This example shows how it is possible to:
Identify the parent msk of an MPTCP subflow.
Put different sockopt for each subflow of a same MPTCP connection.
Here especially, two different behaviours are implemented:
A socket mark (SOL_SOCKET SO_MARK) is put on each subflow of a same
MPTCP connection. The order of creation of the current subflow defines
its mark. The TCP CC algorithm of the very first subflow of an MPTCP
connection is set to "reno".
This is just to show it is possible to identify an MPTCP connection, and
set socket options, from different SOL levels, per subflow. "reno" has
been picked because it is built-in and usually not set as default one.
It is easy to verify with 'ss' that these modifications have been
applied correctly. That's what the next patch is going to do.
Nicolas' code comes from:
commit 4d120186e4d6 ("bpf:examples: update mptcp_set_mark_kern.c")
from the MPTCP repo https://github.com/multipath-tcp/mptcp_net-next (the
"scripts" branch), and it has been adapted by Geliang.
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/76
Co-developed-by: Geliang Tang <tanggeliang@xxxxxxxxxx>
Signed-off-by: Geliang Tang <tanggeliang@xxxxxxxxxx>
Signed-off-by: Nicolas Rybowski <nicolas.rybowski@xxxxxxxxxxxx>
Reviewed-by: Mat Martineau <martineau@xxxxxxxxxx>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
---
Notes:
- v1 -> v2:
- The commit message has been updated: why setting multiple socket
options, why reno, the verification is done in a later patch
(different author). (Alexei)
- v2 -> v3:
- Only #include "bpf_tracing_net.h", linked to:
https://lore.kernel.org/20240509175026.3423614-1-martin.lau@xxxxxxxxx
---
tools/testing/selftests/bpf/progs/mptcp_subflow.c | 59 +++++++++++++++++++++++
1 file changed, 59 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/mptcp_subflow.c b/tools/testing/selftests/bpf/progs/mptcp_subflow.c
new file mode 100644
index 000000000000..bc572e1d6df8
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mptcp_subflow.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020, Tessares SA. */
+/* Copyright (c) 2024, Kylin Software */
+
+/* vmlinux.h, bpf_helpers.h and other 'define' */
+#include "bpf_tracing_net.h"
+
+char _license[] SEC("license") = "GPL";
+
+char cc[TCP_CA_NAME_MAX] = "reno";
+
+/* Associate a subflow counter to each token */
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(__u32));
+ __uint(max_entries, 100);
+} mptcp_sf SEC(".maps");
+
+SEC("sockops")
+int mptcp_subflow(struct bpf_sock_ops *skops)
+{
+ __u32 init = 1, key, mark, *cnt;
+ struct mptcp_sock *msk;
+ struct bpf_sock *sk;
+ int err;
+
+ if (skops->op != BPF_SOCK_OPS_TCP_CONNECT_CB)
+ return 1;
+
+ sk = skops->sk;
+ if (!sk)
+ return 1;
+
+ msk = bpf_skc_to_mptcp_sock(sk);
+ if (!msk)
+ return 1;
+
+ key = msk->token;
+ cnt = bpf_map_lookup_elem(&mptcp_sf, &key);
+ if (cnt) {
+ /* A new subflow is added to an existing MPTCP connection */
+ __sync_fetch_and_add(cnt, 1);
+ mark = *cnt;
+ } else {
+ /* A new MPTCP connection is just initiated and this is its primary subflow */
+ bpf_map_update_elem(&mptcp_sf, &key, &init, BPF_ANY);
+ mark = init;
+ }
+
+ /* Set the mark of the subflow's socket based on appearance order */
+ err = bpf_setsockopt(skops, SOL_SOCKET, SO_MARK, &mark, sizeof(mark));
+ if (err < 0)
+ return 1;
+ if (mark == 1)
+ err = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION, cc, TCP_CA_NAME_MAX);
+
+ return 1;
+}
--
2.45.2
