netdev - Re: [RFC PATCH net-next] tools/bpftool: use version from the kernel source tree

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Message-ID: <20171221120736.GA7054@castle.DHCP.thefacebook.com>
Date:   Thu, 21 Dec 2017 12:07:42 +0000
From:   Roman Gushchin <guro@...com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.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, Dec 20, 2017 at 01:52:18PM -0800, Jakub Kicinski wrote:
> 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

This works perfectly with my patch:

$ make -C ~/linux/tools/bpf/ W=1 O=/home/guro/build/ --trace
<...>
echo '  CC       '/home/guro/build/main.o;gcc -O2 -W -Wall -Wextra -Wno-unused-parameter -Wshadow -D__EXPORTED_HEADERS__ -I/home/guro/linux/tools/include/uapi -I/home/guro/linux/tools/include -I/home/guro/linux/tools/lib/bpf -I/home/guro/linux/kernel/bpf/ -I/home/guro/linux/usr/include -DNEW_DISSASSEMBLER_SIGNATURE   -c -MMD -o /home/guro/build/main.o main.c
<...>
echo '  LINK     '/home/guro/build/bpftool;gcc -O2 -W -Wall -Wextra -Wno-unused-parameter -Wshadow -D__EXPORTED_HEADERS__ -I/home/guro/linux/tools/include/uapi -I/home/guro/linux/tools/include -I/home/guro/linux/tools/lib/bpf -I/home/guro/linux/kernel/bpf/ -I/home/guro/linux/usr/include -DNEW_DISSASSEMBLER_SIGNATURE -o /home/guro/build/bpftool /home/guro/build/common.o /home/guro/build/cgroup.o /home/guro/build/main.o /home/guro/build/json_writer.o /home/guro/build/prog.o /home/guro/build/map.o /home/guro/build/jit_disasm.o /home/guro/build/disasm.o /home/guro/build/libbpf.a -lelf -lbfd -lopcodes /home/guro/build/libbpf.a
  LINK     /home/guro/build/bpftool
make[1]: Leaving directory '/home/guro/linux/tools/bpf/bpftool'
make: Leaving directory '/home/guro/linux/tools/bpf'

$ ./build/bpftool version
./build/bpftool v4.15.0

Thanks!