[dpdk-dev] [PATCH] devtools: skip the symbol check when map file under drivers

[Jerin Jacob Kollanukkaran]

> -----Original Message-----
> From: Neil Horman <nhorman at tuxdriver.com>
> Sent: Thursday, May 23, 2019 12:29 AM
> To: Jerin Jacob Kollanukkaran <jerinj at marvell.com>
> Cc: Bruce Richardson <bruce.richardson at intel.com>; dev at dpdk.org;
> thomas at monjalon.net; stable at dpdk.org
> Subject: Re: [EXT] Re: [dpdk-dev] Re: [PATCH] devtools: skip the symbol
> check when map file under drivers
> > > > > > IMO, The name prefix matters. The rte_* should denote it a
> > > > > > DPDK API and application suppose to use it.
> > > > > >
> > > > > It doesn't, its just a convention.  We have no documentation
> > > > > that indicates what the meaning of an rte_* prefix is
> > > > > specficially, above and beyond the fact thats how we name
> > > > > functions in the DPDK.  If you want to submit a patch to
> > > > > formalize the meaning of function prefixes, you're welcome too
> > > > > (though I won't support it, perhaps others will).  But even if
> > > > > you do, it doesn't address the underlying problem, which is that
> applications still have access to those symbols.
> > > > > Maintaining an ABI by assertion of prefix is really a lousy way
> > > > > to communicate what functions should be accessed by an
> > > > > application and which shouldn't.  If a function is exported, and
> > > > > included in the header file, people will try to use
> > > >
> > > > The current scheme in the driver/common is that, the header files
> > > > are NOT made It as public ie not installed make install.
> > > > The consumer driver includes that using relative path wrt DPDK
> > > > source
> > > directory.
> > > >
> > > Well, thats a step in the right direction.  I'd still like to see
> > > some enforcement to prevent the inadvertent use of those APIs though
> >
> > Yes header file  is  not exported. Not sure how a client can use those.
> > Other than doing some hacking.
> >
> Yes, self prototyping the exported functions would be a way around that.
> > >
> > > > Anyway I will add experimental section to make tool happy.
> > > >
> > > That really not the right solution.  Marking them as experimental is
> > > just papering over the problem, and suggests to users that they will
> > > one day be stable.
> >
> > That what my original concern.
> >
> > > What you want is to explicitly mark those symbols as internal only,
> > > so that any inadvertent use gets flagged.
> >
> > What is your final thought? I can assume the following for my patch
> > generation
> >
> > # No need to mark as experimental
> > # Add @internal to denote it is a internal function like followed some places
> in EAL.
> >
> These are both correct, yes.
> 
> In addition, I would like to see some mechanism that explicitly marks the
> function as exported only for the purposes of internal use.  I understand that
> yours is a case in which this is not expressly needed because you don't
> prototype those functions, but what I'd like to see is a macro in rte_compat.h
> somewhere like this:
> 
> #define INTERNAL_USE_ONLY do {static_assert(0, "Function is only available
> for internal DPDK usage");} while(0)
> 
> so that, in your exported header file (of which I'm sure you have one, even if
> it doesn't contain your private functions, you can do something like this:
> 
> #ifdef BUILDING_RTE_SDK
> void somefunc(int val);
> #else
> #define somefunc(x) INTERNAL_USE_ONLY
> #endif

I think, We have two cases
1) Internal functions are NOT available via  DPDK SDK exported header files
2) Internal functions are available via DPDK SDK exported header files

I think, you are trying to address case 2( as case 1 is not applicable in this context due lack of header file)
For case 2, IMO, the above scheme will not be enough as 
The consumer entity can simply add the exact C flags to skip that check in this case, -DBUILDING_RTE_SDK.
IMO, it would be correct remove private functions from public header files. No strong options on this.
 
> 
> This combination allows for 'internal' functions to be used (defining internal
> to mean access to functions only when building the DPDK SDK), while
> expressly breaking the build of any application which attempts to use these
> functions when not building the SDK (i.e. when building an application that
> expects to link to the DPDK after its built).  Again, I uderstand that in your
> case, it may be sufficient to just not prototype the functions you don't want
> used, but I think in the general case its important to have some mechanism
> to expressly prevent their usage outside the SDK
> 
> Best
> Neil
> 
> > >
> > > Neil
> > > >
> > > >
> >