netdev - Re: [PATCHv2 iproute2-next 0/5] iproute2: add libbpf support

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Date:   Thu, 29 Oct 2020 18:26:56 +0800
From:   Hangbin Liu <haliu@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        David Miller <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Jiri Benc <jbenc@...hat.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCHv2 iproute2-next 0/5] iproute2: add libbpf support

On Wed, Oct 28, 2020 at 09:00:41PM -0600, David Ahern wrote:
> >> nope. you need to be able to handle this. Ubuntu 20.10 was just
> >> released, and it has a version of libbpf. If you are going to integrate
> >> libbpf into other packages like iproute2, it needs to just work with
> >> that version.
> > 
> > OK, I can replace bpf_program__section_name by bpf_program__title().
> 
> I believe this one can be handled through a compatability check. Looks
> the rename / deprecation is fairly recent (78cdb58bdf15f from Sept 2020).

Hi David,

I just come up with another way. In configure, build a temp program and update
the function checking every time is not graceful. How about just check the
libbpf version, since libbpf has exported all functions in src/libbpf.map.

Currently, only bpf_program__section_name() is added in 0.2.0, all other
needed functions are supported in 0.1.0.

So in configure, the new check would like:

check_force_libbpf()
{
    # if set FORCE_LIBBPF but no libbpf support, just exist the config
    # process to make sure we don't build without libbpf.
    if [ -n "$FORCE_LIBBPF" ]; then
        echo "FORCE_LIBBPF set, but couldn't find a usable libbpf"
        exit 1
    fi
}

check_libbpf()
{
    if ! ${PKG_CONFIG} libbpf --exists && [ -z "$LIBBPF_DIR" ] ; then
        echo "no"
        check_force_libbpf
        return
    fi

    if [ $(uname -m) == x86_64 ]; then
        local LIBSUBDIR=lib64
    else
        local LIBSUBDIR=lib
    fi

    if [ -n "$LIBBPF_DIR" ]; then
        LIBBPF_CFLAGS="-I${LIBBPF_DIR}/include -L${LIBBPF_DIR}/${LIBSUBDIR}"
        LIBBPF_LDLIBS="${LIBBPF_DIR}/${LIBSUBDIR}/libbpf.a -lz -lelf"
    else
        LIBBPF_CFLAGS=$(${PKG_CONFIG} libbpf --cflags)
        LIBBPF_LDLIBS=$(${PKG_CONFIG} libbpf --libs)
    fi

    if ${PKG_CONFIG} libbpf --atleast-version 0.1.0 || \
        PKG_CONFIG_LIBDIR=${LIBBPF_DIR}/${LIBSUBDIR}/pkgconfig \
	${PKG_CONFIG} libbpf --atleast-version 0.1.0; then
        echo "HAVE_LIBBPF:=y" >>$CONFIG
        echo 'CFLAGS += -DHAVE_LIBBPF ' $LIBBPF_CFLAGS >> $CONFIG
        echo 'LDLIBS += ' $LIBBPF_LDLIBS >>$CONFIG
        echo "yes"
    else
        echo "no"
        check_force_libbpf
	return
    fi

    # bpf_program__title() is deprecated since libbpf 0.2.0, use
    # bpf_program__section_name() instead if we support
    if ${PKG_CONFIG} libbpf --atleast-version 0.2.0 || \
        PKG_CONFIG_LIBDIR=${LIBBPF_DIR}/${LIBSUBDIR}/pkgconfig \
	${PKG_CONFIG} libbpf --atleast-version 0.2.0; then
        echo 'CFLAGS += -DHAVE_LIBBPF_SECTION_NAME ' $LIBBPF_CFLAGS >> $CONFIG
    fi
}

And in lib/bpf_libbpf.c, we add a new helper like:

static const char *get_bpf_program__section_name(const struct bpf_program *prog)
{
#ifdef HAVE_LIBBPF_SECTION_NAME
	return bpf_program__section_name(prog);
#else
	return bpf_program__title(prog, false);
#endif
}

Thanks
Hangbin