Re: [dpdk-dev] [PATCH v10 1/1] net/af_xdp: introduce AF XDP PMD driver

[Ye Xiaolong <xiaolong.ye@intel.com>]

Hi, Luca

On 04/03, Luca Boccassi wrote:
>On Wed, 2019-04-03 at 18:44 +0100, Ferruh Yigit wrote:
>> On 4/3/2019 5:59 PM, Xiaolong Ye wrote:
>> > Add a new PMD driver for AF_XDP which is a proposed faster version
>> > of
>> > AF_PACKET interface in Linux. More info about AF_XDP, please refer
>> > to [1]
>> > [2].
>> > 
>> > This is the vanilla version PMD which just uses a raw buffer
>> > registered as
>> > the umem.
>> > 
>> > [1] 
>> > https://fosdem.org/2018/schedule/event/af_xdp/
>> > 
>> > [2] 
>> > https://lwn.net/Articles/745934/
>> > 
>> > 
>> > Signed-off-by: Xiaolong Ye <
>> > xiaolong.ye@intel.com
>> > >
>> 
>> I am not able to test functionality but code looks good to me, I can
>> compile via
>> Makefile (with suggested steps in doc) but not able to build with
>> meson, can you
>> please check below comments?
>> 
>> <...>
>> 
>> > @@ -0,0 +1,21 @@
>> > +# SPDX-License-Identifier: BSD-3-Clause
>> > +# Copyright(c) 2019 Intel Corporation
>> > +
>> > +if host_machine.system() != 'linux'
>> > +	build = false
>> > +endif
>> 
>> After this point, if build is false it shouldn't continue to below
>> checks I think.
>> 
>> > +
>> > +bpf_dep = dependency('libbpf', required: false)
>> 
>> My library is in '/usr/local/lib64/libbpf.so' but this line can't
>> find it. Where
>> does 'dependency()' checks for libraries?
>
>dependency() uses only pkg-config (or cmake or embedded specific tools,
>neither of which applies to bpf), so if you haven't built from bpf-next 
>you won't have the pkg-config file installed, and it will fall back to
>the next block.
>
>Side note, there's an issue open upstream in Meson to merge
>dependency() and find_library(), with some traction but it's not done
>yet.
>
>For me building from bpf-next it works fine:
>
>$ PKG_CONFIG_PATH=/tmp/bpf/lib64/pkgconfig/ ninja -C build-gcc-shared
>...
>Dependency libbpf found: YES 0.0.2
>...
>$ lddtree build-gcc-shared/drivers/librte_pmd_af_xdp.so.1.1 
>librte_pmd_af_xdp.so.1.1 => build-gcc-shared/drivers/librte_pmd_af_xdp.so.1.1 (interpreter => none)
>    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6
>    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2
>    libnuma.so.1 => /lib/x86_64-linux-gnu/libnuma.so.1
>    librte_ethdev.so.12 => build-gcc-shared/drivers/../lib/librte_ethdev.so.12
>    librte_eal.so.10 => build-gcc-shared/drivers/../lib/librte_eal.so.10
>    librte_kvargs.so.1 => build-gcc-shared/drivers/../lib/librte_kvargs.so.1
>    librte_net.so.1 => build-gcc-shared/drivers/../lib/librte_net.so.1
>    librte_mbuf.so.5 => build-gcc-shared/drivers/../lib/librte_mbuf.so.5
>    librte_mempool.so.5 => build-gcc-shared/drivers/../lib/librte_mempool.so.5
>    librte_ring.so.2 => build-gcc-shared/drivers/../lib/librte_ring.so.2
>    librte_cmdline.so.2 => build-gcc-shared/drivers/../lib/librte_cmdline.so.2
>    librte_meter.so.2 => build-gcc-shared/drivers/../lib/librte_meter.so.2
>    librte_bus_pci.so.2 => not found
>    librte_pci.so.1 => build-gcc-shared/drivers/../lib/librte_pci.so.1
>    librte_bus_vdev.so.2 => not found
>    libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0
>        librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1
>    libbpf.so.0 => /tmp/bpf/lib64/libbpf.so.0
>        libelf.so.1 => /lib/x86_64-linux-gnu/libelf.so.1
>            libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1
>    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0
>    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6
>    ld-linux-x86-64.so.2 => /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
>
>> > +if bpf_dep.found()
>> > +	build = true
>> > +else
>> > +	bpf_dep = cc.find_library('libbpf', required: false)
>> 
>> Also this line can't find it, in log it says "(tried pkgconfig and
>> cmake)" and
>> yes there is no pkgconfig for it, any idea how 'cmake' used?
>
>The issue here is that it should be cc.find_library('bpf' - not
>'libbpf'. I missed this when reviewing, good catch.
>
>That's because find_library just does a compilation test passing the
>value to the compiler as a linker flag - so right now it's passing
>-llibbpf. Fixing this line and the header line below makes it work
>without pkg-config:
>
>$ CPPFLAGS=-I/tmp/bpf/include LDFLAGS=-L/tmp/bpf/lib64 meson testt
>...
>Dependency libbpf found: NO (tried pkgconfig and cmake)
>Library bpf found: YES

After apply the fix in af_xdp pmd's meson.build, now I was able to build
library for af_xdp pmd.

$ ls drivers/ |grep xdp
a715181@@rte_pmd_af_xdp@sha
a715181@@rte_pmd_af_xdp@sta
a715181@@tmp_rte_pmd_af_xdp@sta
librte_pmd_af_xdp.a
librte_pmd_af_xdp.so
librte_pmd_af_xdp.so.1
librte_pmd_af_xdp.so.1.1
libtmp_rte_pmd_af_xdp.a
rte_pmd_af_xdp.pmd.c

But I found that if I install libbpf to /usr/local/lib64 by default, application
built by meson build will fail to run:

$ ./dpdk-testpmd
./dpdk-testpmd: error while loading shared libraries: libbpf.so.0: cannot open shared object file: No such file or directory

While install libbpf to /usr/lib doesn't have this issue (I was testing on ubuntu system).
Is it a expected behavior? Do we need any fix for it?

Thanks,
Xiaolong
>
>> > +	if bpf_dep.found() and cc.has_header('xsk.h', dependencies:
>> > bpf_dep) and cc.has_header('linux/if_xdp.h')
>> 
>> Should this be 'lib/xsk.h' now?
>
>Yes, this should be 'bpf/xsk.h'
>
>-- 
>Kind regards,
>Luca Boccassi