Re: [dpdk-dev] [PATCH v9 1/1] net/af_xdp: introduce AF XDP PMD driver

[Luca Boccassi <bluca@debian.org>]

On Wed, 2019-04-03 at 11:36 +0100, Luca Boccassi wrote:
> On Wed, 2019-04-03 at 17:59 +0800, Ye Xiaolong wrote:
> > Hi, Luca
> > 
> > On 04/02, Luca Boccassi wrote:
> > > On Tue, 2019-04-02 at 23:46 +0800, Xiaolong Ye wrote:
> > > > diff --git a/drivers/net/af_xdp/Makefile
> > > > b/drivers/net/af_xdp/Makefile
> > > > new file mode 100644
> > > > index 000000000..8343e3016
> > > > --- /dev/null
> > > > +++ b/drivers/net/af_xdp/Makefile
> > > > @@ -0,0 +1,32 @@
> > > > +# SPDX-License-Identifier: BSD-3-Clause
> > > > +# Copyright(c) 2019 Intel Corporation
> > > > +
> > > > +include $(RTE_SDK)/mk/rte.vars.mk
> > > > +
> > > > +#
> > > > +# library name
> > > > +#
> > > > +LIB = librte_pmd_af_xdp.a
> > > > +
> > > > +EXPORT_MAP := rte_pmd_af_xdp_version.map
> > > > +
> > > > +LIBABIVER := 1
> > > > +
> > > > +CFLAGS += -O3
> > > > +
> > > > +# require kernel version >= v5.1-rc1
> > > > +CFLAGS += -I$(RTE_KERNELDIR)/tools/include
> > > > +CFLAGS += -I$(RTE_KERNELDIR)/tools/lib/bpf
> > > 
> > > Sorry for not noticing this before, but doesn't this require the
> > > full
> > > kernel tree rather than just the typical headers package?
> > > Requiring
> > > the
> > > full kernel tree to be available at build time will make this
> > > unbuildable on distros that still use makefiles, like RHEL and
> > > SUSE. At
> > > least on Debian and Ubuntu, the kernel headers packages
> > > distributed
> > > do
> > > not include the full kernel tree, only the headers, so there's no
> > > tools/lib or tools/include.
> > 
> > Currently we do have dependencies on the kernel src tree, as xsk.h
> > and
> > asm/barrier wouldn't be installed by libbpf, so before libbpf
> > handles
> > these
> > properly, can we keep the current RTE_KERNELDIR in Makefile for
> > now,
> > and mention
> > the dependencies in document, also suggest users to config
> > RTE_KERNELDIR to correct
> > kernel src tree if they want to use af_xdp pmd?
> > 
> > Something like:
> > 
> > dependencies:
> > - kernel source code (>= v5.1-rc1)
> > - build libbfp and install
> > 
> > Thanks,
> > Xiaolong
> 
> asm/barrier.h is installed by the kernel headers packages so it would
> be fine (although not ideal) and not need the full source tree.
> xsk.h is a bit more worrying, as it looks like an internal header
> from
> here.
> 
> Is it really necessary for external applications to use an internal-
> only header and a kernel header to be able to use libbpf?

Actually, xsk.h is now installed by the library makefile:

https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=379e2014c95b

So the full kernel source tree is no longer required.

Is asm/barrier.h really required? Isn't there an userspace alternative?

Also, the license in asm/barrier.h is GPL-2.0 only. It is not a
userspace header so it is not covered by the userspace exception, which
means at the very least the af_xdp PMD shared object is also licensed
under GPL-2.0 only, isn't it?

-- 
Kind regards,
Luca Boccassi