[dpdk-dev] [PATCH v2] doc: plan splitting the ethdev ops struct

[Andrew Rybchenko]

On 2/25/20 7:13 PM, Ferruh Yigit wrote:
> On 2/25/2020 3:51 PM, Andrew Rybchenko wrote:
>> On 2/25/20 3:44 PM, Ferruh Yigit 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>
>>> Acked-by: Jerin Jacob <jerinj at marvell.com>
>>> ---
>>> Cc: David Marchand <david.marchand at redhat.com>
>>> Cc: Thomas Monjalon <thomas at monjalon.net>
>>> Cc: Andrew Rybchenko <arybchenko at solarflare.com>
>>>
>>> v2:
>>> * Add target date for the work
>>> * Give more detail on what will be done
>>> ---
>>>  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 99d81564a..ff612a615 100644
>>> --- a/doc/guides/rel_notes/deprecation.rst
>>> +++ b/doc/guides/rel_notes/deprecation.rst
>>> @@ -86,6 +86,17 @@ 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.
>>> +  Initial split will be done in 20.05 with adding reserved fields for the struct
>>> +  used by inline functions, and by putting new struct reference into public one
>>> +  to not increase the size of ``struct rte_eth_dev``, proper split will be done
>>> +  in 20.11 by moving inline dev_ops function to next to Rx/Tx burst functions and
>>> +  hiding rest.
>>> +
>>>  * 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
>>
>> I'd like to understand why do we need an intermediate solution first.
> 
> We don't need it really, we may prefer to postpone the update to 20.11.
> 
>> Also rereading above few times I've failed to fully understand what
>> will be done and why it does not break API/ABI.
>>
> 
> Agree it wasn't very clear, but I mean something like below, I hope it clarifies:
> 
> Previously:
> 
> struct rte_eth_dev
> 
> +--------+
> |        |    *dev_ops    struct eth_dev_ops
> |        |
> |        +-------------->+--------+
> |        |               |        |
> |        |               |        |
> |        |               |        |
> |        |               |        |
> +--------+               |        |
>                          |        |
>                          |        |
>                          |        |
>                          +--------+
> 
> 
> Proposed:
> 
> struct rte_eth_dev
> 
> +--------+
> |        |                struct eth_dev_ops
> |        |
> |*dev_ops+-------------->+--------+
> |        |               |        |
> |        |               | Reserv |
> |        |               |        |
> |        |               |        |
> +--------+               |        |
>                          +--------+
>                          | inline |
>                          | de^_ops|               struct eth_dev_ops
>                          +--------+
>                          | *priv  +------------->+--------+
>                          +--------+              |        |
>                                                  |        |
>                                                  |        |
>                                                  |        |
>                                                  |        |
>                                                  |        |
>                                                  |        |
>                                                  |        |
>                                                  +--------+
> 
> This is only to keep ABI compatibility [1] while separating the struct.
> 
> [1]
> - The offset of some functions in the dev_ops struct should be same
> - The size of the "struct rte_eth_dev" should be same
> 

OK, got it. Many thanks for explanations.