selftests/bpf: Remove "&>" usage in the selftests

In s390, CI reported that the sock_iter_batch selftest
hits this error very often:

2024-01-26T16:56:49.3091804Z Bind /proc/self/ns/net -> /run/netns/sock_iter_batch_netns failed: No such file or directory
2024-01-26T16:56:49.3149524Z Cannot remove namespace file "/run/netns/sock_iter_batch_netns": No such file or directory
2024-01-26T16:56:49.3772213Z test_sock_iter_batch:FAIL:ip netns add sock_iter_batch_netns unexpected error: 256 (errno 0)

It happens very often in s390 but Manu also noticed it happens very
sparsely in other arch also.

It turns out the default dash shell does not recognize "&>"
as a redirection operator, so the command went to the background.
In the sock_iter_batch selftest, the "ip netns delete" went
into background and then race with the following "ip netns add"
command.

This patch replaces the "&> /dev/null" usage with ">/dev/null 2>&1"
and does this redirection in the SYS_NOFAIL macro instead of doing
it individually by its caller. The SYS_NOFAIL callers do not care
about failure, so it is no harm to do this redirection even if
some of the existing callers do not redirect to /dev/null now.

It touches different test files, so I skipped the Fixes tags
in this patch. Some of the changed tests do not use "&>"
but they use the SYS_NOFAIL, so these tests are also
changed to avoid doing its own redirection because
SYS_NOFAIL does it internally now.

Signed-off-by: Martin KaFai Lau <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 		bpf_tc_hook_destroy(&qdisc_hook);
 		close_netns(nstoken);
 	}
-	SYS_NOFAIL("ip netns del " NS_TEST " &> /dev/null");
+	SYS_NOFAIL("ip netns del " NS_TEST);
 	decap_sanity__destroy(skel);
 }

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

···
 fail:
 	if (nstoken)
 		close_netns(nstoken);
-	SYS_NOFAIL("ip netns del " NS_TEST " &> /dev/null");
+	SYS_NOFAIL("ip netns del " NS_TEST);
 	fib_lookup__destroy(skel);
 }

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

···
 	/* Wait for up to 5s for links to come up */
 	for (i = 0; i < 5; ++i) {
 		if (ipv6)
-			up = !system("ip netns exec " NS0 " ping -6 -c 1 -W 1 " VETH1_ADDR6 " &>/dev/null");
+			up = !SYS_NOFAIL("ip netns exec " NS0 " ping -6 -c 1 -W 1 " VETH1_ADDR6);
 		else
-			up = !system("ip netns exec " NS0 " ping -c 1 -W 1 " VETH1_ADDR " &>/dev/null");
+			up = !SYS_NOFAIL("ip netns exec " NS0 " ping -c 1 -W 1 " VETH1_ADDR);
 
 		if (up)
 			break;

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

···
 		snprintf(ip, sizeof(ip), "20.0.0.%d", link_index);
 
 	/* We won't get a reply. Don't fail here */
-	SYS_NOFAIL("ping %s -c1 -W1 -s %d >/dev/null 2>&1",
+	SYS_NOFAIL("ping %s -c1 -W1 -s %d",
 		   ip, ICMP_PAYLOAD_SIZE);
 }
 

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

···
 static void ping_once(const char *ip)
 {
 	/* We won't get a reply. Don't fail here */
-	SYS_NOFAIL("ping %s -c1 -W1 -s %d >/dev/null 2>&1",
+	SYS_NOFAIL("ping %s -c1 -W1 -s %d",
 		   ip, ICMP_PAYLOAD_SIZE);
 }
 

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

···
 	if (nstoken)
 		close_netns(nstoken);
 
-	SYS_NOFAIL("ip netns del %s &> /dev/null", NS_TEST);
+	SYS_NOFAIL("ip netns del %s", NS_TEST);
 }
 
 static int verify_tsk(int map_fd, int client_fd)

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

···
 cleanup:
 	if (nstoken)
 		close_netns(nstoken);
-	SYS_NOFAIL("ip netns del " TEST_NS " &> /dev/null");
+	SYS_NOFAIL("ip netns del " TEST_NS);
 	if (cgroup_fd >= 0)
 		close(cgroup_fd);
 	sock_destroy_prog__destroy(skel);

