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Date: Wed, 3 Apr 2024 16:41:43 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Luca Boccassi <bluca@debian.org>
Cc: dev@dpdk.org
Subject: Re: [PATCH v5 7/8] net/tap: use libbpf to load new BPF program
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On Wed, 3 Apr 2024 22:19:20 +0100
Luca Boccassi <bluca@debian.org> wrote:

> On Wed, 3 Apr 2024 at 16:55, Stephen Hemminger
> <stephen@networkplumber.org> wrote:
> >
> > On Wed, 03 Apr 2024 12:50:35 +0100
> > Luca Boccassi <bluca@debian.org> wrote:
> >  
> > > Using bpftool to generate the header at build time is a bit icky,
> > > because it will look at sysfs on the build system, which is from the
> > > running kernel. But a build system's kernel might be some ancient LTS,
> > > and even be a completely different kconfig/build/distro from the actual
> > > runtime one.  
> >
> > One other option would be to ship a pre-built skeleton file.
> > Which is what the method the old code did.
> > But that creates an implied dependency on the developers machine build environment.  
> 
> That's what the distro-provided vmlinux.h should help with - by
> #include'ing that, it should be possible to build a co-re bpf program,
> no other artifacts needed. You can try it out locally by generating it
> from the local running kernel on your dev machine:
> 
> bpftool btf dump file /sys/kernel/btf/vmlinux format c > vmlinux.h

Not all distros are providing vmlinux.h.
And some like Ubuntu haven't figured out how to package bpftool and libbpf correctly.