Add reflink copy over SMB3.11 with new FSCTL_DUPLICATE_EXTENTS

 Getting fantastic copy performance with cp --reflink over SMB3.11
 using the new FSCTL_DUPLICATE_EXTENTS.

 This FSCTL was added in the SMB3.11 dialect (testing was
 against REFS file system) so have put it as a 3.11 protocol
 specific operation ("vers=3.1.1" on the mount).  Tested at
 the SMB3 plugfest in Redmond.

 It depends on the new FS Attribute (BLOCK_REFCOUNTING) which
 is used to advertise support for the ability to do this ioctl
 (if you can support multiple files pointing to the same block
 than this refcounting ability or equivalent is needed to
 support the new reflink-like duplicate extent SMB3 ioctl.

Signed-off-by: Steve French <steve.french@primarydata.com>
diff --git a/fs/cifs/smbfsctl.h b/fs/cifs/smbfsctl.h
index 83efa59..d098da6 100644
--- a/fs/cifs/smbfsctl.h
+++ b/fs/cifs/smbfsctl.h
@@ -78,6 +78,7 @@
 #define FSCTL_QUERY_ALLOCATED_RANGES 0x000940CF /* BB add struct */
 #define FSCTL_SET_DEFECT_MANAGEMENT  0x00098134 /* BB add struct */
 #define FSCTL_FILE_LEVEL_TRIM        0x00098208 /* BB add struct */
+#define FSCTL_DUPLICATE_EXTENTS_TO_FILE 0x00098344
 #define FSCTL_SIS_LINK_FILES         0x0009C104
 #define FSCTL_PIPE_PEEK              0x0011400C /* BB add struct */
 #define FSCTL_PIPE_TRANSCEIVE        0x0011C017 /* BB add struct */