[dpdk-dev] [PATCH] doc: plan splitting the ethdev ops struct

[Ferruh Yigit]

On 2/25/2020 10:35 AM, Andrew Rybchenko wrote:
> On 2/21/20 1:40 PM, Ferruh Yigit wrote:
>> On 2/18/2020 6:01 AM, Stephen Hemminger wrote:
>>> On Mon, 17 Feb 2020 15:38:05 +0000
>>> Ferruh Yigit <ferruh.yigit at intel.com> wrote:
>>>
>>>> For the ABI compatibility it is better to hide internal data structures
>>>> from the application as much as possible. But because of some inline
>>>> functions 'struct eth_dev_ops' can't be hidden completely.
>>>>
>>>> Plan is to split the 'struct eth_dev_ops' into two as ones used by
>>>> inline functions and ones not used, and hide the second part that not
>>>> used by inline functions completely to the application.
>>>>
>>>> Signed-off-by: Ferruh Yigit <ferruh.yigit at intel.com>
>>>> ---
>>>> Cc: David Marchand <david.marchand at redhat.com>
>>>> Cc: Thomas Monjalon <thomas at monjalon.net>
>>>> Cc: Andrew Rybchenko <arybchenko at solarflare.com>
>>>> ---
>>>>  doc/guides/rel_notes/deprecation.rst | 6 ++++++
>>>>  1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
>>>> index dfcca87ab..2aa431028 100644
>>>> --- a/doc/guides/rel_notes/deprecation.rst
>>>> +++ b/doc/guides/rel_notes/deprecation.rst
>>>> @@ -72,6 +72,12 @@ Deprecation Notices
>>>>    In 19.11 PMDs will still update the field even when the offload is not
>>>>    enabled.
>>>>  
>>>> +* ethdev: Split the ``struct eth_dev_ops`` struct to hide it as much as possible.
>>>> +  Currently the ``struct eth_dev_ops`` struct is accessible by the application
>>>> +  because some inline functions, like ``rte_eth_tx_descriptor_status()``,
>>>> +  access the struct directly. The struct will be separate in two, the ops used
>>>> +  by inline functions still will be accessible to user but rest will be hidden.
>>>> +
>>>>  * cryptodev: support for using IV with all sizes is added, J0 still can
>>>>    be used but only when IV length in following structs ``rte_crypto_auth_xform``,
>>>>    ``rte_crypto_aead_xform`` is set to zero. When IV length is greater or equal
>>>
>>> Good luck, truely hiding internals is hard. The mbuf structure is already split but not really
>>> hidden at all (just look at dwarf output). It doesn't make sense to do it unless
>>> you can really hide it.
>>
>> I believe this can be done, only following [1] dev_ops are used by inline
>> functions, rest can be moved into separate struct and moved into ethdev driver
>> looking header.
>>
>> [1]
>> rx_queue_count
>> rx_descriptor_done
>> rx_descriptor_status
>> tx_descriptor_status
> 
> I think having 3 places (if I understand the intention
> correctly) with ethdev callbacks is too much. 

Yes, this is the intention.

> So, I think
> that these ops should be simply moved to nearby Tx/Rx
> burst and Tx prepare callbacks (e.g. move into inline_ops
> structure which is located at the beginning of rte_eth_dev
> in order to preserve 3 existing callback location).

I think this is reasonable, but this can be done only in 20.11 with ABI break.

What do you think doing the initial hide in 20.05 with three places and do
proper splitting in 20.11 as suggested above.

Or it is possible to drop the interim work and do the all changes in 20.11, not
sure.


> 
> Also I'd consider to deprecate and remove rx_queue_count
> and rx_descriptor_done.

+1 to deprecate the 'rx_descriptor_done', we have already 'rx_descriptor_status'
& 'tx_descriptor_status' to replace the functionality.

@Thomas, @Ray, can you please remind how deprecation was done, is it marking
API, 'rte_eth_rx_descriptor_done', as deprecated in 20.11 and removing it in
21.11? If so I guess deprecation notice should be send before 20.11? (And make
sure all PMDs did the switch before 20.11)


Not sure about 'rx_queue_count', if any application may need it or not.

> 
>>>
>>> I would attack the rte_device stuff first. Make rte_device opaque to the application
>>> that would help for future versions. Then work backwards to rte_tehtdev.
>>>
>