New ioctl - FSCTL_DUPLICATE_EXTENTS_TO_FILE

[David Disseldorp]

On Tue, 27 Jan 2015 12:23:55 -0600, Steve French wrote:

> Has anyone tried the new ioctl (MS-FSCC) defined in the most recent
> update.  See section 2.3.7
> 
> Looks interesting for a new variant of copy offload
> 
> "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.
- It takes a regular file handle for the source, instead of requiring a
  preliminary SRV_REQUEST_RESUME_KEY exchange.
- Only a single chunk can be duplicated per request, rather than
  multiple.
- Overlapping ranges are not supported.
- The length field is 64-bits wide, instead of 32.
- The response only carries the status code. This may imply there is no
  server-advertised limit to the length of the request, further
  indicating that it's COW based.

Time to start poking around with smbtorture :)

Cheers, David