On Wed, Sep 29, 2021 at 11:30 PM Kumar Kartikeya Dwivedi
[off-list ref] wrote:

This commit moves BTF ID lookup into the newly added registration
helper, in a way that the bbr, cubic, and dctcp implementation set up
their sets in the bpf_tcp_ca kfunc_btf_set list, while the ones not
dependent on modules are looked up from the wrapper function.

This lifts the restriction for them to be compiled as built in objects,
and can be loaded as modules if required. Also modify Makefile.modfinal
to call resolve_btfids for each module.

Note that since kernel kfunc_ids never overlap with module kfunc_ids, we
only match the owner for module btf id sets.

See following commits for background on use of:

 CONFIG_X86 ifdef:
 569c484f9995 (bpf: Limit static tcp-cc functions in the .BTF_ids list to x86)

 CONFIG_DYNAMIC_FTRACE ifdef:
 7aae231ac93b (bpf: tcp: Limit calling some tcp cc functions to CONFIG_DYNAMIC_FTRACE)

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/btf.h       |  4 ++++
 kernel/bpf/btf.c          |  3 +++
 net/ipv4/bpf_tcp_ca.c     | 34 +++-------------------------------
 net/ipv4/tcp_bbr.c        | 28 +++++++++++++++++++++++++++-
 net/ipv4/tcp_cubic.c      | 26 +++++++++++++++++++++++++-
 net/ipv4/tcp_dctcp.c      | 26 +++++++++++++++++++++++++-
 scripts/Makefile.modfinal |  1 +
 7 files changed, 88 insertions(+), 34 deletions(-)

[...]

 BTF_SET_END(bpf_tcp_ca_kfunc_ids)

 static bool bpf_tcp_ca_check_kfunc_call(u32 kfunc_btf_id, struct module *owner)
 {
-       return btf_id_set_contains(&bpf_tcp_ca_kfunc_ids, kfunc_btf_id);
+       if (btf_id_set_contains(&bpf_tcp_ca_kfunc_ids, kfunc_btf_id))
+               return true;
+       return __bpf_tcp_ca_check_kfunc_call(kfunc_btf_id, owner);

so here, why it can't be generic

__bpf_check_kfunc_call(&bpf_tcp_ca_kfunc_list, kfunc_btf_id, owner);

?

 }

 static const struct bpf_verifier_ops bpf_tcp_ca_verifier_ops = {

[...]