[bpf-next,v2,0/6] Notify user space when a struct_ops object is detached/unregistered

Message

Kui-Feng Lee May 7, 2024, 5:55 a.m. UTC

The subsystems managing struct_ops objects may need to detach a
struct_ops object due to errors or other reasons. It would be useful
to notify user space programs so that error recovery or logging can be
carried out.

This patch set enables the detach feature for struct_ops links and
send an event to epoll when a link is detached.  Subsystems could call
link->ops->detach() to detach a link and notify user space programs
through epoll.

The signatures of callback functions in "struct bpf_struct_ops" have
been changed as well to pass an extra link argument to
subsystems. Subsystems could detach the links received from reg() and
update() callbacks if there is. This also provides a way that
subsystems can distinguish registrations for an object that has been
registered multiple times for several links.

However, bpf struct_ops maps without BPF_F_LINK have no any link.
Subsystems will receive NULL link pointer for this case.

---
Changes from v1:

 - Pass a link to reg, unreg, and update callbacks.

 - Provide a function to detach a link from underlying subsystems.

 - Add a kfunc to minic detachments from subsystems, and provide a
   flexible way to control when to do detachments.

 - Add two tests to detach a link from the subsystem after the refcount
   of the link drops to zero.

v1: https://lore.kernel.org/all/[e-mail]/

Kui-Feng Lee (6):
  bpf: pass bpf_struct_ops_link to callbacks in bpf_struct_ops.
  bpf: enable detaching links of struct_ops objects.
  bpf: support epoll from bpf struct_ops links.
  selftests/bpf: test struct_ops with epoll
  selftests/bpf: detach a struct_ops link from the subsystem managing
    it.
  selftests/bpf: make sure bpf_testmod handling racing link destroying
    well.

 include/linux/bpf.h                           |   7 +-
 kernel/bpf/bpf_struct_ops.c                   |  77 ++++++--
 kernel/bpf/syscall.c                          |  11 ++
 net/bpf/bpf_dummy_struct_ops.c                |   4 +-
 net/ipv4/bpf_tcp_ca.c                         |   6 +-
 .../bpf/bpf_test_no_cfi/bpf_test_no_cfi.c     |   4 +-
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  40 ++++-
 .../bpf/bpf_testmod/bpf_testmod_kfunc.h       |   1 +
 .../bpf/prog_tests/test_struct_ops_module.c   | 166 ++++++++++++++++++
 .../selftests/bpf/progs/struct_ops_detach.c   |  37 ++++
 10 files changed, 329 insertions(+), 24 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_detach.c