Re: [dpdk-dev] [PATCH] pmd: Add generic support for TCP TSO (Transmit Segmentation Offload)

["Walukiewicz, Miroslaw" <Miroslaw.Walukiewicz@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Monday, October 20, 2014 3:51 PM
> To: Walukiewicz, Miroslaw
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] pmd: Add generic support for TCP TSO
> (Transmit Segmentation Offload)
> 
> 2014-10-20 12:45, Walukiewicz, Miroslaw:
> > > >  	/* fields to support TX offloads */
> > > > -	union {
> > > > -		uint16_t l2_l3_len; /**< combined l2/l3 lengths as single var
> > > */
> > > > -		struct {
> > > > -			uint16_t l3_len:9;      /**< L3 (IP) Header Length. */
> > > > -			uint16_t l2_len:7;      /**< L2 (MAC) Header Length.
> > > */
> > > > +	/* two bytes - l2/l3 len for compatibility (endian issues)
> > > > +	 * two bytes - reseved for alignment
> > > > +	 * two bytes - l4 len (TCP/UDP) header len
> > > > +	 * two bytes - TCP tso segment size
> > > > + 	 */
> > > > +	struct {
> > > > +		union {
> > > > +			uint16_t l2_l3_len; /**< combined l2/l3 len */
> > > > +			struct {
> > > > +				uint16_t l3_len:9; /**< L3 (IP) Header */
> > > > +				uint16_t l2_len:7; /**< L2 (MAC) Header */
> > > > +			};
> > > >  		};
> > >
> > > Why nesting these fields in an anonymous structure?
> >
> > I want to keep a source compatibility with non-TSO applications using that
> > field for example IP checksum computing by NIC.
> > Keeping this structure anonymous I do not require changes in old
> > applications that do not need TSO support.
> >
> > The second argument is that in original patch extending the rte_mbuf to
> 128
> > bytes made by Bruce the author made this structure anonymous and I
> follow
> > this assumption too.
> 
> Excuse me, maybe I missed something, but I still don't understand why you
> are
> embedding the union into a struct?

You are right. It has no sense. 
Let me send a new version of the patch with new structure definition and better description

> 
> --
> Thomas