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

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 17 Feb 2020 15:38:05 +0000
Ferruh Yigit <ferruh.yigit@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@intel.com>
> ---
> Cc: David Marchand <david.marchand@redhat.com>
> Cc: Thomas Monjalon <thomas@monjalon.net>
> Cc: Andrew Rybchenko <arybchenko@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 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.