Re: [PATCH bpf 2/2] bpf: selftests: Add non function pointer test to struct_ops

On Wed, Feb 10, 2021 at 12:27:38PM -0800, Andrii Nakryiko wrote:

On Tue, Feb 9, 2021 at 12:11 PM Martin KaFai Lau [off-list ref] wrote:

quoted

This patch adds a "void *owner" member.  The existing
bpf_tcp_ca test will ensure the bpf_cubic.o and bpf_dctcp.o
can be loaded.

Signed-off-by: Martin KaFai Lau <redacted>
---

Acked-by: Andrii Nakryiko <andrii@kernel.org>

What will happen if BPF code initializes such non-func ptr member?
Will libbpf complain or just ignore those values? Ignoring initialized
members isn't great.

The latter. libbpf will ignore non-func ptr member.  The non-func ptr
member stays zero when it is passed to the kernel.

libbpf can be changed to copy this non-func ptr value.
The kernel will decide what to do with it.  It will
then be consistent with int/array member like ".name"
and ".flags" where the kernel will verify the value.
I can spin v2 to do that.

quoted

 tools/testing/selftests/bpf/bpf_tcp_helpers.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/bpf/bpf_tcp_helpers.h b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
index 6a9053162cf2..91f0fac632f4 100644
--- a/tools/testing/selftests/bpf/bpf_tcp_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_tcp_helpers.h

@@ -177,6 +177,7 @@ struct tcp_congestion_ops {
         * after all the ca_state processing. (optional)
         */
        void (*cong_control)(struct sock *sk, const struct rate_sample *rs);
+       void *owner;
 };

 #define min(a, b) ((a) < (b) ? (a) : (b))
--

2.24.1