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

[Andrew Rybchenko]

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. 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).

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

>>
>> 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.
>>