Re: [dpdk-dev] [PATCH] mk: fix application compilation with lmnl and mlx5

[Shahaf Shuler <shahafs@mellanox.com>]

Tuesday, July 24, 2018 3:56 PM, Adrien Mazarguil:
> Subject: Re: [PATCH] mk: fix application compilation with lmnl and mlx5
> 
> On Tue, Jul 24, 2018 at 11:21:52AM +0000, Shahaf Shuler wrote:
> > Tuesday, July 24, 2018 12:29 PM, Nelio Laranjeiro:
> > > Subject: [PATCH] mk: fix application compilation with lmnl and mlx5
> > >
> > > When Mellanox MLX5 PMD is compiled with
> > > CONFIG_RTE_LIBRTE_MLX5_DLOPEN_DEPS=y, the external dependency
> on
> > > libmln is missing.
> > >
> > > Fixes: 4d5cce06231a ("net/mlx5: lay groundwork for switch offloads")
> > > Cc: adrien.mazarguil@6wind.com
> > >
> > > Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
> > > ---
> > >  mk/rte.app.mk | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mk/rte.app.mk b/mk/rte.app.mk index
> > > f4d28c2da..ff39d37aa
> > > 100644
> > > --- a/mk/rte.app.mk
> > > +++ b/mk/rte.app.mk
> > > @@ -149,7 +149,7 @@ else
> > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_MLX4_PMD)       += -lrte_pmd_mlx4 -
> > > libverbs -lmlx4
> > >  endif
> > >  ifeq ($(CONFIG_RTE_LIBRTE_MLX5_DLOPEN_DEPS),y)
> > > -_LDLIBS-$(CONFIG_RTE_LIBRTE_MLX5_PMD)       += -lrte_pmd_mlx5 -ldl
> > > +_LDLIBS-$(CONFIG_RTE_LIBRTE_MLX5_PMD)       += -lrte_pmd_mlx5 -ldl
> -
> > > lmnl
> >
> > This issue raise some more basic question.
> > The DLOPEN mode was introduced to run in systems which don't have
> verbs/mlx5 libs installed, because those were the only dependencies for the
> PMD back then.
> > Now we have the libmnl, which is external dependency just like rdma-core,
> and following your fix, hard linked also in case of DLOPEN option.
> > It means the whole DPDK binary/lib will be depended on libmnl and this is
> not what we want with DLOPEN.
> >
> > Can we consider different options:
> > 1. always statically link libmnl
> > 2. dlopen libmnl just like we do for verbs/mlx5
> 
> Regarding 2, unlike rdma-core/MLNX_OFED, libmnl should be available pretty
> much everywhere iproute2 can be found. The minimal version supported
> (1.0.3) was released in 2012.
> 
> Using the glue approach for such a small library seems overkill; should we
> choose this path, we must also consider to get rid of it entirely since doing so
> would require more glue code than what mlx5 needs from this library.
> 
> So with the current approach, either the application or the PMD inherits a
> dependency to libmnl, depending on whether
> CONFIG_RTE_BUILD_SHARED_LIB is respectively disabled or enabled.
> 
> If disabled, applications that want static linkage can specify -static as part of
> their compilation flags to let the compiler automatically look for libmnl.a as
> needed. 

Can you confirm static compilation w/ libmnl is working w/o any issues? 

To put this in perspective, this also applies to all other dependencies
> it will collect while compiling DPDK (libz, libdl, libpcap, libnuma to name a
> few).
> 
> In my opinion, the purpose of *_DLOPEN_DEPS is to deal with large,
> nonstandard libraries where versioning issues are commonplace. This doesn't
> apply to libmnl, which shouldn't be a maintenance nightmare to package
> maintainers. I suggest to leave things as is.
> 
> --
> Adrien Mazarguil
> 6WIND