[PATCH v3 bpf-next 0/9] libbpf: add bpf_link and tracing attach APIs

[Andrii Nakryiko <andriin@fb.com>]

This patchset adds the following APIs to allow attaching BPF programs to
tracing entities:
- bpf_program__attach_perf_event for attaching to any opened perf event FD,
  allowing users full control;
- bpf_program__attach_kprobe for attaching to kernel probes (both entry and
  return probes);
- bpf_program__attach_uprobe for attaching to user probes (both entry/return);
- bpf_program__attach_tracepoint for attaching to kernel tracepoints;
- bpf_program__attach_raw_tracepoint for attaching to raw kernel tracepoint
  (wrapper around bpf_raw_tracepoint_open);

This set of APIs makes libbpf more useful for tracing applications.

All attach APIs return abstract struct bpf_link that encapsulates logic of
detaching BPF program. See patch #2 for details. bpf_assoc was considered as
an alternative name for this opaque "handle", but bpf_link seems to be
appropriate semantically and is nice and short.

Pre-patch #1 makes internal libbpf_strerror_r helper function work w/ negative
error codes, lifting the burder off callers to keep track of error sign.
Patch #2 adds bpf_link abstraction.
Patch #3 adds attach_perf_event, which is the base for all other APIs.
Patch #4 adds kprobe/uprobe APIs.
Patch #5 adds tracepoint API.
Patch #6 adds raw_tracepoint API.
Patch #7 converts one existing test to use attach_perf_event.
Patch #8 adds new kprobe/uprobe tests.
Patch #9 converts some selftests currently using tracepoint to new APIs.

v2->v3:
- added bpf_link concept (Daniel);
- didn't add generic bpf_link__attach_program for reasons described in [0];
- dropped Stanislav's Reviewed-by from patches #2-#6, in case he doesn't like
  the change;

v1->v2:
- preserve errno before close() call (Stanislav);
- use libbpf_perf_event_disable_and_close in selftest (Stanislav);
- remove unnecessary memset (Stanislav);

[0] https://lore.kernel.org/bpf/CAEf4BzZ7EM5eP2eaZn7T2Yb5QgVRiwAs+epeLR1g01TTx-6m6Q@mail.gmail.com/

Andrii Nakryiko (9):
  libbpf: make libbpf_strerror_r agnostic to sign of error
  libbpf: introduce concept of bpf_link
  libbpf: add ability to attach/detach BPF program to perf event
  libbpf: add kprobe/uprobe attach API
  libbpf: add tracepoint attach API
  libbpf: add raw tracepoint attach API
  selftests/bpf: switch test to new attach_perf_event API
  selftests/bpf: add kprobe/uprobe selftests
  selftests/bpf: convert existing tracepoint tests to new APIs

 tools/lib/bpf/libbpf.c                        | 402 ++++++++++++++++++
 tools/lib/bpf/libbpf.h                        |  21 +
 tools/lib/bpf/libbpf.map                      |   8 +-
 tools/lib/bpf/str_error.c                     |   2 +-
 .../selftests/bpf/prog_tests/attach_probe.c   | 155 +++++++
 .../bpf/prog_tests/stacktrace_build_id.c      |  50 +--
 .../bpf/prog_tests/stacktrace_build_id_nmi.c  |  31 +-
 .../selftests/bpf/prog_tests/stacktrace_map.c |  43 +-
 .../bpf/prog_tests/stacktrace_map_raw_tp.c    |  15 +-
 .../selftests/bpf/progs/test_attach_probe.c   |  55 +++
 10 files changed, 687 insertions(+), 95 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/attach_probe.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_attach_probe.c

-- 
2.17.1