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

···
 {
 	struct nstoken *nstoken = NULL;
 
-	SYS_NOFAIL("ip netns del " TEST_NS " &> /dev/null");
+	SYS_NOFAIL("ip netns del " TEST_NS);
 	SYS(done, "ip netns add %s", TEST_NS);
 	SYS(done, "ip -net %s link set dev lo up", TEST_NS);
 
···
 	close_netns(nstoken);
 
 done:
-	SYS_NOFAIL("ip netns del " TEST_NS " &> /dev/null");
+	SYS_NOFAIL("ip netns del " TEST_NS);
 }

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

···
 static void cleanup(void)
 {
 	SYS_NOFAIL("test -f /var/run/netns/at_ns0 && ip netns delete at_ns0");
-	SYS_NOFAIL("ip link del veth1 2> /dev/null");
-	SYS_NOFAIL("ip link del %s 2> /dev/null", VXLAN_TUNL_DEV1);
-	SYS_NOFAIL("ip link del %s 2> /dev/null", IP6VXLAN_TUNL_DEV1);
+	SYS_NOFAIL("ip link del veth1");
+	SYS_NOFAIL("ip link del %s", VXLAN_TUNL_DEV1);
+	SYS_NOFAIL("ip link del %s", IP6VXLAN_TUNL_DEV1);
 }
 
 static int add_vxlan_tunnel(void)
···
 static void delete_ipip_tunnel(void)
 {
 	SYS_NOFAIL("ip -n at_ns0 link delete dev %s", IPIP_TUNL_DEV0);
-	SYS_NOFAIL("ip -n at_ns0 fou del port 5555 2> /dev/null");
+	SYS_NOFAIL("ip -n at_ns0 fou del port 5555");
 	SYS_NOFAIL("ip link delete dev %s", IPIP_TUNL_DEV1);
-	SYS_NOFAIL("ip fou del port 5555 2> /dev/null");
+	SYS_NOFAIL("ip fou del port 5555");
 }
 
 static int add_xfrm_tunnel(void)
···
 
 static void delete_xfrm_tunnel(void)
 {
-	SYS_NOFAIL("ip xfrm policy delete dir out src %s/32 dst %s/32 2> /dev/null",
+	SYS_NOFAIL("ip xfrm policy delete dir out src %s/32 dst %s/32",
 		   IP4_ADDR_TUNL_DEV1, IP4_ADDR_TUNL_DEV0);
-	SYS_NOFAIL("ip xfrm policy delete dir in src %s/32 dst %s/32 2> /dev/null",
+	SYS_NOFAIL("ip xfrm policy delete dir in src %s/32 dst %s/32",
 		   IP4_ADDR_TUNL_DEV0, IP4_ADDR_TUNL_DEV1);
-	SYS_NOFAIL("ip xfrm state delete src %s dst %s proto esp spi %d 2> /dev/null",
+	SYS_NOFAIL("ip xfrm state delete src %s dst %s proto esp spi %d",
 		   IP4_ADDR_VETH0, IP4_ADDR1_VETH1, XFRM_SPI_IN_TO_OUT);
-	SYS_NOFAIL("ip xfrm state delete src %s dst %s proto esp spi %d 2> /dev/null",
+	SYS_NOFAIL("ip xfrm state delete src %s dst %s proto esp spi %d",
 		   IP4_ADDR1_VETH1, IP4_ADDR_VETH0, XFRM_SPI_OUT_TO_IN);
 }
 

tools/testing/selftests/bpf/test_progs.h

···
 			goto goto_label;				\
 	})
 
+#define ALL_TO_DEV_NULL " >/dev/null 2>&1"
+
 #define SYS_NOFAIL(fmt, ...)						\
 	({								\
 		char cmd[1024];						\
-		snprintf(cmd, sizeof(cmd), fmt, ##__VA_ARGS__);		\
+		int n;							\
+		n = snprintf(cmd, sizeof(cmd), fmt, ##__VA_ARGS__);	\
+		if (n < sizeof(cmd) && sizeof(cmd) - n >= sizeof(ALL_TO_DEV_NULL)) \
+			strcat(cmd, ALL_TO_DEV_NULL);			\
 		system(cmd);						\
 	})