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

Neil Horman nhorman at tuxdriver.com
Fri Mar 9 01:18:56 CET 2018


On Thu, Mar 08, 2018 at 10:34:14PM +0100, Thomas Monjalon wrote:
> 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.
> 
Thats not entirely true.  It _is_ used to manage ABI changes when backwards
compatibiilty needs to be preserved. It _can_be_ used for experimental abi
management.  That is to say, if you want to modify an existing ABI symbol, you
can do so by writing a new function, and then exporting the new function as the
old symbol with the @EXPERIMENTAL version.  Not saying we have to do that, but
we certainly can, and can eliminate NEXT_ABI in the process.

> I am not saying that I like NEXT_ABI, but it could be useful exceptionnally.
> 
Well, if the consensus is that it should be kept, its no skin off my nose, but
the discussion was around removing NEXT_ABI, and I was copied, so I thought I'd
add my $0.02

Neil

> 
> 


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