The last few month BPF community has been discussing an approach to call
chaining, since exiting bpt_tail_call() mechanism used in production XDP
programs has plenty of downsides. The outcome of these discussion was a
conclusion to implement dynamic re-linking of BPF programs. Where rootlet XDP
program attached to a netdevice can programmatically define a policy of
execution of other XDP programs. Such rootlet would be compiled as normal XDP
program and provide a number of placeholder global functions which later can be
replaced with future XDP programs. BPF trampoline, function by function
verification were building blocks towards that goal. The patch 1 is a final
building block. It introduces dynamic program extensions. A number of
improvements like more flexible function by function verification and better
libbpf api will be implemented in future patches.

v1->v2:
- addressed Andrii's comments
- rebase

Alexei Starovoitov (3):
  bpf: Introduce dynamic program extensions
  libbpf: Add support for program extensions
  selftests/bpf: Add tests for program extensions

 include/linux/bpf.h                           |  10 +-
 include/linux/bpf_types.h                     |   2 +
 include/linux/btf.h                           |   5 +
 include/uapi/linux/bpf.h                      |   1 +
 kernel/bpf/btf.c                              | 152 +++++++++++++++++-
 kernel/bpf/syscall.c                          |  15 +-
 kernel/bpf/trampoline.c                       |  41 ++++-
 kernel/bpf/verifier.c                         |  85 +++++++---
 tools/include/uapi/linux/bpf.h                |   1 +
 tools/lib/bpf/bpf.c                           |   3 +-
 tools/lib/bpf/libbpf.c                        |  13 +-
 tools/lib/bpf/libbpf.h                        |   2 +
 tools/lib/bpf/libbpf.map                      |   2 +
 tools/lib/bpf/libbpf_probes.c                 |   1 +
 .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  |  20 ++-
 .../selftests/bpf/progs/fexit_bpf2bpf.c       |  57 +++++++
 .../selftests/bpf/progs/test_pkt_access.c     |   8 +-
 17 files changed, 384 insertions(+), 34 deletions(-)

-- 
2.23.0