linux-kernel - RE: [[PATCH v1] 16/37] [CIFS] SMBD: Post a SMBD message with no payload

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Date:   Mon, 14 Aug 2017 23:12:31 +0000
From:   Tom Talpey <ttalpey@...rosoft.com>
To:     Long Li <longli@...rosoft.com>,
        Christoph Hellwig <hch@...radead.org>
CC:     Steve French <sfrench@...ba.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [[PATCH v1] 16/37] [CIFS] SMBD: Post a SMBD message with no
 payload

> -----Original Message-----
> From: Long Li
> Sent: Monday, August 14, 2017 6:51 PM
> To: Tom Talpey <ttalpey@...rosoft.com>; Christoph Hellwig
> <hch@...radead.org>
> Cc: Steve French <sfrench@...ba.org>; linux-cifs@...r.kernel.org; samba-
> technical@...ts.samba.org; linux-kernel@...r.kernel.org
> Subject: RE: [[PATCH v1] 16/37] [CIFS] SMBD: Post a SMBD message with no
> payload
> 
> 
> 
> > -----Original Message-----
> > From: Tom Talpey
> > Sent: Monday, August 14, 2017 12:00 PM
> > To: Long Li <longli@...rosoft.com>; Christoph Hellwig <hch@...radead.org>
> > Cc: Steve French <sfrench@...ba.org>; linux-cifs@...r.kernel.org; samba-
> > technical@...ts.samba.org; linux-kernel@...r.kernel.org
> > Subject: RE: [[PATCH v1] 16/37] [CIFS] SMBD: Post a SMBD message with no
> > payload
> >
> > > -----Original Message-----
> > > From: linux-cifs-owner@...r.kernel.org [mailto:linux-cifs-
> > > owner@...r.kernel.org] On Behalf Of Long Li
> > > Sent: Monday, August 14, 2017 2:20 PM
> > > To: Christoph Hellwig <hch@...radead.org>
> > > Cc: Steve French <sfrench@...ba.org>; linux-cifs@...r.kernel.org;
> > > samba- technical@...ts.samba.org; linux-kernel@...r.kernel.org
> > > Subject: RE: [[PATCH v1] 16/37] [CIFS] SMBD: Post a SMBD message with
> > > no payload
> > >
> > > > > Implement the function to send a SMBD message with no payload.
> > > > > This is
> > > > required at times when we want to extend credtis to server to have
> > > > it continue to send data, without sending any actual data payload.
> > > >
> > > > Shouldn't this just be implemented as a special case in the version
> > > > that posts data?
> > >
> > > It uses a different packet format "struct smbd_data_transfer_no_data".
> > > I can restructure some common code to share between packet sending
> > functions.
> >
> > The SMB Direct keepalive is just a Data Transfer Message with no payload
> > (MS-SMBD section 2.2.3) and the SMB_DIRECT_RESPONSE_REQUESTED flag
> > possibly set.  I don't see any need to define a special structure to describe
> > this?
> 
> Data Transfer Message has the following extra fields at the end of an empty
> packet.
> 
>         __le32 padding;

No need to omit the padding, it's ignored anyway and the DataLength is zero
so there's no other payload to consume. You can send a packet of pretty much
any length. Just send the regular struct.

BTW, the "padding" field is defined as variable array of bytes, meaning semantically
you might want to code it as u8 padding[0] as well. However in practice it is
either 4 bytes or not present at all, so you'd probably end up writing extra code
for that choice.

>         char buffer[0];
> 
> I agree with you those can be merged to a special structure case. Will make the
> change.

Tom.