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

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

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.
If it can't be merged, dependent patches for net/pcap on Windows
can be easily adjusted to work without it.