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

[Andrew Rybchenko <arybchenko@solarflare.com>]

Hi Olivier,

On 12/27/19 5:50 PM, Olivier Matz wrote:
> 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

Yes, I agree that such behaviour is logical (since PKT_RX_VLAN_STRIPPED is
bound to PKT_RX_VLAN => m->vlan_tci). My understanding was wrong
(see below) since I thought that outer-vlan is saved in vlan_tci in this
case
(since only one is stripped).

> 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.

Yes, I agree.

> 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.

Yes, it would be good, since exactly this cases confuses me.

Many thanks for clarification.

>> 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.