Re: [RFC bpf-next 0/5] Convert iproute2 to use libbpf (WIP)

On Tue, Feb 4, 2020 at 12:25 AM Toke Høiland-Jørgensen [off-list ref] wrote:

Andrii Nakryiko [off-list ref] writes:

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On Mon, Feb 3, 2020 at 8:53 PM David Ahern [off-list ref] wrote:

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On 2/3/20 8:41 PM, Andrii Nakryiko wrote:

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On Mon, Feb 3, 2020 at 5:46 PM David Ahern [off-list ref] wrote:

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On 2/3/20 5:56 PM, Andrii Nakryiko wrote:

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Great! Just to disambiguate and make sure we are in agreement, my hope
here is that iproute2 can completely delegate to libbpf all the ELF

iproute2 needs to compile and continue working as is when libbpf is not
available. e.g., add check in configure to define HAVE_LIBBPF and move
the existing code and move under else branch.

Wouldn't it be better to statically compile against libbpf in this
case and get rid a lot of BPF-related code and simplify the rest of
it? This can be easily done by using libbpf through submodule, the
same way as BCC and pahole do it.

iproute2 compiles today and runs on older distributions and older
distributions with newer kernels. That needs to hold true after the move
to libbpf.

And by statically compiling against libbpf, checked out as a
submodule, that will still hold true, wouldn't it? Or there is some
complications I'm missing? Libbpf is designed to handle old kernels
with no problems.

My plan was to use the same configure test I'm using for xdp-tools
(where I in turn copied the structure of the configure script from
iproute2):

https://github.com/xdp-project/xdp-tools/blob/master/configure#L59

This will look for a system libbpf install and compile against it if it
is compatible, and otherwise fall back to a statically linking against a
git submodule.

How will this work when build host has libbpf installed, but target
host doesn't? You'll get dynamic linker error when trying to run that
tool.

If the goal is to have a reliable tool working everywhere, and you
already support having libbpf as a submodule, why not always use
submodule's libbpf? What's the concern? Libbpf is a small library, I
don't think a binary size argument is enough reason to not do this. On
the other hand, by using libbpf from submodule, your tool is built
*and tested* with a well-known libbpf version that tool-producer
controls.

We'll need to double-check that this will work on everything currently
supported by iproute2, and fix libbpf if there are any issues with that.
Not that I foresee any, but you never know :)

-Toke