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

[Andrew Rybchenko <arybchenko@solarflare.com>]

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.