Re: [dpdk-dev] [PATCH] doc: announce flow API matching pattern struct changes

[Ori Kam <orika@nvidia.com>]

Hi

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@intel.com>
> Sent: Monday, November 23, 2020 5:51 PM
> Subject: Re: [PATCH] doc: announce flow API matching pattern struct changes
> 
> On 11/23/2020 2:25 PM, Andrew Rybchenko wrote:
> > On 11/23/20 5:17 PM, Ferruh Yigit wrote:
> >> On 11/23/2020 1:50 PM, Andrew Rybchenko wrote:
> >>> On 11/23/20 4:40 PM, Ferruh Yigit wrote:
> >>>> Proposing to replace protocol header fields in the ``rte_flow_item_*``
> >>>> structures with the protocol structs, like:
> >>>>
> >>>> Current ``struct rte_flow_item_eth``,
> >>>>
> >>>> struct rte_flow_item_eth {
> >>>>      struct rte_ether_addr dst;
> >>>>      struct rte_ether_addr src;
> >>>>      rte_be16_t type;
> >>>>      uint32_t has_vlan:1;
> >>>>      uint32_t reserved:31;
> >>>> }
> >>>>
> >>>> will become
> >>>>
> >>>> struct rte_flow_item_eth {
> >>>>      struct rte_ether_hdr hdr;
> >>>>      uint32_t has_vlan:1;
> >>>>      uint32_t reserved:31;
> >>>> }
> >>>>
> >>>> This is both for documenting the intention and to be sure
> >>>> ``rte_flow_item_*`` always starts with complete protocol header.
> >>>>
> >>>> Already many ``rte_flow_item_*`` structs implemented to have protocol
> >>>> struct, target is convert all to this usage.
> >>>>
> >>>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
> >>>
> >>> Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> >>>
> >>> a minor note below
> >>>
> >>>> ---
> >>>> Cc: Thomas Monjalon <thomas@monjalon.net>
> >>>> Cc: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> >>>> Cc: Ori Kam <orika@nvidia.com>
> >>>> ---
> >>>>    doc/guides/rel_notes/deprecation.rst | 7 +++++++
> >>>>    1 file changed, 7 insertions(+)
> >>>>
> >>>> diff --git a/doc/guides/rel_notes/deprecation.rst
> >>>> b/doc/guides/rel_notes/deprecation.rst
> >>>> index 96986fabd598..a2fa0c196472 100644
> >>>> --- a/doc/guides/rel_notes/deprecation.rst
> >>>> +++ b/doc/guides/rel_notes/deprecation.rst
> >>>> @@ -88,6 +88,13 @@ Deprecation Notices
> >>>>      will be limited to maximum 256 queues.
> >>>>      Also compile time flag ``RTE_ETHDEV_QUEUE_STAT_CNTRS`` will be
> >>>> removed.
> >>>>    +* ethdev: The flow API matching pattern structures, ``struct
> >>>> rte_flow_item_*``,
> >>>> +  should start with relevant protocol header.
> >>>> +  Some matching pattern structures implements this by duplicating
> >>>> protocol header
> >>>> +  fields in the struct. To clarify the intention and to be sure
> >>>> protocol header
> >>>> +  is intact, will replace those fields with relevant protocol
> >>>> header struct.
> >>>> +  Target is v21.02 release and this should not change the ABI.
> >>>> +
> >>>>    * sched: To allow more traffic classes, flexible mapping of pipe
> >>>> queues to
> >>>>      traffic classes, and subport level configuration of pipes and
> >>>> queues
> >>>>      changes will be made to macros, data structures and API
> >>>> functions defined
> >>>>
> >>>
> >>> Just want to highlight that even API could be kept using
> >>> unnamed union for hdr and unnamed structure for existing
> >>> protocol header fields.
> >>>
> >>
> >> Then we may never clean the protocol header fields out of it,
> >> yes this will impact the user but I believe the impact is small and
> >> trivial,
> >> I prefer replacing fields with protocol struct.
> >
> > The problem that API breakages are bad and, for example, OvS uses these
> > fields.
> >
> > May be API breakage should be postponed to 21.11?
> >
> 
> Agree but it is not as bad as ABI break, if user is already compiling their
> code, it is not too bad to adjust the struct for changes, and the changes are
> straightforward.
> 
I'm not sure which is worse ABI or API, API is more straight forward but all apps must be modified,
while ABI is hidden and happens only in rare cases.
In a addition it may result in large number of changes (simple but large number)

> But if, somehow, application needs to support multiple version of the DPDK it
> can be headache.
> 

Agree, 

> We may go with your suggestion until 21.11, and do the cleanup on 21.11, will
> it
> work?
+1 also when considering my next line,

One more point to consider what happens to struct that are not according to spec,
for example mpls, geneve where the struct is different than the item.