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

[Shahaf Shuler <shahafs@mellanox.com>]

Tuesday, July 24, 2018 2:45 PM, Nélio Laranjeiro:
> 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
> 
> This will force users to re-compile their application to have the missing
> features disabled because some calls are not available, see the list of
> HAVE_RDMA_NLDEV_* elements in the MLX5 makefile due to the issues this
> Netlink stuff brings.

I don't understand. 

First the HAVE_RDMA_NLDEV_* actually re-define the needed enum in case some of the user space headers are missing.
It is not to disable to support on some features in libmnl.

In the doc patch[1] is state the minimal libmnl version:
"Minimal version for libmnl is **1.0.3**."

This one contains all the needed support for switch rules?
Do we expect that w/ more switch rules we will need more feature from this lib? (not sure, it is only to open the sockets).  

[1] https://patches.dpdk.org/patch/43266/

> 
> > 2. dlopen libmnl just like we do for verbs/mlx5
> 
> You want another glue library.  It won't be for this release in this case, I don't
> have time to write such glue.

Yes I agree the first approach is better (static linkage). 

> 
> > >  else
> > >  _LDLIBS-$(CONFIG_RTE_LIBRTE_MLX5_PMD)       += -lrte_pmd_mlx5 -
> > > libverbs -lmlx5 -lmnl
> > >  endif
> > > --
> > > 2.18.0
> >
> 
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> --
> Nélio Laranjeiro
> 6WIND