selftests/bpf: Handle !CONFIG_SMC in bpf_smc.c

Currently BPF selftests will fail to compile if CONFIG_SMC
is not set.

Use BPF CO-RE to work around the case where CONFIG_SMC is
not set; use ___local variants of relevant structures and
utilize bpf_core_field_exists() for net->smc.

The test continues to pass where

  CONFIG_SMC=y
  CONFIG_SMC_HS_CTRL_BPF=y

but these changes allow the selftests to build in the absence
of CONFIG_SMC=y.

Also ensure that we get a pure skip rather than a skip+fail
by removing the SMC is unsupported part from the ASSERT_FALSE()
in get_smc_nl_family(); doing this means we get a skip without
a fail when CONFIG_SMC is not set:

$ sudo ./test_progs -t bpf_smc
Summary: 1/0 PASSED, 1 SKIPPED, 0 FAILED

Fixes: beb3c67297d9 ("bpf/selftests: Add selftest for bpf_smc_hs_ctrl")
Reported-by: Colm Harrington <colm.harrington@oracle.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Tested-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://patch.msgid.link/20260310111330.601765-1-alan.maguire@oracle.com

2 files changed, 30 insertions, 4 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/test_bpf_smc.c b/tools/testing/selftests/bpf/prog_tests/test_bpf_smc.c
index de22734abc4d..40d38280c091 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_bpf_smc.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_bpf_smc.c
@@ -131,8 +131,10 @@ static bool get_smc_nl_family_id(void)
 		goto fail;
 
 	ret = recv(fd, &msg, sizeof(msg), 0);
-	if (!ASSERT_FALSE(msg.n.nlmsg_type == NLMSG_ERROR || ret < 0 ||
-			  !NLMSG_OK(&msg.n, ret), "nl_family response"))
+	if (msg.n.nlmsg_type == NLMSG_ERROR)
+		goto fail;
+	if (!ASSERT_FALSE(ret < 0 || !NLMSG_OK(&msg.n, ret),
+			  "nl_family response"))
 		goto fail;
 
 	nl = (struct nlattr *)GENLMSG_DATA(&msg);
diff --git a/tools/testing/selftests/bpf/progs/bpf_smc.c b/tools/testing/selftests/bpf/progs/bpf_smc.c
index 70d8b08f5914..6263a45bf006 100644
--- a/tools/testing/selftests/bpf/progs/bpf_smc.c
+++ b/tools/testing/selftests/bpf/progs/bpf_smc.c
@@ -8,6 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
+#ifndef SMC_HS_CTRL_NAME_MAX
+#define SMC_HS_CTRL_NAME_MAX 16
+#endif
+
 enum {
 	BPF_SMC_LISTEN	= 10,
 };
@@ -18,6 +22,20 @@ struct smc_sock___local {
 	bool use_fallback;
 } __attribute__((preserve_access_index));
 
+struct smc_hs_ctrl___local {
+	char name[SMC_HS_CTRL_NAME_MAX];
+	int (*syn_option)(struct tcp_sock *);
+	int (*synack_option)(const struct tcp_sock  *, struct inet_request_sock *);
+} __attribute__((preserve_access_index));
+
+struct netns_smc___local {
+	struct smc_hs_ctrl___local *hs_ctrl;
+} __attribute__((preserve_access_index));
+
+struct net___local {
+	struct netns_smc___local smc;
+} __attribute__((preserve_access_index));
+
 int smc_cnt = 0;
 int fallback_cnt = 0;
 
@@ -88,8 +106,14 @@ int BPF_PROG(smc_run, int family, int type, int protocol)
 
 	task = bpf_get_current_task_btf();
 	/* Prevent from affecting other tests */
-	if (!task || !task->nsproxy->net_ns->smc.hs_ctrl)
+	if (!task) {
 		return protocol;
+	} else {
+		struct net___local *net = (struct net___local *)task->nsproxy->net_ns;
+
+		if (!bpf_core_field_exists(struct net___local, smc) || !net->smc.hs_ctrl)
+			return protocol;
+	}
 
 	return IPPROTO_SMC;
 }
@@ -110,7 +134,7 @@ int BPF_PROG(bpf_smc_set_tcp_option, struct tcp_sock *tp)
 }
 
 SEC(".struct_ops")
-struct smc_hs_ctrl  linkcheck = {
+struct smc_hs_ctrl___local  linkcheck = {
 	.name		= "linkcheck",
 	.syn_option	= (void *)bpf_smc_set_tcp_option,
 	.synack_option	= (void *)bpf_smc_set_tcp_option_cond,