copy offload for SMB?

Christopher R. Hertel crh at
Fri Feb 22 09:22:50 MST 2013

On 02/22/2013 09:08 AM, David Disseldorp wrote:
> Server support is there, with a few quirks[1]. I'm not aware of anything
> pre-2k12 that uses it on the client side, but the ioctl itself has been
> around for donkey's years (SMB1), so there's likely something obscure
> using it.


IOCTL handling in SMB1 is flaky at best.  I believe that the
NT_TRANSACT_IOCTL call works, but SMB_COM_IOCTL is hamstrung and
TRANS2_IOCTL2 was never implemented.  Do you have pointers to docs showing
when this IOCTL was introduced to Windows and/or how it was used?

The OS/2 LAN Manager SMB dialect (and all subsequent SMB/CIFS dialects)
supported the SMB_COM_COPY and SMB_COM_MOVE SMB commands.  These commands
were supposed to use server-side operations to (respectively) copy and
rename files.  The implementations of those two commands in Windows NT and
anything beyond Windows NT is quite broken.  The commands are there, they
just don't work.

Chris -)-----

"Implementing CIFS - the Common Internet FileSystem" ISBN: 013047116X
Samba Team --     -)-----   Christopher R. Hertel
jCIFS Team --   -)-----   ubiqx development, uninq.
ubiqx Team --     -)-----   crh at
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