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2024-09-30selftests/bpf: Add getsockopt to inspect mptcp subflowGeliang Tang
This patch adds a "cgroup/getsockopt" way to inspect the subflows of an MPTCP socket, and verify the modifications done by the same BPF program in the previous commit: a different mark per subflow, and a different TCP CC set on the second one. This new hook will be used by the next commit to verify the socket options set on each subflow. This extra "cgroup/getsockopt" prog walks the msk->conn_list and use bpf_core_cast to cast a pointer for readonly. It allows to inspect all the fields of a structure. Note that on the kernel side, the MPTCP socket stores a list of subflows under 'msk->conn_list'. They can be iterated using the generic 'list' helpers. They have been imported here, with a small difference: list_for_each_entry() uses 'can_loop' to limit the number of iterations, and ease its use. Because only data need to be read here, it is enough to use this technique. It is planned to use bpf_iter, when BPF programs will be used to modify data from the different subflows. mptcp_subflow_tcp_sock() and mptcp_for_each_stubflow() helpers have also be imported. Suggested-by: Martin KaFai Lau <martin.lau@kernel.org> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn> Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Link: https://lore.kernel.org/r/20240926-upstream-bpf-next-20240506-mptcp-subflow-test-v7-2-d26029e15cdd@kernel.org Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>