Re: [PATCH v2 01/10] ethdev: introduce flow pre-configuration hints

[Thomas Monjalon <thomas@monjalon.net>]

24/01/2022 15:36, Jerin Jacob:
> On Tue, Jan 18, 2022 at 9:01 PM Alexander Kozyrev <akozyrev@nvidia.com> wrote:
> > +struct rte_flow_port_attr {
> > +       /**
> > +        * Version of the struct layout, should be 0.
> > +        */
> > +       uint32_t version;
> 
> Why version number? Across DPDK, we are using dynamic function
> versioning, I think, that would be sufficient for ABI versioning

Function versioning is not ideal when the structure is accessed
in many places like many drivers and library functions.

The idea of this version field (which can be a bitfield)
is to update it when some new features are added,
so the users of the struct can check if a feature is there
before trying to use it.
It means a bit more code in the functions, but avoid duplicating functions
as in function versioning.

Another approach was suggested by Bruce, and applied to dmadev.
It is assuming we only add new fields at the end (no removal),
and focus on the size of the struct.
By passing sizeof as an extra parameter, the function knows
which fields are OK to use.
Example: http://code.dpdk.org/dpdk/v21.11/source/lib/dmadev/rte_dmadev.c#L476