Re: [dpdk-dev] [RFC PATCH] mbuf: fix to update documentation of PKT_RX_QINQ_STRIPPED

[Olivier Matz <olivier.matz@6wind.com>]

Hi,

On Tue, Dec 24, 2019 at 12:53:21PM +0300, Andrew Rybchenko wrote:
> On 12/24/19 6:16 AM, Somnath Kotur wrote:
> > Given that we haven't heard any objection from anyone in a while on
> > this ...can we get this in please?
> 
> I'm sorry, but have you seen below?
> It means that PKT_RX_QINQ_STRIPPED, PKT_RX_QINQ, PKT_RX_VLAN
> and PKT_RX_VLAN_STRIPPED must be clarified.
> 
> It sounds like change of semantics in order to resolve the
> problem, but anyway it is still a small change of semantics.

Let's take this packet:
packet = ether | outer-vlan | inner-vlan | ...

The possible mbufs received from a PMD, depending on configuration, are:

1/ no flag (no offload)

2/ PKT_RX_VLAN
   packet data is unmodified
   m->vlan_tci=outer-vlan

3/ PKT_RX_VLAN | PKT_RX_VLAN_STRIPPED
   outer-vlan is removed from packet data
   m->vlan_tci=outer-vlan

4/ PKT_RX_VLAN | PKT_RX_QINQ
   packet data is unmodified
   m->vlan_tci_outer=outer-vlan
   m->vlan_tci=inner-vlan

5/ PKT_RX_VLAN | PKT_RX_VLAN_STRIPPED | PKT_RX_QINQ

   from PKT_RX_VLAN_STRIPPED:
     A vlan has been stripped by the hardware and its tci is saved in
     mbuf->vlan_tci.
   from PKT_RX_QINQ:
     The RX packet is a double VLAN, and the outer tci has been
     saved in in mbuf->vlan_tci_outer.

   To me, it means:

   inner-vlan is removed from packet data
   m->vlan_tci_outer=outer-vlan
   m->vlan_tci=inner-vlan

6/ PKT_RX_VLAN | PKT_RX_VLAN_STRIPPED | PKT_RX_QINQ | PKT_RX_QINQ_STRIPPED
   both outer-vlan and inner-vlan removed from packet data
   m->vlan_tci_outer=outer-vlan
   m->vlan_tci=inner-vlan

Other flag combinations are not supported.
The proposed patch documents that this new flag combination is now allowed:

7/ PKT_RX_VLAN | PKT_RX_QINQ | PKT_RX_QINQ_STRIPPED
   outer-vlan is removed from packet data
   m->vlan_tci_outer=outer-vlan
   m->vlan_tci=inner-vlan

Except if I missed something, I don't see any semantic change in
the previously supported cases.

I think we should by the way clarify what happens in 5/, probably by
saying somewhere that as soon as PKT_RX_QINQ is set, PKT_RX_VLAN*
refer to inner vlan.


