clusters are pointed
>  to by both the source and target streams’ extent lists for the region
>  being copied."
>
> @Steve, it looks like the perfect candidate for cp --reflink mapping on
> the client side.

agreed.  I will take a look against Windows 10 current beta to see if
it accepts or rejects it.


-- 
Thanks,

Steve