[PATCH v2 bpf-next 0/5] BPF link force-detach support

[Andrii Nakryiko <andriin@fb.com>]

This patch set adds new BPF link operation, LINK_DETACH, allowing processes
with BPF link FD to force-detach it from respective BPF hook, similarly how
BPF link is auto-detached when such BPF hook (e.g., cgroup, net_device, netns,
etc) is removed. This facility allows admin to forcefully undo BPF link
attachment, while process that created BPF link in the first place is left
intact.

Once force-detached, BPF link stays valid in the kernel as long as there is at
least one FD open against it. It goes into defunct state, just like
auto-detached BPF link.

bpftool also got `link detach` command to allow triggering this in
non-programmatic fashion.

v1->v2:
- improve error reporting in `bpftool link detach` (Song).

Andrii Nakryiko (5):
  bpf: add support for forced LINK_DETACH command
  libbpf: add bpf_link detach APIs
  selftests/bpf: add link detach tests for cgroup, netns, and xdp
    bpf_links
  tools/bpftool: add `link detach` subcommand
  tools/bpftool: add documentation and bash-completion for `link detach`

 include/linux/bpf.h                           |  1 +
 include/uapi/linux/bpf.h                      |  5 ++
 kernel/bpf/cgroup.c                           | 15 +++++-
 kernel/bpf/net_namespace.c                    |  8 +++
 kernel/bpf/syscall.c                          | 26 ++++++++++
 net/core/dev.c                                | 11 +++-
 .../bpftool/Documentation/bpftool-link.rst    |  8 +++
 tools/bpf/bpftool/bash-completion/bpftool     |  4 +-
 tools/bpf/bpftool/link.c                      | 37 +++++++++++++-
 tools/include/uapi/linux/bpf.h                |  5 ++
 tools/lib/bpf/bpf.c                           | 10 ++++
 tools/lib/bpf/bpf.h                           |  2 +
 tools/lib/bpf/libbpf.c                        |  5 ++
 tools/lib/bpf/libbpf.h                        |  1 +
 tools/lib/bpf/libbpf.map                      |  2 +
 .../selftests/bpf/prog_tests/cgroup_link.c    | 20 +++++++-
 .../selftests/bpf/prog_tests/sk_lookup.c      | 51 +++++++++----------
 .../selftests/bpf/prog_tests/xdp_link.c       | 14 +++++
 tools/testing/selftests/bpf/testing_helpers.c | 14 +++++
 tools/testing/selftests/bpf/testing_helpers.h |  3 ++
 20 files changed, 208 insertions(+), 34 deletions(-)

-- 
2.24.1