Re: [dpdk-dev] [PATCH v5] build: remove redundant libpcap link

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 14 Apr 2021 23:10:46 +0200
Thomas Monjalon <thomas@monjalon.net> wrote:

> 14/04/2021 23:02, Dmitry Kozlyuk:
> > 2021-04-14 11:41 (UTC+0200), Thomas Monjalon:  
> > > 09/04/2021 14:25, Thomas Monjalon:  
> > > > From: Gabriel Ganne <gabriel.ganne@6wind.com>
> > > > 
> > > > The pcap PMD and the librte_port both declare their dependency to libpcap
> > > > with a line "ext_deps += pcap_dep".
> > > > Then meson automatically adds this dependency to the pkg-config file
> > > > in the "Requires.private" section for static builds.
> > > > 
> > > > The additional update of dpdk_extra_ldflags was adding the dependency
> > > > in the "Libs.private" section of the pkg-config, that is unnecessary.
> > > > 
> > > > Fixes: efd5d1a8d8dd ("drivers/net: build some vdev PMDs with meson")
> > > > Fixes: 268fa581b1ff ("port: fix pcap support with meson")
> > > > Cc: stable@dpdk.org
> > > > 
> > > > Signed-off-by: Gabriel Ganne <gabriel.ganne@6wind.com>
> > > > Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> > > > ---
> > > > I have a doubt whether this option is really always useless.
> > > > In the case of an old pcap (<1.9) without pkg-config support,
> > > > and with the minimum meson supported (0.47.1),
> > > > are we sure the generated pkg-config file will include -lpcap?    
> > > 
> > > Any volunteer to test please?  
> > 
> > Ubuntu 16.04, Meson 0.47.1, libpcap 1.7.4-2ubuntu0.1, after the patch
> > libdpdk.pc contains:
> > 
> > 	Libs.private: -lpcap -lpcap -lpcap -lpcap -lpcap -lpcap -lpcap -lpcap
> > 	-lpcap -lpcap [...DPDK libraries...]
> > 
> > Note that -lpcap comes _before_ DPDK libraries that require it.
> > As a consequence, this doesn't link with unresolved libpcap symbols:
> > 
> > 	gcc test.c `pkg-config --static --cflags --libs libdpdk`
> > 
> > Before the patch -lpcap was _after_ DPDK libraries,
> > link succeeded (there was also _one_ -lpcap before DPDK libraries).
> > 
> > Meson 0.55.1 places -lpcap _after_ DPDK libraries,
> > link succeeds both before and after the patch.
> > 
> > Conclusion: this patch really breaks .pc file for older meson.  
> 
> Thanks for the test.
> I propose to defer this patch.
> It could be merged when we upgrade meson requirement.

Current documented meson requirement is:
	Version 0.53.2 or later of meson is required

So this patch should be considered.