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

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, May 22, 2019 at 04:22:53PM +0000, Jerin Jacob Kollanukkaran wrote:
> > -----Original Message-----
> > From: Neil Horman <nhorman@tuxdriver.com>
> > Sent: Wednesday, May 22, 2019 9:09 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: Re: [EXT] Re: [dpdk-dev] Re: [PATCH] devtools: skip the symbol
> > check when map file under drivers
> > 
> > On Wed, May 22, 2019 at 02:25:14PM +0000, Jerin Jacob Kollanukkaran wrote:
> > > > -----Original Message-----
> > > > From: Neil Horman <nhorman@tuxdriver.com>
> > > > Sent: Wednesday, May 22, 2019 7:41 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 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
> > >
> > > 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


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
> > >
> > >
>