[dpdk-dev] [RFC] mbuf: support dynamic fields and flags

[Thomas Monjalon]

10/07/2019 11:29, Olivier Matz:
> Many features require to store data inside the mbuf. As the room in mbuf
> structure is limited, it is not possible to have a field for each
> feature. Also, changing fields in the mbuf structure can break the API
> or ABI.
> 
> This commit addresses these issues, by enabling the dynamic registration
> of fields or flags:
> 
> - a dynamic field is a named area in the rte_mbuf structure, with a
>   given size (>= 1 byte) and alignment constraint.
> - a dynamic flag is a named bit in the rte_mbuf structure.
> 
> The typical use case is a PMD that registers space for an offload
> feature, when the application requests to enable this feature.  As
> the space in mbuf is limited, the space should only be reserved if it
> is going to be used (i.e when the application explicitly asks for it).
> 
> The registration can be done at any moment, but it is not possible
> to unregister fields or flags for now.
> 
> Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>

I fully support this solution.
It will give a lot of space for new features and will solve
the ABI stability problem.

Next step, I would like to move some existing mbuf fields to this
dynamic model. It will increase the free space in mbuf to be used
by dynamic fields. By converting some fields which are currently
union'ed, we can also fix the issue of these features being exclusive.

Acked-by: Thomas Monjalon <thomas at monjalon.net>