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Date:   Wed, 20 Dec 2017 13:52:18 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Roman Gushchin <guro@...com>
Cc:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-team@...com>, <scientist@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [RFC PATCH net-next] tools/bpftool: use version from the kernel
 source tree

On Wed, 20 Dec 2017 20:53:41 +0000, Roman Gushchin wrote:
> On Wed, Dec 20, 2017 at 12:29:21PM -0800, Jakub Kicinski wrote:
> > On Wed, 20 Dec 2017 20:19:43 +0000, Roman Gushchin wrote:  
> > > Bpftool determines it's own version based on the kernel
> > > version, which is picked from the linux/version.h header.
> > > 
> > > It's strange to use the version of the installed kernel
> > > headers, and makes much more sense to use the version
> > > of the actual source tree, where bpftool sources are.
> > > 
> > > This patch adds $(srctree)/usr/include to the list
> > > of include files, which causes bpftool to use the version
> > > from the source tree.
> > > 
> > > Example:
> > > before:
> > > 
> > > $ bpftool version
> > > bpftool v4.14.6
> > > 
> > > after:
> > > $ bpftool version
> > > bpftool v4.15.0  
> > 
> > Thanks for the patch, this would indeed use some improvement.
> > 
> > How about we just run make to get the version like liblockdep does?
> > 
> > LIBLOCKDEP_VERSION=$(shell make --no-print-directory -sC ../../.. kernelversion)
> > 
> > probably s@...../..@$(srctree)@
> > 
> > $(srctree)/usr/include is not going to be there for out-of-source builds.  
> 
> Hm, why it's better? It's not only about the kernel version,
> IMO it's generally better to use includes from the source tree,
> rather then system-wide installed kernel headers.

Right I agree the kernel headers are preferred.  I'm not entirely sure
why we don't use them, if it was OK to assume usr/ is there we wouldn't
need the tools/include/uapi/ contraption.  Maybe Arnaldo could explain?

> I've got about out-of-source builds, but do we support it in general?
> How can I build bpftool outside of the kernel tree?
> I've tried a bit, but failed.

This is what I do:

make -C tools/bpf/bpftool/ W=1 O=/tmp/builds/bpftool

> > > diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> > > index 9c089cfa5f3f..6864d416c49e 100644
> > > --- a/tools/bpf/bpftool/Makefile
> > > +++ b/tools/bpf/bpftool/Makefile
> > > @@ -37,7 +37,9 @@ CC = gcc
> > >  
> > >  CFLAGS += -O2
> > >  CFLAGS += -W -Wall -Wextra -Wno-unused-parameter -Wshadow
> > > -CFLAGS += -D__EXPORTED_HEADERS__ -I$(srctree)/tools/include/uapi -I$(srctree)/> > > tools/include -I$(srctree)/tools/lib/bpf -I$(srctree)/kernel/bpf/
> > > +CFLAGS += -D__EXPORTED_HEADERS__ -I$(srctree)/tools/include/uapi
> > > +CFLAGS += -I$(srctree)/tools/include -I$(srctree)/tools/lib/bpf
> > > +CFLAGS += -I$(srctree)/kernel/bpf/ -I$(srctree)/usr/include
> > >  LIBS = -lelf -lbfd -lopcodes $(LIBBPF)
> > >  
> > >  INSTALL ?= install

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