bpf/tracing: allow user space to query prog array on the same tp

Commit e87c6bc3852b ("bpf: permit multiple bpf attachments for a single perf event") added support to attach multiple bpf programs to a single perf event. Given a perf event (kprobe, uprobe, or kernel tracepoint), the perf ioctl interface is used to query bpf programs attached to the same trace event.

There already exists a BPF_PROG_QUERY command for introspection currently used by cgroup+bpf. We did have an implementation for querying tracepoint+bpf through the same interface. However, it looks cleaner to use ioctl() style of api here, since attaching bpf prog to tracepoint/kuprobe is also done via ioctl.

Patch #1 had the core implementation and patch #2 added a test case in tools bpf selftests suite.

Changelogs:
v3 -> v4:
- Fix a compilation error with newer gcc like 6.3.1 while old gcc 4.8.5 is okay. I was using &uquery->ids to represent the address to the ids array to make it explicit that the address is passed, and this syntax is rightly rejected by gcc 6.3.1.
v2 -> v3:
- Change uapi structure perf_event_query_bpf to be more clearer based on Peter's suggestion, and adjust other codes accordingly.
v1 -> v2:
- Rebase on top of net-next.
- Use existing bpf_prog_array_length function instead of implementing the same functionality in function bpf_prog_array_copy_info.

Yonghong Song (2):
bpf/tracing: allow user space to query prog array on the same tp bpf/tracing: add a bpf test for new ioctl query interface

 include/linux/bpf.h                           |   4 +
 include/uapi/linux/perf_event.h               |  22 +++++
 kernel/bpf/core.c                             |  21 ++++
 kernel/events/core.c                          |   3 +
 kernel/trace/bpf_trace.c                      |  23 +++++
 tools/include/uapi/linux/perf_event.h         |  22 +++++
 tools/testing/selftests/bpf/Makefile          |   2 +-
 tools/testing/selftests/bpf/test_progs.c      | 134 ++++++++++++++++++++++++++
 tools/testing/selftests/bpf/test_tracepoint.c |  26 +++++
 9 files changed, 256 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/test_tracepoint.c

2.9.5