Re: [PATCH v3 bpf-next 0/2] libbpf: capability for resizing datasec maps

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

On Tue, May 23, 2023 at 5:45 PM JP Kobryn <inwardvessel@gmail.com> wrote:
>
> Due to the way the datasec maps like bss, data, rodata are memory
> mapped, they cannot be resized with bpf_map__set_value_size() like
> non-datasec maps can. This series offers a way to allow the resizing of
> datasec maps, by having the mapped regions resized as needed and also
> adjusting associated BTF info if possible.
>
> The thought behind this is to allow for use cases where a given datasec
> needs to scale to for example the number of CPU's present. A bpf program
> can have a global array in a data section with an initial length and
> before loading the bpf program, the array length could be extended to
> match the CPU count. The selftests included in this series perform this
> scaling to an arbitrary value to demonstrate how it can work.
>
> JP Kobryn (2):
>   add capability for resizing datasec maps
>   selftests for resizing datasec maps
>
>  tools/lib/bpf/libbpf.c                        | 130 ++++++++++
>  tools/lib/bpf/libbpf.h                        |  17 +-
>  .../bpf/prog_tests/global_map_resize.c        | 236 ++++++++++++++++++
>  .../bpf/progs/test_global_map_resize.c        |  58 +++++
>  4 files changed, 440 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/global_map_resize.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_global_map_resize.c
>
> --
> 2.40.0
>

Thanks, it's a great feature! I did some formatting and cosmetic
adjustments before applying. I also rolled into the first patch a
change to make bpf_map__initial_value() return non-const pointer, as
const pointer doesn't make much sense (this is backwards compatible
change). Applied to bpf-next, thanks!