Re: [PATCH 05/18] bpf-preload: Generate static variables

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Mon, Mar 28, 2022 at 10:52 AM Roberto Sassu <roberto.sassu@huawei.com> wrote:
>
> The first part of the preload code generation consists in generating the
> static variables to be used by the code itself: the links and maps to be
> pinned, and the skeleton. Generation of the preload variables and methods
> is enabled with the option -P added to 'bpftool gen skeleton'.
>
> The existing variables maps_link and progs_links in bpf_preload_kern.c have
> been renamed respectively to dump_bpf_map_link and dump_bpf_prog_link, to
> match the name of the variables in the main structure of the light
> skeleton.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>  kernel/bpf/preload/bpf_preload_kern.c         |  35 +-
>  kernel/bpf/preload/iterators/Makefile         |   2 +-
>  .../bpf/preload/iterators/iterators.lskel.h   | 378 +++++++++---------
>  .../bpf/bpftool/Documentation/bpftool-gen.rst |   5 +
>  tools/bpf/bpftool/bash-completion/bpftool     |   2 +-
>  tools/bpf/bpftool/gen.c                       |  27 ++
>  tools/bpf/bpftool/main.c                      |   7 +-
>  tools/bpf/bpftool/main.h                      |   1 +
>  8 files changed, 254 insertions(+), 203 deletions(-)
>

[...]

> +__attribute__((unused)) static void
> +iterators_bpf__assert(struct iterators_bpf *s)
> +{
> +#ifdef __cplusplus
> +#define _Static_assert static_assert
> +#endif
> +#ifdef __cplusplus
> +#undef _Static_assert
> +#endif
> +}
> +
> +static struct bpf_link *dump_bpf_map_link;
> +static struct bpf_link *dump_bpf_prog_link;
> +static struct iterators_bpf *skel;

I don't understand what is this and what for? You are making an
assumption that light skeleton can be instantiated just once, why? And
adding extra bpftool option to light skeleton codegen just to save a
bit of typing at the place where light skeleton is actually
instantiated and used doesn't seems like a right approach.

Further, even if this is the way to go, please split out bpftool
changes from kernel changes. There is nothing requiring them to be
coupled together.

[...]