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

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, May 22, 2019 at 01:41:03PM +0000, Jerin Jacob Kollanukkaran wrote:
> > -----Original Message-----
> > From: Neil Horman <nhorman@tuxdriver.com>
> > Sent: Wednesday, May 22, 2019 6:43 PM
> > To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
> > Cc: Bruce Richardson <bruce.richardson@intel.com>; dev@dpdk.org;
> > thomas@monjalon.net; stable@dpdk.org
> > Subject: [EXT] Re: [dpdk-dev] Re: [PATCH] devtools: skip the symbol check
> > when map file under drivers
> > 
> > External Email
> > 
> > ----------------------------------------------------------------------
> > On Wed, May 22, 2019 at 11:54:13AM +0000, Jerin Jacob Kollanukkaran
> > wrote:
> > > > -----Original Message-----
> > > > From: Bruce Richardson <bruce.richardson@intel.com>
> > > > Sent: Wednesday, May 22, 2019 4:21 PM
> > > > To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
> > > > Cc: Neil Horman <nhorman@tuxdriver.com>; dev@dpdk.org;
> > > > thomas@monjalon.net; stable@dpdk.org
> > > > Subject: Re: [dpdk-dev] [EXT] Re: [PATCH] devtools: skip the symbol
> > > > check when map file under drivers
> > > >
> > > > > > Sorry, but I'm not ok with this, because many of our DPDK PMDs
> > > > > > have functions that get exported which are meant to be called by
> > > > > > applications directly.  The
> > > > >
> > > > > OK. Just to update my knowledge, Should those API needs to go
> > > > > through ABI/API depreciation process?
> > > > >
> > > > > Actually, I am concerned about the APIs, which is called between
> > > > > drviers not the application. For example,
> > > > > drivers/common/dpaax/rte_common_dpaax_version.map
> > > > >
> > > > > it is not interface to application rather it is for intra driver case.
> > > > > I think, I can change my logic to Skip the symbols which NOT
> > > > > starting with
> > > > rte_.
> > > > > Agree?
> > > > >
> > > > > Context:
> > > > > I am adding a new driver/common/octeontx2 directory and it has
> > > > > some API which Needs to shared between drivers not to the
> > > > > application. For me, it does not make sense to go through any ABI
> > process in such case.
> > > > >
> > > > >
> > > > Maybe not, but other drivers will have APIs designed for apps to
> > > > call directly - some NIC drivers have them, and I suspect that
> > > > rawdev drivers will need them a lot. Therefore, it's best to have
> > > > the drivers directory scanned by our tooling.
> > >
> > > Agreed. But all of those API  which called directly called from
> > > application is starts with rte_ symbol. How about skipping the symbols
> > > which is NOT start with rte_*
> > > example:
> > > drivers/common/octeontx/rte_common_octeontx_version.map
> > > drivers/common/dpaax/rte_common_dpaax_version.map
> > >
> > 
> > No, that won't work.  If you export a function, it doesn't matter if its named
> > rte_* or not.  Its accessible from any library/application that cares to call it,
> 
> 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
them.  You need an enforcement mechanism to call attention to the fact that they
are unusable in normal operation

> I don't think, giving experimental status to intra driver API helps anyone, neither driver nor
> application.
> 
Nor do I, I was just using it as an example of how you might create an
enforcement mechanism.  I think a better solution is bifurcating your headers
to a public and private version, in which the former defines apis you wish to be
generally inaccessable to a static_assert that causes a build time error for
uses that are not 'DPDK internal'

> If you think strongly that experimental needs to be added for intra driver APIs then I can add that.
>  
No, I don't, I was just using that as an example of what you might do.  I think
the header solution is far more appropriate for this case.

Neil