Re: [RFC V1 1/1] net: extend VXLAN header to support more extensions

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 2/9/2024 10:12 AM, Thomas Monjalon wrote:
> 09/02/2024 00:54, Ferruh Yigit:
>> On 1/30/2024 11:25 AM, Gavin Li wrote:
>>> Currently, DPDK supports VXLAN and VXLAN-GPE with similar header
>>> structures and we are working on adding support for VXLAN-GBP which is
>>> another extension to VXLAN. More extension of VXLAN may be added in the
>>> future.
>>>
>>> VXLAN and VXLAN-GBP use the same UDP port(4789) while VXLAN-GPE uses a
>>> different one, 4790. The three protocols have the same header length and
>>> overall similar header structure as below.
>>>     0                   1                   2                   3
>>>     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>    |R|R|R|R|I|R|R|R|            Reserved                           |
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>    |                VXLAN Network Identifier (VNI) |   Reserved    |
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>
>>>                            Figure 1: VXLAN Header
>>>
>>>     0                   1                   2                   3
>>>     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>    |R|R|Ver|I|P|B|O|       Reserved                |Next Protocol  |
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>    |                VXLAN Network Identifier (VNI) |   Reserved    |
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>
>>>                          Figure 2: VXLAN-GPE Header
>>>
>>>     0                   1                   2                   3
>>>     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>    |G|R|R|R|I|R|R|R|R|D|R|R|A|R|R|R|        Group Policy ID        |
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>    |          VXLAN Network Identifier (VNI)       |   Reserved    |
>>>    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>
>>>                           Figure 3: VXLAN-GBP Extension
>>>
>>> Both VXLAN-GPE and VXLAN-GBP extended VXLAN by redefining its reserved
>>> bits, which means the packets can be processed with same pattern and most
>>> of the code can be reused. Instead of adding more new items by
>>> copying/pasting code for the VXLAN extensions in the future, it’s better
>>> to use existing VXLAN infrastructure and add support code in it.
>>>
>>
>> Hi Gavin,
>>
>> The motivation is to prevent code duplication, and the code mentioned is
>>  the driver code, right?
> 
> The motivation is mainly to provide a unified and more explicit API.
> 

From user perspective, I think existing approach is more explicit,
because it sets VXLAN or VXLAN_GPE flow types.

I am trying to understand the benefit, how unifying flow type in the API
helps to the user?

>> Overall OK to unify "struct rte_vxlan_hdr" although it makes the struct
>> a little complex, perhaps we can consider extraction some nested structs
>> as named struct, no strong opinion.
>>
>>
>> But not sure about removing the flow item types for VXLAN-GPE, or not
>> adding for VXLAN-GBP.
>>
>> Think about a case user adding a rule, which has a item type as VXLAN
>> and in the protocol header some bits are set, lets say first word, last
>> byte is set, how driver will know if to take it as GPE "next protocol"
>> or "group policy id".
> 
> The driver may decide depending on the UDP port and some distinguishing flags.
> If you want to match on GBP, you should includes the GBP flag in your pattern,
> no need to use a separate item.
> 

Why not be more explicit?
It helps to driver to know more about the pattern to be able to create
proper flow rule, if there is an obvious way for driver to differentiate
these protocol extensions, and flow item type is redundant, I can
understand the proposal, but otherwise I think better to keep flow items
for extensions.

When a rule is set in HW, HW may not care about the protocol, as long as
bits in the rule match with the packet, HW can apply the action.
But for driver to be able to set the rule properly, it needs more
explicit information.


Lets assume driver API get a pattern with 'RTE_FLOW_ITEM_TYPE_VXLAN'
type and "struct rte_flow_item_vxlan", at this point driver doesn't know
if it is VXLAN or any of the extensions.
Should driver go and check GBP flags to deduce if it is GBP flag, and
what if they are all zero, how can driver can tell if this is GBP flag
that is zero or is it VXLAN header and bit is reserved.


Or I will just make up a sample, it may not be accurate but please take
it as a case to prove a point.
Lets assume driver API again get "struct rte_flow_item_vxlan" whose
first word's last bit is set, which union in the struct will driver
check to detect this, GPE one or GBP one?
This can be GPE-"next protocol" or GBP-"Group policy id", if driver
knows this it can set the mask better for the field in the rule.
Driver may try to deduce this extension information from other
information, but why not proper specific flow type for each extension
instead?



>> And if a specific HW detects VXLAN-GPE and VXLAN-GBP protocols as two
>> separate protocols, won't only having capability to describe VXLAN
>> protocol in SW be a limitation.
> 
> I think the driver may know based on the flow rule.
> 
> That's a good question about the item granularity.
> What is the separation between a different protocol and protocol options?
> How flow item should match protocol variations?
> My current thinking is that we should minimize the number of items.
> 
>> If the target is to remove code duplication in the driver, can it be
>> accomplished by extracting code that parse the common fields of these
>> protocols?
> 
> Driver code is not a concern as far as any driver can implement the API.
> 

Got it, I want to clarify this one.
Where the code duplication via copy/paste that commit log mention occurs?

> 
>>> In this patch, all the VXLAN extension header will be merged with VXLAN as
>>> union if the overlapped field has different format among protocols. The
>>> existing VXLAN-GPE will be marked as deprecated and new extensions of
>>> VXLAN should be added to VXLAN instead of a new RTE item.
>>>
>>> Signed-off-by: Gavin Li <gavinl@nvidia.com>
>>> ---
>>>  doc/guides/rel_notes/deprecation.rst |  5 +++
>>>  lib/ethdev/rte_flow.h                | 13 +++++-
>>>  lib/net/rte_vxlan.h                  | 67 ++++++++++++++++++++++++++--
>>>  3 files changed, 80 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
>>> index 81b93515cb..f9cf931b77 100644
>>> --- a/doc/guides/rel_notes/deprecation.rst
>>> +++ b/doc/guides/rel_notes/deprecation.rst
>>> @@ -95,6 +95,11 @@ Deprecation Notices
>>>    - ``rte_flow_item_pppoe``
>>>    - ``rte_flow_item_pppoe_proto_id``
>>>  
>>> +* ethdev: The flow item ``RTE_FLOW_ITEM_TYPE_VXLAN_GPE`` is replaced with ``RTE_FLOW_ITEM_TYPE_VXLAN``.
>>> +  The item ``RTE_FLOW_ITEM_TYPE_VXLAN_GPE``, the struct ``rte_flow_item_vxlan_gpe``, its mask ``rte_flow_item_vxlan_gpe_mask``,
>>> +  and the header struct ``rte_vxlan_gpe_hdr`` with the macro ``RTE_ETHER_VXLAN_GPE_HLEN``
>>> +  will be removed in DPDK 25.11.
>>> +
>>>
>>
>> We have 24.11 in between.
> 
> Isn't it too soon?
> Should we remove at all?
>