[Buildroot] [PATCH] package/knock: fix static build with libusb

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Dear Yann E. MORIN,

On Sun, 22 Jun 2014 19:04:56 +0200, Yann E. MORIN wrote:
> From: "Yann E. MORIN" <yann.morin.1998@free.fr>
> 
> knock depends on libpcap, that has an optional dependency on libusb.
> Alas, libpcap does not install a .pc file, so knock does not know
> that it should link with -lusb-1.0.
> 
> When linking dynamically, this is not an issue, since the linker does
> follow the DT_NEEDED tags of libpcap, and thus pulls libusb-1.0 in at
> the same time. And since linusb uses threads, libpthread is pulled in
> as well.
> 
> However, when linking statically, all of this fails.
> 
> Fix that by telling knock's ./configure what libraries to link with
> when doing a static build and libusb is enabled.
> 
> Fixes:
>     http://autobuild.buildroot.net/results/1eb/1eb877ebd9469c9261bf114fc7733819ae3fd562/
> 
> Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
> Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
> ---
>  package/knock/knock.mk | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/package/knock/knock.mk b/package/knock/knock.mk
> index 8d2b41e..ace23fa 100644
> --- a/package/knock/knock.mk
> +++ b/package/knock/knock.mk
> @@ -10,4 +10,8 @@ KNOCK_LICENSE = GPLv2+
>  KNOCK_LICENSE_FILES = COPYING
>  KNOCK_DEPENDENCIES = libpcap
>  
> +ifeq ($(BR2_PREFER_STATIC_LIB)$(BR2_PACKAGE_LIBUSB),yy)
> +KNOCK_CONF_OPT = LIBS="-lusb-1.0 -pthread"
> +endif

Thanks. However, I've already stated that before, but I continue to
wonder if this is the right way to fix this. Shouldn't we instead fix
libcap by adding a .pc file and submit that upstream, instead of adding
more and more LIBS="-lblah" all over the place? Of course, that's not
a comment targeted specifically at your patch (we're doing the same
thing for many other packages), but I'm wondering if that's the right
thing to do.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com