[PATCH v2] selftest: memcg: Skp memcg_sock test if address family not supported

[Waiman Long <longman@redhat.com>]

The test_memcg_sock test in memcontrol.c sets up an IPv6 socket and
send data over it to consume memory and verify that memory.stat.sock
and memory.current values are close.

On systems where IPv6 isn't enabled or not configured to support
SOCK_STREAM, the test_memcg_sock test always fails.  When the socket()
call fails, there is no way we can test the memory consumption and
verify the above claim. I believe it is better to just skip the test
in this case instead of reporting a test failure hinting that there
may be something wrong with the memcg code.

Fixes: 5f8f019380b8 ("selftests: cgroup/memcontrol: add basic test for socket accounting")
Signed-off-by: Waiman Long <longman@redhat.com>

[v2] Update and commit log & adjust the skip code as suggested by Michael.

---
 tools/testing/selftests/cgroup/test_memcontrol.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index 2fb096a2a9f9..a25eb097b31c 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -1280,8 +1280,11 @@ static int tcp_server(const char *cgroup, void *arg)
 	saddr.sin6_port = htons(srv_args->port);
 
 	sk = socket(AF_INET6, SOCK_STREAM, 0);
-	if (sk < 0)
+	if (sk < 0) {
+		/* Pass back errno to the ctl_fd */
+		write(ctl_fd, &errno, sizeof(errno));
 		return ret;
+	}
 
 	if (setsockopt(sk, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)) < 0)
 		goto cleanup;
@@ -1412,6 +1415,12 @@ static int test_memcg_sock(const char *root)
 			goto cleanup;
 		close(args.ctl[0]);
 
+		/* Skip if address family not supported by protocol */
+		if (err == EAFNOSUPPORT) {
+			ret = KSFT_SKIP;
+			goto cleanup;
+		}
+
 		if (!err)
 			break;
 		if (err != EADDRINUSE)
-- 
2.53.0