Re: [dpdk-dev] [PATCH v4 3/3] mbuf:replace the inner_l2_len and the inner_l3_len fields

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Didier

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of didier.pallard
> Sent: Tuesday, December 02, 2014 2:53 PM
> To: Liu, Jijiang; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v4 3/3] mbuf:replace the inner_l2_len and the inner_l3_len fields
> 
> Hello,
> 
> On 12/02/2014 07:52 AM, Jijiang Liu wrote:
> > Replace the inner_l2_len and the inner_l3_len field with the outer_l2_len and outer_l3_len field, and rework csum forward engine
> and i40e PMD due to  these changes.
> >
> > Signed-off-by: Jijiang Liu <jijiang.liu@intel.com>
> [...]
> > --- a/lib/librte_mbuf/rte_mbuf.h
> > +++ b/lib/librte_mbuf/rte_mbuf.h
> > @@ -276,8 +276,8 @@ struct rte_mbuf {
> >   			uint64_t tso_segsz:16; /**< TCP TSO segment size */
> >
> >   			/* fields for TX offloading of tunnels */
> > -			uint64_t inner_l3_len:9; /**< inner L3 (IP) Hdr Length. */
> > -			uint64_t inner_l2_len:7; /**< inner L2 (MAC) Hdr Length. */
> > +			uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr Length. */
> > +			uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr Length. */
> >
> >   			/* uint64_t unused:8; */
> >   		};
> 
> Sorry for entering lately this discussion, but i'm not convinced by the
> choice of outer_lx_len rather than inner_lx_len for new fields.
> I agree with Olivier that new flags should only be related to the use of
> new fields, to maintain coherency with oldest implementations.
> But from a stack point of view, i think it is better to have lx_len
> fields that target the outer layers, and to name new fields inner_lx_len.
> 
> Let's discuss the two possibilities.
> 
> 1) outer_lx_len fields are introduced.
> In this case, the stack should have knowledge that it is processing
> tunneled packets to use outer_lx_len rather than lx_len,
> or stack should always use outer_lx_len packet and move those fields to
> lx_len packets if no tunneling occurs...
> I think it will induce extra processing that does not seem to be really
> needed.
> 
> 2) inner_lx_len fields are introduced.
> In this case, the stack first uses lx_len fields. When packet should be
> tunneled, lx_len fields are moved to inner_lx_len fields.
> Then the stack can process the outer layer and still use the lx_len fields.

Not sure, that I understood why 2) is better than 1).
Let say,  you have a 'normal' (non-tunnelling) packet: ether/IP/TCP
In that case you still use mbuf's l2_len/l3_len/l4_len fields and setup ol_flags as usual.
Then later, you decided to 'tunnel' that packet.
So you just fill mbuf's outer_l2_len/outer_l3_len, setup TX_OUTER_* and TX_TUNNEL_* bits in ol_flags and probably update l2_len.
l3_len/l4_len and ol_flags bits set for them remain intact.
That's with 1)

With 2) - you'll have to move l3_len/l4_len to inner_lx_len. 
And I suppose ol_flags values too:
ol_flags &= ~PKT_ IP_CKSUM;
ol_flgas  |=  PKT_INNER_IP_CKSUM
?
And same for L4_CKSUM flags too?

Konstantin

> 
> For  example:
> an eth/IP/TCP forged packet will look like this:
> 
> Ether/IP/UDP/xxx
>    m->flags = IP_CKSUM
>    m->l2_len = sizeof(ether)
>    m->l3_len = sizeof(ip)
>    m->l4_len = sizeof(udp)
>    m->inner_l2_len = 0
>    m->inner_l3_len = 0
> 
> When entering tunnel for example a VXLAN interface, lx_len will be moved
> to inner_lx_len
> 
> Ether/IP/UDP/xxx
>    m->flags = INNER_IP_CKSUM
>    m->l2_len = 0
>    m->l3_len = 0
>    m->l4_len = 0
>    m->inner_l2_len = sizeof(ether)
>    m->inner_l3_len = sizeof(ip)
> 
> 
> once complete encapsulation is processed by the stack, the packet will
> look like
> 
> Ether/IP/UDP/VXLAN/Ether/IP/UDP/xxx
>    m->flags = IP_CKSUM | INNER_IP_CKSUM
>    m->l2_len = sizeof(ether)
>    m->l3_len = sizeof(ip)
>    m->l4_len = sizeof(udp)
>    m->inner_l2_len = sizeof(ether) + sizeof (vxlan)
>    m->inner_l3_len = sizeof(ip)
> 
> 
> didier
>