[dpdk-dev] [PATCH v2] doc: add reserve fields to eventdev public structures

[Kinsella, Ray]

On 04/08/2020 17:20, Stephen Hemminger wrote:
> On Tue, 4 Aug 2020 11:41:53 +0100
> Bruce Richardson <bruce.richardson at intel.com> wrote:
> 
>> On Mon, Aug 03, 2020 at 12:59:03PM +0530, pbhagavatula at marvell.com wrote:
>>> From: Pavan Nikhilesh <pbhagavatula at marvell.com>
>>>
>>> Add 64 byte padding at the end of event device public structure to allow
>>> future extensions.
>>>
>>> Signed-off-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
>>> Acked-by: Jerin Jacob <jerinj at marvell.com>
>>> ---
>>>  v2 Changes:
>>>  - Modify commit title.
>>>  - Add patch reference to doc.
>>>
>>>  doc/guides/rel_notes/deprecation.rst | 11 +++++++++++
>>>  1 file changed, 11 insertions(+)
>>>
>>> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
>>> index ea4cfa7a4..ec5db68e9 100644
>>> --- a/doc/guides/rel_notes/deprecation.rst
>>> +++ b/doc/guides/rel_notes/deprecation.rst
>>> @@ -151,3 +151,14 @@ Deprecation Notices
>>>    Python 2 support will be completely removed in 20.11.
>>>    In 20.08, explicit deprecation warnings will be displayed when running
>>>    scripts with Python 2.
>>> +
>>> +* eventdev: A 64 byte padding is added at the end of the following structures
>>> +  in event device library to support future extensions:
>>> +  ``rte_event_crypto_adapter_conf``, ``rte_event_eth_rx_adapter_conf``,
>>> +  ``rte_event_eth_rx_adapter_queue_conf``, ``rte_event_eth_tx_adapter_conf``,
>>> +  ``rte_event_timer_adapter_conf``, ``rte_event_timer_adapter_info``,
>>> +  ``rte_event_dev_info``, ``rte_event_dev_config``, ``rte_event_queue_conf``,
>>> +  ``rte_event_port_conf``, ``rte_event_timer_adapter``,
>>> +  ``rte_event_timer_adapter_data``.
>>> +  Reference:
>>> +  http://patches.dpdk.org/project/dpdk/list/?series=10728&archive=both&state=*
>>> --  
>>
>> I don't like this idea of adding lots of padding to the ends of these
>> structures. For some structures, such as the public arrays for devices it
>> may be necessary, but for all the conf structures passed as parameters to
>> functions I think we can do better. Since these structures are passed by
>> the user to various functions, function versioning can be used to ensure
>> that the correct function in eventdev is always called. From there to the
>> individual PMDs, we can implement ABI compatibility by either:
>> 1. including the length of the struct as a parameter to the driver. (This is
>>   a bit similar to my proposal for rawdev [1])
>> 2. including the ABI version as a parameter to the driver.
>>
>> Regards
>> /Bruce
>>
>> [1] http://inbox.dpdk.org/dev/?q=enhance+rawdev+APIs
> 
> This is a bad idea.
> 
> Reserved fields won't work because nothing requires that the application
> zero them. You can't start using them later because the application
> may put uninitialized or junk data there.
> 

+1, to Stephens comments.