Re: [dpdk-dev] [PATCH v2 0/7] Removal of PCI bus ABIs

[Thomas Monjalon <thomas@monjalon.net>]

14/10/2021 04:21, Xia, Chenbo:
> From: Thomas Monjalon <thomas@monjalon.net>
> > 13/10/2021 19:56, Walker, Benjamin:
> > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > >
> > > > In order to be perfectly clear, all the changes done around this option
> > > > enable_driver_sdk share the goal of tidying stuff in DPDK so that ABI
> > becomes
> > > > better manageable.
> > > > I think that nobody want to annoy the SPDK project.
> > > > I understand that the changes effectively add troubles, and I am sorry
> > about
> > > > that. If SPDK and other projects can manage with this change, good.
> > > > If there is a real blocker, we should discuss what are the options.
> > > >
> > > > Thanks for your understanding
> > >
> > > I completely understand the desire to make the ABI manageable. If I were in
> > your shoes, I'd be doing the same exact thing. What I don't currently
> > understand is the motivation behind this enable_driver_sdk option. My guess is
> > that it's one of two things.
> > >
> > > \1 ABI manageability: You say that's the purpose above, and that was my
> > initial assumption. But wouldn't that necessarily mean, over time, no longer
> > considering the symbols that were defined by the header files as part of the
> > stable ABI?
> > 
> > Absolutely. The idea is that we don't guarantee ABI for the drivers.
> > 
> > > If you still consider these symbols as part of the ABI in shared library
> > builds, then the enable_driver_sdk option does absolutely nothing to improve
> > the ABI situation, so why bother to have it at all? We can't have packaged
> > SPDK relying on symbols in a packaged DPDK that are not part of the official
> > ABI.
> > 
> > > \2 Not supporting out-of-tree drivers: Another option is that you just don't
> > want people writing out of tree drivers.
> > 
> > We don't want complications due to support of out-of-tree drivers,
> > but we don't want to forbid them.
> > 
> > > You can't just drop it outright because people already do it,
> > > but you'd like to not support it for shared library builds at least.
> > 
> > I didn't think about it in these terms.
> > But saying we don't offer compatibility for shared library drivers
> > is not too far of "no support" indeed.
> > 
> > > So I'd like to really understand which of these two motivated the
> > enable_driver_sdk option . Maybe it's not even one of the two above. If it is
> > #1, then I think maybe we can work with DPDK to define a very small set of
> > out-of-tree driver APIs/ABIs that need to continue to exist in the shared
> > libraries by default. I do think SPDK needs only a very small number. If it's
> > #2, then that's the entire SPDK use case and I'd ask you to reconsider the
> > direction.
> > 
> > Yes I think we need to agree on functions to keep as-is for compatibility.
> > Waiting for your input please.
> 
> So, do you mean currently DPDK doesn't guarantee ABI for drivers

Yes

> but could have driver ABI in the future?

I don't think so, not general compatibility,
but we can think about a way to avoid breaking SPDK specifically,
which has less requirements.