[PATCH bpf-next v1 0/3] Allow struct_ops to get bpf_map during

[Amery Hung <ameryhung@xxxxxxxxx>]

This patchset allows struct_ops implementors to access bpf_map during
reg() and unreg() so that they can create an id to struct_ops instance
mapping. This in turn allows struct_ops kfuncs to refer to the instance
without passing a pointer to the struct_ops. The selftest provides an
end-to-end example.

Some struct_ops users extend themselves with other bpf programs, which
also need to call struct_ops kfuncs. For example, scx_layered uses
syscall bpf programs as a scx_layered specific control plane and uses
tracing programs to get additional information for scheduling [0].
The kfuncs may need to refer to the struct_ops instance and perform
jobs accordingly. To allow calling struct_ops kfuncs referring to
specific instances from different program types and context (e.g.,
struct_ops, tracing, async callbacks), the traditional way is to pass
the struct_ops pointer to kfuncs.

This patchset provides an alternative way, through a combination of
bpf map id and global variable. First, a struct_ops implementor will
use the map id of the struct_ops map as the id of an instance. Then, 
it needs to maintain an id to instance mapping: inserting a new mapping
during reg() and removing it during unreg(). The map id can be acquired
by calling bpf_struct_ops_get(), which is tweaked to return bpf_map
instead of bool.

[0] https://github.com/sched-ext/scx/blob/main/scheds/rust/scx_layered/src/bpf/main.bpf.c


Amery Hung (3):
  bpf: Allow getting bpf_map from struct_ops kdata
  selftests/bpf: Add multi_st_ops that supports multiple instances
  selftests/bpf: Test multi_st_ops and calling kfuncs from different
    programs

 include/linux/bpf.h                           |   4 +-
 kernel/bpf/bpf_struct_ops.c                   |   7 +-
 .../test_struct_ops_id_ops_mapping.c          |  77 ++++++++++++
 .../bpf/progs/struct_ops_id_ops_mapping1.c    |  57 +++++++++
 .../bpf/progs/struct_ops_id_ops_mapping2.c    |  57 +++++++++
 .../selftests/bpf/test_kmods/bpf_testmod.c    | 112 ++++++++++++++++++
 .../selftests/bpf/test_kmods/bpf_testmod.h    |   8 ++
 .../bpf/test_kmods/bpf_testmod_kfunc.h        |   2 +
 8 files changed, 319 insertions(+), 5 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_id_ops_mapping.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_id_ops_mapping1.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_id_ops_mapping2.c

-- 
2.47.3