> BTW, it is better to make summary human readable and avoid
> PKT_RX_QINQ_STRIPPED (I guess check-git-log.sh yells on it).
> 
> Also RFC patch cannot be applied, non-RFC version is required.
> 
> CC main tree maintainers.
> 
> > Thanks
> > 
> > On Mon, Dec 16, 2019 at 2:43 PM Andrew Rybchenko
> > <arybchenko@solarflare.com> wrote:
> >>
> >> On 12/16/19 11:47 AM, Somnath Kotur wrote:
> >>> On Mon, Dec 16, 2019 at 12:01 PM Andrew Rybchenko
> >>> <arybchenko@solarflare.com> wrote:
> >>>>
> >>>> On 12/16/19 6:16 AM, Somnath Kotur wrote:
> >>>>> Certain hardware may be able to strip and/or save only the outermost
> >>>>> VLAN instead of both the VLANs in the mbuf in a QinQ scenario.
> >>>>> To handle such cases, we could re-interpret setting of just PKT_RX_QINQ_STRIPPED
> >>>>> to indicate that only the outermost VLAN has been stripped by the hardware and
> >>>>> saved in mbuf->vlan_tci_outer.
> >>>>> Only When both PKT_RX_QINQ_STRIPPED and PKT_RX_VLAN_STRIPPED are set, the 2 vlans
> >>>>> have been stripped by the hardware and their tci are saved in mbuf->vlan_tci (inner)
> >>>>> and mbuf->vlan_tci_outer (outer).
> >>>>>
> >>>>> Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
> >>>>> Signed-off-by: JP Lee <jongpil.lee@broadcom.com>
> >>>>> ---
> >>>>>  lib/librte_mbuf/rte_mbuf_core.h | 15 +++++++++++----
> >>>>>  1 file changed, 11 insertions(+), 4 deletions(-)
> >>>>>
> >>>>> diff --git a/lib/librte_mbuf/rte_mbuf_core.h b/lib/librte_mbuf/rte_mbuf_core.h
> >>>>> index 9a8557d..db1070b 100644
> >>>>> --- a/lib/librte_mbuf/rte_mbuf_core.h
> >>>>> +++ b/lib/librte_mbuf/rte_mbuf_core.h
> >>>>> @@ -124,12 +124,19 @@
> >>>>>  #define PKT_RX_FDIR_FLX      (1ULL << 14)
> >>>>>
> >>>>>  /**
> >>>>> - * The 2 vlans have been stripped by the hardware and their tci are
> >>>>> - * saved in mbuf->vlan_tci (inner) and mbuf->vlan_tci_outer (outer).
> >>>>> + * The outer vlan has been stripped by the hardware and their tci are
> >>>>> + * saved in mbuf->vlan_tci_outer (outer).
> >>>>>   * This can only happen if vlan stripping is enabled in the RX
> >>>>>   * configuration of the PMD.
> >>>>> - * When PKT_RX_QINQ_STRIPPED is set, the flags (PKT_RX_VLAN |
> >>>>> - * PKT_RX_VLAN_STRIPPED | PKT_RX_QINQ) must also be set.
> >>>>> + * When PKT_RX_QINQ_STRIPPED is set, the flags (PKT_RX_VLAN |  PKT_RX_QINQ)
> >>>>> + * must also be set.
> >>>>> + * When both PKT_RX_QINQ_STRIPPED and PKT_RX_VLAN_STRIPPED are set, the 2 vlans
> >>>>> + * have been stripped by the hardware and their tci are saved in
> >>>>> + * mbuf->vlan_tci (inner) and mbuf->vlan_tci_outer (outer).
> >>>>> + * This can only happen if vlan stripping is enabled in the RX configuration
> >>>>> + * of the PMD.
> >>>>> + * When PKT_RX_QINQ_STRIPPED and PKT_RX_VLAN_STRIPPED are set,
> >>>>> + * (PKT_RX_VLAN | PKT_RX_QINQ) must also be set.
> >>>>>   */
> >>>>>  #define PKT_RX_QINQ_STRIPPED (1ULL << 15)
> >>>>>
> >>>>
> >>>> I always thought that PKT_RX_VLAN_STRIPPED means *one* VLAN
> >>>> stripped regardless if it is outer (if the packet is double
> >>>> tagged) or inner (if only one VLAN tag was present).
> >>>>
> >>>> That's why PKT_RX_QINQ_STRIPPED description says that *two*
> >>>> VLANs have been stripped.
> >>>>
> >>>> What is the problem with such approach?
> >>> The problem is that RX_VLAN_STRIPPED implies that the stripped VLAN
> >>> (outer or inner) is saved in mbuf->vlan_tci, correct?
> >>
> >> Yes.
> >>
> >>> There is no way to convey that it is in QinQ mode and yet only outer
> >>> VLAN has been stripped and saved in mbuf->vlan_tci_outer ?
> >>
> >> Ah, it looks like I understand now that the problem is in
> >> PKT_RX_QINQ description which claims that TCI is saved in
> >> mbuf->vlan_tci_outer and PKT_RX_QINQ_STRIPPED means that
> >> both VLAN tags are stripped regardless (PKT_RX_VLAN_STRIPPED).
> >> Moreover PKT_RX_QINQ_STRIPPED requires PKT_RX_VLAN_STRIPPED.
> >>
> >> It means that PKT_RX_QINQ_STRIPPED, PKT_RX_QINQ, PKT_RX_VLAN
> >> and PKT_RX_VLAN_STRIPPED must be clarified.
> >>
> >> I'm not sure, but it looks like it could affect net/dpaa2,
> >> so I'm including driver maintainers in CC.
>