[cifs-protocol] FSCTL_DUPLICATE_EXTENTS_TO_FILE questions

[David Disseldorp]

Dear Dochelp,

I've been testing FSCTL_DUPLICATE_EXTENTS_TO_FILE functionality against
a Windows Server 2016 server, and have noticed the following behaviour
which appears contrary to the [MS-FSCC] spec:

-------
2.3.8 FSCTL_DUPLICATE_EXTENTS_TO_FILE Reply
...
Error Code == STATUS_NOT_SUPPORTED
a) Target file is sparse, while source is a non-sparse file.
b) The source range is beyond the source file's allocation size.
   The destination range extends beyond the target file's allocation size.
   The caller might need to increase the target's allocation size before
   using FSCTL_DUPLICATE_EXTENTS_TO_FILE.
-------

(a) appears to be reversed, in that STATUS_NOT_SUPPORTED is returned if
the source is sparse, while the target is non-sparse. However, if target
is sparse while the source is non-sparse, then
FSCTL_DUPLICATE_EXTENTS_TO_FILE completes successfully.
(b) appears incorrect - issuing a FSCTL_DUPLICATE_EXTENTS_TO_FILE
request where the destination range extends beyond the target's
allocation/file size (zero) results in a successful response. However,
the file size remains zero in this case.

One final query - are there any lock conditions where
FSCTL_DUPLICATE_EXTENTS_TO_FILE will return STATUS_FILE_LOCK_CONFLICT?
As is, FSCTL_DUPLICATE_EXTENTS_TO_FILE appears to completely bypass file
locks.

Regards, David