[Buildroot] [PATCH] netsnmp: fix libnl include path in configure script

[Julien Floret]

Hello Thomas,

> The right fix is to modify configure.d/config_os_libs2 to avoid passing
> -I/usr/include/libnl3, and then autoreconf the package. To do this, you
> have a few options:
>
>  - Remove -I/usr/include/libnl3 entirely, and assume the user will pass
>    the appropriate options in CPPFLAGS.
>
>  - Use -I=/usr/include/libnl3, gcc will automatically replace = by the
>    compiler sysroot. However, I have no idea whether this also works
>    with non-gcc compilers.
>
>  - Change the --with-nl option so that it takes a path to the nl
>    library.

Thanks for your analysis. Indeed, your proposals are much better than
patching the configure script on the fly ;)

In fact, I just saw that the issue has been addressed upstream:
libnl include paths & libs can now be overriden with configure environment
variables:
https://sourceforge.net/p/net-snmp/code/ci/852dcd644cfe4cfc7177649eaec163d6221f2be1/

So if you're ok with this, I suggest to:
- embed the upstream patch in package/netsnmp/
- trigger an autoreconf
- pass the right LIBNL3_{CFLAGS,LIBS} variables in NETSNMP_CONF_ENV.

> Also, if netsnmp optionally uses libnl, then it should optionally
> depend on it. Something like:
>
> ifeq ($(BR2_PACKAGE_LIBNL),y)
> NETSNMP_DEPENDENCIES += libnl
> NETSNMP_CONF_OPTS += --with-nl
> else
> NETSNMP_CONF_OPTS += --without-nl
> endif

OK, I will add this as well.

> Or, if you don't care about libnl support in netsnmp and don't want to
> spend time fixing the problem, just add --without-nl to netsnmp
> configuration options.