bpf, test_run: Propagate bpf_flow_dissect's retval to user's bpf_attr.test.retval

Formerly, a boolean denoting whether bpf_flow_dissect returned BPF_OK
was set into 'bpf_attr.test.retval'.

Augment this, so users can check the actual return code of the dissector
program under test.

Existing prog_tests/flow_dissector*.c tests were correspondingly changed
to check against each test's expected retval.

Also, tests' resulting 'flow_keys' are verified only in case the expected
retval is BPF_OK. This allows adding new tests that expect non BPF_OK.

Signed-off-by: Shmulik Ladkani <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Reviewed-by: Stanislav Fomichev <[e-mail]>
Acked-by: John Fastabend <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

net/bpf/test_run.c

···
 	bpf_test_timer_enter(&t);
 	do {
 		retval = bpf_flow_dissect(prog, &ctx, eth->h_proto, ETH_HLEN,
-					  size, flags) == BPF_OK;
+					  size, flags);
 	} while (bpf_test_timer_continue(&t, 1, repeat, &ret, &duration));
 	bpf_test_timer_leave(&t);
 

tools/testing/selftests/bpf/prog_tests/flow_dissector.c

···
 	} pkt;
 	struct bpf_flow_keys keys;
 	__u32 flags;
+	__u32 retval;
 };
 
 #define VLAN_HLEN	4
···
 			.sport = 80,
 			.dport = 8080,
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipv6",
···
 			.sport = 80,
 			.dport = 8080,
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "802.1q-ipv4",
···
 			.sport = 80,
 			.dport = 8080,
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "802.1ad-ipv6",
···
 			.sport = 80,
 			.dport = 8080,
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipv4-frag",
···
 			.dport = 8080,
 		},
 		.flags = BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG,
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipv4-no-frag",
···
 			.is_frag = true,
 			.is_first_frag = true,
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipv6-frag",
···
 			.dport = 8080,
 		},
 		.flags = BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG,
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipv6-no-frag",
···
 			.is_frag = true,
 			.is_first_frag = true,
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipv6-flow-label",
···
 			.dport = 8080,
 			.flow_label = __bpf_constant_htonl(0xbeeef),
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipv6-no-flow-label",
···
 			.flow_label = __bpf_constant_htonl(0xbeeef),
 		},
 		.flags = BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL,
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipip-encap",
···
 			.sport = 80,
 			.dport = 8080,
 		},
+		.retval = BPF_OK,
 	},
 	{
 		.name = "ipip-no-encap",
···
 			.is_encap = true,
 		},
 		.flags = BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP,
+		.retval = BPF_OK,
 	},
 };
 
···
 		err = tx_tap(tap_fd, &tests[i].pkt, sizeof(tests[i].pkt));
 		CHECK(err < 0, "tx_tap", "err %d errno %d\n", err, errno);
 
+		/* check the stored flow_keys only if BPF_OK expected */
+		if (tests[i].retval != BPF_OK)
+			continue;
+
 		err = bpf_map_lookup_elem(keys_fd, &key, &flow_keys);
 		ASSERT_OK(err, "bpf_map_lookup_elem");
 
···
 
 		err = bpf_prog_test_run_opts(prog_fd, &topts);
 		ASSERT_OK(err, "test_run");
-		ASSERT_EQ(topts.retval, 1, "test_run retval");
+		ASSERT_EQ(topts.retval, tests[i].retval, "test_run retval");
+
+		/* check the resulting flow_keys only if BPF_OK returned */
+		if (topts.retval != BPF_OK)
+			continue;
 		ASSERT_EQ(topts.data_size_out, sizeof(flow_keys),
 			  "test_run data_size_out");
 		CHECK_FLOW_KEYS(tests[i].name, flow_keys, tests[i].keys);

tools/testing/selftests/bpf/prog_tests/flow_dissector_load_bytes.c

···
 	ASSERT_OK(err, "test_run");
 	ASSERT_EQ(topts.data_size_out, sizeof(flow_keys),
 		  "test_run data_size_out");
-	ASSERT_EQ(topts.retval, 1, "test_run retval");
+	ASSERT_EQ(topts.retval, BPF_OK, "test_run retval");
 
 	if (fd >= -1)
 		close(fd);