[dpdk-dev] [PATCH v2 0/3] Allow overriding of build-time constants

[Thomas Monjalon]

19/10/2020 12:21, Bruce Richardson:
> On Fri, Oct 16, 2020 at 06:46:12PM +0200, David Marchand wrote:
> > On Fri, Oct 16, 2020 at 5:56 PM Bruce Richardson
> > <bruce.richardson at intel.com> wrote:
> > > > librte_eal.so is indeed built with the 64 value:
> > > > $ pahole -C rte_mem_config build/install/lib64/librte_eal.so |grep memsegs
> > > > die__process_function: tag not supported (INVALID)!
> > > >     struct rte_memseg_list     memsegs[64];          /*   136  8704 */
> > > >
> > > >
> > > > But no trace of the custom value for external applications:
> > > > $ grep -r RTE_MAX_MEMSEG_LISTS build/install
> > > > build/install/include/rte_config.h:#ifndef RTE_MAX_MEMSEG_LISTS
> > > > build/install/include/rte_config.h:#define RTE_MAX_MEMSEG_LISTS 128
> > > > Binary file build/install/lib64/librte_eal.a matches
> > > > Binary file build/install/lib64/librte_eal.so.21.0 matches
> > > >
> > > > I can see the same using the meson option -Dc_args.
> > >
> > > Good point, I had not thought of external apps using these values.
> > >
> > > They are mostly for internal use, so maybe its worthwhile looking to not
> > > have them in a public header file. What do you think? Is it likely that
> > > apps would be using some of these values, or needs to know the specifics?
> > 
> > Some are publicly exposed, like RTE_MEMPOOL_CACHE_MAX_SIZE,
> > RTE_PKTMBUF_HEADROOM, RTE_ETHDEV_RXTX_CALLBACKS,
> > For those, either we propagate the overriden value to the installed
> > rte_config.h or we refuse customisation.
> > 
> I'd suggest the first 2 of those should possibly be global meson options.

How the application is reading the meson options?

> Third should probably not be exposed at all.

I think everything should be exposed.
The application may need to know whether a feature is enabled or not,
and what is a specific tuning value.

I suspect it is the last blocker for meson adoption.
Now that we removed the makefiles, we need to fill this gap urgently.