bpf: Support replacing cgroup-bpf program in MULTI mode

v3->v4:
- use OPTS_VALID and OPTS_GET to handle bpf_prog_attach_opts.

v2->v3:
- rely on DECLARE_LIBBPF_OPTS from libbpf_common.h;
- separate "required" and "optional" arguments in bpf_prog_attach_xattr;
- convert test_cgroup_attach to prog_tests;
- move the new selftest to prog_tests/cgroup_attach_multi.

v1->v2:
- move DECLARE_LIBBPF_OPTS from libbpf.h to bpf.h (patch 4);
- switch new libbpf API to OPTS framework;
- switch selftest to libbpf OPTS framework.

This patch set adds support for replacing cgroup-bpf programs attached with BPF_F_ALLOW_MULTI flag so that any program in a list can be updated to a new version without service interruption and order of programs can be preserved.

Please see patch 3 for details on the use-case and API changes.

Other patches:
Patch 1 is preliminary refactoring of __cgroup_bpf_attach to simplify it. Patch 2 is minor cleanup of hierarchy_allows_attach.
Patch 4 extends libbpf API to support new set of attach attributes. Patch 5 converts test_cgroup_attach to prog_tests.
Patch 6 adds selftest coverage for the new API.

Andrey Ignatov (6):
bpf: Simplify __cgroup_bpf_attach
bpf: Remove unused new_flags in hierarchy_allows_attach()
bpf: Support replacing cgroup-bpf program in MULTI mode
libbpf: Introduce bpf_prog_attach_xattr selftests/bpf: Convert test_cgroup_attach to prog_tests selftests/bpf: Test BPF_F_REPLACE in cgroup_attach_multi

 include/linux/bpf-cgroup.h                    |   4 +-
 include/uapi/linux/bpf.h                      |  10 +
 kernel/bpf/cgroup.c                           |  97 +--
 kernel/bpf/syscall.c                          |   4 +-
 kernel/cgroup/cgroup.c                        |   5 +-
 tools/include/uapi/linux/bpf.h                |  10 +
 tools/lib/bpf/bpf.c                           |  17 +-
 tools/lib/bpf/bpf.h                           |  11 +
 tools/lib/bpf/libbpf.map                      |   1 +
 tools/testing/selftests/bpf/.gitignore        |   1 -
 tools/testing/selftests/bpf/Makefile          |   3 +-
 .../bpf/prog_tests/cgroup_attach_autodetach.c | 111 ++++
 .../bpf/prog_tests/cgroup_attach_multi.c      | 285 +++++++++
 .../bpf/prog_tests/cgroup_attach_override.c   | 148 +++++
 .../selftests/bpf/test_cgroup_attach.c        | 571 ------------------
 15 files changed, 652 insertions(+), 626 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_attach_autodetach.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_attach_override.c
 delete mode 100644 tools/testing/selftests/bpf/test_cgroup_attach.c

2.17.1