This series adds support for atomically replacing the XDP program loaded on an
interface. This is achieved by means of a new netlink attribute that can specify
the expected previous program to replace on the interface. If set, the kernel
will compare this "expected fd" attribute with the program currently loaded on
the interface, and reject the operation if it does not match.

With this primitive, userspace applications can avoid stepping on each other's
toes when simultaneously updating the loaded XDP program.

Changelog:

v2:
- Fix checkpatch nits and add .strict_start_type to netlink policy (Jakub)

---

Toke Høiland-Jørgensen (4):
      xdp: Support specifying expected existing program when attaching XDP
      tools: Add EXPECTED_FD-related definitions in if_link.h
      libbpf: Add function to set link XDP fd while specifying old fd
      selftests/bpf: Add tests for attaching XDP programs


 include/linux/netdevice.h                          |  2 +-
 include/uapi/linux/if_link.h                       |  4 +-
 net/core/dev.c                                     | 26 ++++++++--
 net/core/rtnetlink.c                               | 13 +++++
 tools/include/uapi/linux/if_link.h                 |  4 +-
 tools/lib/bpf/libbpf.h                             |  2 +
 tools/lib/bpf/libbpf.map                           |  1 +
 tools/lib/bpf/netlink.c                            | 22 ++++++++-
 .../testing/selftests/bpf/prog_tests/xdp_attach.c  | 55 ++++++++++++++++++++++
 9 files changed, 120 insertions(+), 9 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_attach.c