Re: [PATCHv4 3/5] Makefiles: Add experimental tag check and warnings to trigger on use

[Thomas Monjalon <thomas@monjalon.net>]

22/01/2018 02:34, Neil Horman:
> On Sun, Jan 21, 2018 at 07:54:44PM +0100, Thomas Monjalon wrote:
> > 12/01/2018 13:44, Neil Horman:
> > > On Fri, Jan 12, 2018 at 11:49:57AM +0000, Ferruh Yigit wrote:
> > > > On 1/11/2018 8:50 PM, Neil Horman wrote:
> > > > > On Thu, Jan 11, 2018 at 08:06:43PM +0000, Ferruh Yigit wrote:
> > > > >> On 12/13/2017 3:17 PM, Neil Horman wrote:
> > > > >>> --- a/app/test-eventdev/Makefile
> > > > >>> +++ b/app/test-eventdev/Makefile
> > > > >>> @@ -32,6 +32,7 @@ include $(RTE_SDK)/mk/rte.vars.mk
> > > > >>>  
> > > > >>>  APP = dpdk-test-eventdev
> > > > >>>  
> > > > >>> +CFLAGS += -DALLOW_EXPERIMENTAL_APIS
> > > > >>
> > > > >> Do we need this internally in DPDK? For application developers this is great,
> > > > >> they will get warning unless explicitly stated that they are OK with it.
> > > > >>
> > > > > I'm not sure what you're asking here.  As I mentioned in the initial post, I
> > > > > think we should give blanket permission to any in-tree dpdk library to allow the
> > > > > use of experimental API's, but that doesn't really imply that all developers
> > > > > would wan't it disabled all the time.  That is to say, I could envision a
> > > > > library author who, early in development would want to get a warning issued if
> > > > > they used an unstable API, and, only once they were happy with their design and
> > > > > choice of API usage, turn the warning off.
> > > > 
> > > > I got your point, but I think whoever using an experimental API in another
> > > > component in DPDK is almost always the author of the that experimental API, so
> > > > not sure this check is ever really needed within dpdk.
> > > > 
> > > I would have thought so too, but it doesn't really bear up.  The example I used
> > > to convince myself of a more granular approach was commit
> > > 9c38b704d280ac128003238d7d80bf07fa556a7d where the rte_service API was
> > > introduced as experimental by Nikhil Rao, and then later used in the eal library
> > > as part of commit a894d4815f79b0d76527d9c42b23327de1501711 by Harry van Haaren.
> > > Its no big deal because, as we agree, internal usage should be considered safe,
> > > but it seemed clear that differing authors were using each others code
> > > (potentially oblivious to the experimental nature of those APIs)
> > > 
> > > > But OK, I guess it won't hurt to have more granular approach.
> > > > 
> > > > > 
> > > > >> Do we have any option than allowing them in DPDK library? And when experimental
> > > > >> API modified the users in the DPDK library internally guaranteed to be updated.
> > > > >> Why not globally allow this for all DPDK internally?
> > > > >>
> > > > > For the reason I gave above.  We certainly could enable this in a more top-level
> > > > > makefile so that for in-library systems it was opt-in rather than opt-out, but I
> > > > > chose a more granular approach because I could envision newer libraries wanting
> > > > > it on.  I also felt, generally speaking, that where warning flags were
> > > > > concerned, it generally desireous to have them on by default, and make people
> > > > > explicitly choose to turn them off.
> > 
> > I think DPDK developpers look at the EXPERIMENTAL warning in the doxygen
> > above the prototype.
> I'm not sure I agree with that, but regardless, my initial reasoning for writing
> this tag was to call attention to experimental API's during review, rather than
> their use during development, so I didn't gripe about ABI changes on expemted
> code.   Additionally, weather they look at the docs or not, they can
> pre-emptively turn off the warning if they choose.
> 
> > And when API will be switched to stable, we probably won't remove the flag
> > in the makefile to disable allowing experimental.
> Well, that remains to be seen I suppose.
> 
> > So at the end, we could just allow experimental API for all internal libs.
> Thats a rather bootstrapping argument.  You are effecitvely saying that no one
> developing will ever want to be warned of using experimental APIs in DPDK, so
> lets just turn it off everyone.  I would really rather let individual developers
> make that call at the time they author something new.

I don't see the benefit,
but I am OK to keep it like this.