Re: [RFC bpf-next 4/5] iproute2: Allow compiling against libbpf

On 8/22/19 12:43 PM, Toke Høiland-Jørgensen wrote:

Daniel Borkmann [off-list ref] writes:

quoted

On 8/20/19 1:47 PM, Toke Høiland-Jørgensen wrote:

quoted

This adds a configure check for libbpf and renames functions to allow
lib/bpf.c to be compiled with it present. This makes it possible to
port functionality piecemeal to use libbpf.

Signed-off-by: Toke Høiland-Jørgensen <redacted>
---
   configure          | 16 ++++++++++++++++
   include/bpf_util.h |  6 +++---
   ip/ipvrf.c         |  4 ++--
   lib/bpf.c          | 33 +++++++++++++++++++--------------
   4 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/configure b/configure
index 45fcffb6..5a89ee9f 100755
--- a/configure
+++ b/configure

@@ -238,6 +238,19 @@ check_elf()
       fi
   }
   
+check_libbpf()
+{
+    if ${PKG_CONFIG} libbpf --exists; then
+	echo "HAVE_LIBBPF:=y" >>$CONFIG
+	echo "yes"
+
+	echo 'CFLAGS += -DHAVE_LIBBPF' `${PKG_CONFIG} libbpf --cflags` >> $CONFIG
+	echo 'LDLIBS += ' `${PKG_CONFIG} libbpf --libs` >>$CONFIG
+    else
+	echo "no"
+    fi
+}
+
   check_selinux()

More of an implementation detail at this point in time, but want to
make sure this doesn't get missed along the way: as discussed at
bpfconf [0] best for iproute2 to handle libbpf support would be the
same way of integration as pahole does, that is, to integrate it via
submodule [1] to allow kernel and libbpf features to be in sync with
iproute2 releases and therefore easily consume extensions we're adding
to libbpf to aide iproute2 integration.

I can sorta see the point wrt keeping in sync with kernel features. But
how will this work with distros that package libbpf as a regular
library? Have you guys given up on regular library symbol versioning for
libbpf?

Not at all, and I hope you know that. ;-) The reason I added lib/bpf.c
integration into iproute2 directly back then was exactly such that users
can start consuming BPF for tc and XDP via iproute2 /everywhere/ with
only a simple libelf dependency which is also available on all distros
since pretty much forever. If it was an external library, we could have
waited till hell freezes over and initial distro adoption would have pretty
much taken forever: to pick one random example here wrt the pace of some
downstream distros [0]. The main rationale is pretty much the same as with
added kernel features that land complementary iproute2 patches for that
kernel release and as libbpf is developed alongside it is reasonable to
guarantee user expectations that iproute2 released for kernel version x
can make use of BPF features added to kernel x with same loader support
from x.

   [0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1774815

quoted

    [0] http://vger.kernel.org/bpfconf2019.html#session-4

Thanks for that link! Didn't manage to find any of the previous
discussions on iproute2 compatibility.

-Toke