bpf: Add bpf_link support for sk_msg and sk_skb progs

One of our internal services started to use sk_msg program and currently
it used existing prog attach/detach2 as demonstrated in selftests.
But attach/detach of all other bpf programs are based on bpf_link.
Consistent attach/detach APIs for all programs will make things easy to
undersand and less error prone. So this patch added bpf_link
support for BPF_PROG_TYPE_SK_MSG. Based on comments from
previous RFC patch, I added BPF_PROG_TYPE_SK_SKB support as well
as both program types have similar treatment w.r.t. bpf_link
handling.

For the patch series, patch 1 added kernel support. Patch 2
added libbpf support. Patch 3 added bpftool support and
patches 4/5 added some new tests.

Changelogs:
  v4 -> v5:
    - increase scope of mutex protection in link_release.
    - remove previous-leftover entry in libbpf.map.
    - make some code changes for better understanding.
  v3 -> v4:
    - use a single mutex lock to protect both attach/detach/update
      and release/fill_info/show_fdinfo.
    - simplify code for sock_map_link_lookup().
    - fix a few bugs.
    - add more tests.
  v2 -> v3:
    - consolidate link types of sk_msg and sk_skb to
      a single link type BPF_PROG_TYPE_SOCKMAP.
    - fix bpf_link lifecycle issue. in v2, after bpf_link
      is attached, a subsequent prog_attach could change
      that bpf_link. this patch makes bpf_link having
      correct behavior such that it won't go away facing
      other prog/link attach for the same map and the same
      attach type.

Yonghong Song (5):
  bpf: Add bpf_link support for sk_msg and sk_skb progs
  libbpf: Add bpf_link support for BPF_PROG_TYPE_SOCKMAP
  bpftool: Add link dump support for BPF_LINK_TYPE_SOCKMAP
  selftests/bpf: Refactor out helper functions for a few tests
  selftests/bpf: Add some tests with new bpf_program__attach_sockmap()
    APIs

 include/linux/bpf.h                           |   6 +
 include/linux/skmsg.h                         |   4 +
 include/uapi/linux/bpf.h                      |   5 +
 kernel/bpf/syscall.c                          |   4 +
 net/core/sock_map.c                           | 270 ++++++++++++++++--
 tools/bpf/bpftool/link.c                      |   9 +
 tools/include/uapi/linux/bpf.h                |   5 +
 tools/lib/bpf/libbpf.c                        |   7 +
 tools/lib/bpf/libbpf.h                        |   2 +
 tools/lib/bpf/libbpf.map                      |   5 +
 tools/lib/bpf/libbpf_version.h                |   2 +-
 .../selftests/bpf/prog_tests/sockmap_basic.c  | 171 ++++++++++-
 .../selftests/bpf/prog_tests/sockmap_listen.c |  38 +++
 .../bpf/progs/test_skmsg_load_helpers.c       |  27 +-
 .../bpf/progs/test_sockmap_pass_prog.c        |  17 +-
 .../progs/test_sockmap_skb_verdict_attach.c   |   2 +-
 16 files changed, 537 insertions(+), 37 deletions(-)

-- 
2.43.0