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

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

[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?
---
 config/meson.build | 1 -
 1 file changed, 1 deletion(-)

diff --git a/config/meson.build b/config/meson.build
index 66a2edcc47..95777cf331 100644
--- a/config/meson.build
+++ b/config/meson.build
@@ -183,7 +183,6 @@ if not pcap_dep.found()
 endif
 if pcap_dep.found() and cc.has_header('pcap.h', dependencies: pcap_dep)
 	dpdk_conf.set('RTE_PORT_PCAP', 1)
-	dpdk_extra_ldflags += '-lpcap'
 endif
 
 # for clang 32-bit compiles we need libatomic for 64-bit atomic ops
-- 
2.31.1

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

[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?

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

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

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

[Thomas Monjalon]

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.

In the meantime, we could document why this line is required.

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

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

[Stephen Hemminger]

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.