Re: [dpdk-stable] [dpdk-dev] [PATCH v5 04/17] build: define _GNU_SOURCE globally

[Thomas Monjalon <thomas@monjalon.net>]

26/02/2021 11:04, Thomas Monjalon:
> 26/02/2021 10:46, Bruce Richardson:
> > On Fri, Feb 26, 2021 at 10:40:32AM +0100, Thomas Monjalon wrote:
> > > 26/02/2021 10:08, Bruce Richardson:
> > > > On Thu, Feb 25, 2021 at 07:22:37PM +0100, Thomas Monjalon wrote:
> > > > > There was an intent to define _GNU_SOURCE globally,
> > > > > but it was not set in pkg-config for external applications.
> > > > > 
> > > > Is this something that we really want to do, to force all external apps to
> > > > use _GNU_SOURCE when compiling? Do some of our header files rely on
> > > > definitions only available with _GNU_SOURCE? If so, we should probably look
> > > > to remove that dependency rather than mandating the define.
> > > 
> > > From patch 5:
> > > In musl libc, cpu_set_t is defined only if _GNU_SOURCE is defined.
> > > 
> > > If we avoid mandating _GNU_SOURCE,
> > > we must #ifdef functions relying on rte_cpuset_t in the headers:
> > > 	- rte_lcore_cpuset
> > > 	- rte_thread_set_affinity
> > > 	- rte_thread_get_affinity
> > > 	- rte_telemetry_init (internal)
> > > Or a different trick in linux/include/rte_os.h could be:
> > > 	typedef void rte_cpuset_t;
> > > so it allows including files, but not using above functions of course.
> > > 
> > Can we just define _GNU_SOURCE in the header file with rte_cpuset_t?
> 
> That would be the simplest solution yes :)
> I don't really like defining such flag in a header file because
> it impacts all code coming after the include.
> It would mean all includes done after DPDK ones behave differently.
> 
> I vote for the trick:
> #ifdef _GNU_SOURCE
> 	typedef cpu_set_t rte_cpuset_t;
> #else
> 	typedef void rte_cpuset_t;
> #endif
> 
> Opinions?

I changed my mind, I think it is saner to not export functions
which use rte_cpuset_t, if the type is not defined.
The type definition is detected thanks to CPU_SETSIZE
and a new definition is used inside DPDK: RTE_HAS_CPUSET.
I think it is more elegant and easier to debug.
I am sending a v6.