[RFC,bpf-next,v2,0/9] Registrating struct_ops types from modules

Message

Kui-Feng Lee Sept. 13, 2023, 6:14 a.m. UTC

From: Kui-Feng Lee <[e-mail]>

Given the current constraints of the current implementation,
struct_ops cannot be registered dynamically. This presents a
significant limitation for modules like coming fuse-bpf, which seeks
to implement a new struct_ops type. To address this issue, a new API
is introduced that allows the registration of new struct_ops types
from modules.

Previously, struct_ops types were defined in bpf_struct_ops_types.h
and collected as a static array. The new API lets callers add new
struct_ops types to the array dynamically.

The struct_ops subsystem relies on BTF to determine the layout of
values in a struct_ops map and identify the subsystem that the
struct_ops map registers to. However, the kernel BTF does not include
the type information of struct_ops types defined by a module. The
struct_ops subsystem requires knowledge of the corresponding module
for a given struct_ops map and the utilization of BTF information from
that module. We empower libbpf to determine the correct module for
accessing the BTF information and pass an identity (FD) to the kernel.

If a module exits while one or more struct_ops maps still refer to a
struct_ops type defined by the module, it can lead to unforeseen
complications. Therefore, it is crucial to ensure that a module
remains intact as long as any struct_ops map is still linked to a
struct_ops type defined by the module. To achieve this, you can hold a
reference to the module for each struct_ops map.

Kui-Feng Lee (9):
  bpf: refactory struct_ops type initialization to a function.
  bpf: add register and unregister functions for struct_ops.
  bpf: attach a module BTF to a bpf_struct_ops
  bpf: use attached BTF to find correct type info of struct_ops progs.
  bpf: hold module for bpf_struct_ops_map.
  libbpf: Find correct module BTFs for struct_ops maps and progs.
  bpf: export btf_ctx_access to modules.
  selftests/bpf: test case for register_bpf_struct_ops().
  Comments and debug

 include/linux/bpf.h                           |  19 +-
 include/linux/btf.h                           |   1 +
 include/uapi/linux/bpf.h                      |   4 +
 kernel/bpf/bpf_struct_ops.c                   | 346 +++++++++++++-----
 kernel/bpf/btf.c                              |   3 +-
 kernel/bpf/syscall.c                          |   8 +-
 kernel/bpf/verifier.c                         |   4 +-
 tools/include/uapi/linux/bpf.h                |   4 +
 tools/lib/bpf/bpf.c                           |   3 +-
 tools/lib/bpf/bpf.h                           |   4 +-
 tools/lib/bpf/libbpf.c                        | 147 +++++---
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  84 +++++
 .../selftests/bpf/bpf_testmod/bpf_testmod.h   |   5 +
 .../bpf/prog_tests/test_struct_ops_module.c   |  40 ++
 .../selftests/bpf/progs/struct_ops_module.c   |  30 ++
 15 files changed, 558 insertions(+), 144 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_module.c