Re: [PATCH v3 bpf-next 0/4] libbpf: deprecate bpf_program__get_prog_info_linear

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

On Mon, Nov 1, 2021 at 3:46 PM Dave Marchevsky <davemarchevsky@fb.com> wrote:
>
> bpf_program__get_prog_info_linear is a helper which wraps the
> bpf_obj_get_info_by_fd BPF syscall with some niceties that put
> all dynamic-length bpf_prog_info in one buffer contiguous with struct
> bpf_prog_info, and simplify the selection of which dynamic data to grab.
>
> The resultant combined struct, bpf_prog_info_linear, is persisted to
> file by 'perf' to enable later annotation of BPF prog data. libbpf
> includes some vaddr <-> offset conversion helpers for
> struct bpf_prog_info_linear to simplify this.
>
> This functionality is heavily tailored to perf's usecase, so its use as
> a general prog info API should be deemphasized in favor of just calling
> bpf_obj_get_info_by_fd, which can be more easily fit to purpose. Some
> examples from caller migrations in this series:
>
>   * Some callers weren't requesting or using dynamic-sized prog info and
>     are well served by a simple get_info_by_fd call (e.g.
>     dump_prog_id_as_func_ptr in bpftool)
>   * Some callers were requesting all of a specific dynamic info type but
>     only using the first record, so can avoid unnecessary malloc by
>     only requesting 1 (e.g. profile_target_name in bpftool)
>   * bpftool's do_dump saves some malloc/free by growing and reusing its
>     dynamic prog_info buf as it loops over progs to grab info and dump.
>
> Perf does need the full functionality of
> bpf_program__get_prog_info_linear and its accompanying structs +
> helpers, so copy the code to its codebase, migrate all other uses in the
> tree, and deprecate the helper in libbpf.
>
> Since the deprecated symbols continue to be included in perf some
> renaming was necessary in perf's copy, otherwise functionality is
> unchanged.
>
> This work was previously discussed in libbpf's issue tracker [0].
>
> [0]: https://github.com/libbpf/libbpf/issues/313
>
> v2->v3:
>   * Remove v2's patch 1 ("libbpf: Migrate internal use of
>     bpf_program__get_prog_info_linear"), which was applied [Andrii]
>   * Add new patch 1 migrating error checking of libbpf calls to
>     new scheme [Andrii, Quentin]
>   * In patch 2, fix != -1 error check of libbpf call, improper realloc
>     handling, and get rid of confusing macros [Andrii]
>   * In patch 4, deprecate starting from 0.6 instead of 0.7 [Andrii]

LGTM. Quentin, can you please take a look and ack as well? Thanks!

>
> v1->v2: fix bpftool do_dump changes to clear bpf_prog_info after use and
> correctly pass realloc'd ptr back (patch 2)
>
> Dave Marchevsky (4):
>   bpftool: Migrate -1 err checks of libbpf fn calls
>   bpftool: use bpf_obj_get_info_by_fd directly
>   perf: pull in bpf_program__get_prog_info_linear
>   libbpf: deprecate bpf_program__get_prog_info_linear
>
>  tools/bpf/bpftool/btf_dumper.c                |  42 +--
>  tools/bpf/bpftool/prog.c                      | 158 ++++++++---
>  tools/bpf/bpftool/struct_ops.c                |   2 +-
>  tools/lib/bpf/libbpf.h                        |   3 +
>  .../Documentation/perf.data-file-format.txt   |   2 +-
>  tools/perf/util/Build                         |   1 +
>  tools/perf/util/annotate.c                    |   3 +-
>  tools/perf/util/bpf-event.c                   |  41 ++-
>  tools/perf/util/bpf-event.h                   |   2 +-
>  tools/perf/util/bpf-utils.c                   | 261 ++++++++++++++++++
>  tools/perf/util/bpf-utils.h                   |  76 +++++
>  tools/perf/util/bpf_counter.c                 |   6 +-
>  tools/perf/util/dso.c                         |   1 +
>  tools/perf/util/env.c                         |   1 +
>  tools/perf/util/header.c                      |  13 +-
>  15 files changed, 527 insertions(+), 85 deletions(-)
>  create mode 100644 tools/perf/util/bpf-utils.c
>  create mode 100644 tools/perf/util/bpf-utils.h
>
> --
> 2.30.2
>