[RFC,bpf-next,0/2] bpf, libbpf: share BTF data show functionality

Message

Alan Maguire Jan. 11, 2021, 5:32 p.m. UTC

The BPF Type Format (BTF) can be used in conjunction with the helper
bpf_snprintf_btf() to display kernel data with type information.

This series generalizes that support and shares it with libbpf so
that libbpf can display typed data.  BTF display functionality is
factored out of kernel/bpf/btf.c into kernel/bpf/btf_show_common.c,
and that file is duplicated in tools/lib/bpf.  Similarly, common
definitions and inline functions needed for this support are
extracted into include/linux/btf_common.h and this header is again
duplicated in tools/lib/bpf.

Patch 1 carries out the refactoring, for which no kernel changes
are intended, and introduces btf__snprintf() a libbpf function
that supports dumping a string representation of typed data using
the struct btf * and id associated with that type.

Patch 2 tests btf__snprintf() with built-in and kernel types to
ensure data is of expected format.  The test closely mirrors
the BPF program associated with the snprintf_btf.c; in this case
however the string representations are verified in userspace rather
than in BPF program context.

Alan Maguire (2):
  bpf: share BTF "show" implementation between kernel and libbpf
  selftests/bpf: test libbpf-based type display

 include/linux/btf.h                                |  121 +-
 include/linux/btf_common.h                         |  286 +++++
 kernel/bpf/Makefile                                |    2 +-
 kernel/bpf/arraymap.c                              |    1 +
 kernel/bpf/bpf_struct_ops.c                        |    1 +
 kernel/bpf/btf.c                                   | 1215 +------------------
 kernel/bpf/btf_show_common.c                       | 1218 ++++++++++++++++++++
 kernel/bpf/core.c                                  |    1 +
 kernel/bpf/hashtab.c                               |    1 +
 kernel/bpf/local_storage.c                         |    1 +
 kernel/bpf/verifier.c                              |    1 +
 kernel/trace/bpf_trace.c                           |    1 +
 tools/lib/bpf/Build                                |    2 +-
 tools/lib/bpf/btf.h                                |    7 +
 tools/lib/bpf/btf_common.h                         |  286 +++++
 tools/lib/bpf/btf_show_common.c                    | 1218 ++++++++++++++++++++
 tools/lib/bpf/libbpf.map                           |    1 +
 .../selftests/bpf/prog_tests/snprintf_btf_user.c   |  192 +++
 18 files changed, 3236 insertions(+), 1319 deletions(-)
 create mode 100644 include/linux/btf_common.h
 create mode 100644 kernel/bpf/btf_show_common.c
 create mode 100644 tools/lib/bpf/btf_common.h
 create mode 100644 tools/lib/bpf/btf_show_common.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf_btf_user.c

Comments

Alexei Starovoitov Jan. 12, 2021, 2:45 a.m. UTC | #1

On Mon, Jan 11, 2021 at 05:32:51PM +0000, Alan Maguire wrote:
> The BPF Type Format (BTF) can be used in conjunction with the helper
> bpf_snprintf_btf() to display kernel data with type information.
> 
> This series generalizes that support and shares it with libbpf so
> that libbpf can display typed data.  BTF display functionality is
> factored out of kernel/bpf/btf.c into kernel/bpf/btf_show_common.c,
> and that file is duplicated in tools/lib/bpf.  Similarly, common
> definitions and inline functions needed for this support are
> extracted into include/linux/btf_common.h and this header is again
> duplicated in tools/lib/bpf.

I think duplication will inevitable cause code to diverge.
Could you keep a single copy?
Take a look at kernel/bpf/disasm.[ch]
It compiled once for the kernel and once for bpftool.
So should be possible to do something similar for this case as well?