Re: [dpdk-dev] [RFC] config: remove RTE_NEXT_ABI

[Thomas Monjalon <thomas@monjalon.net>]

08/03/2018 20:40, Neil Horman:
> On Thu, Mar 08, 2018 at 05:04:01PM +0100, Thomas Monjalon wrote:
> > 08/03/2018 16:35, Neil Horman:
> > > On Thu, Mar 08, 2018 at 04:17:00PM +0100, Thomas Monjalon wrote:
> > > > 08/03/2018 12:43, Ferruh Yigit:
> > > > > On 3/8/2018 8:05 AM, Thomas Monjalon wrote:
> > > > > > 07/03/2018 18:44, Ferruh Yigit:
> > > > > >> After experimental API process defined do we still need RTE_NEXT_ABI
> > > > > >> config and process which has similar targets?
> > > > > > 
> > > > > > They are different targets.
> > > > > > Experimental API is always enabled but may be avoided by applications.
> > > > > > Next ABI can be used to break ABI without notice and disabled to keep
> > > > > > old ABI compatibility. It is almost never used because it is preferred
> > > > > > to keep ABI compatibility with rte_compat macros, or wait a deprecation
> > > > > > period after notice.
> > > > > 
> > > > > OK, I see.
> > > > > 
> > > > > Shouldn't we disable it by default at least? Otherwise who is not paying
> > > > > attention to this config option will get and ABI/API break.
> > > > 
> > > > Yes I think you are right, it can be disabled by default.
> > > > 
> > > I would agree, there seems to be overlap here, and the experimental tagging can
> > > cover what the NEXT_API flag is meant to do.  It can be removed I think.
> > 
> > It is not NEXT_API but NEXT_ABI.
> Sorry, typo, though I'm sure you got that, since the former doesn't exist,
> right?
> > Why do you think it overlaps experimental API tagging?
> 
> I assert that because the compat lib has macros to map common symbols to version
> specific ones.  That is to say, if you change a data structure, you can setup
> the API calls that use said structure such that version 1 or the symbol maps to
> an internal function that uses the old structure, while version 2 maps to an
> internal function that uses the new symbol
> 
> That is to say, if you're planning on introducing ABI changes, the experimental
> API tagging can be used to implement what the NEXT_ABI macro does.

It is a different usage.
Experimental API tagging is for new functions.
rte_compat is used to avoid breaking the ABI when changing old code.
NEXT_ABI has been used in the past to disable an ABI breakage, which was
not possible to mitigate with rte_compat because impacting too many functions.

I am not saying that I like NEXT_ABI, but it could be useful exceptionnally.