[PATCH net v2 2/2] selftests/bpf: check epoll readiness after reuseport migration

[Zhenzhong Wu <jt26wzz@gmail.com>]

After migrate_dance() moves established children to the target
listener, add it to an epoll set and verify that epoll_wait(..., 0)
reports it ready before accept().

This adds epoll coverage for the TCP_ESTABLISHED reuseport migration
case in migrate_reuseport.

Keep the check limited to TCP_ESTABLISHED cases. TCP_SYN_RECV and
TCP_NEW_SYN_RECV still depend on asynchronous handshake completion,
so a zero-timeout epoll_wait() would race there.

Signed-off-by: Zhenzhong Wu <jt26wzz@gmail.com>
---
 .../bpf/prog_tests/migrate_reuseport.c        | 32 ++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c b/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c
index 653b0a20f..580a53424 100644
--- a/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c
+++ b/tools/testing/selftests/bpf/prog_tests/migrate_reuseport.c
@@ -18,13 +18,16 @@
  *   9. call shutdown() for the second server
  *        and migrate the requests in the accept queue
  *        to the last server socket.
- *  10. call accept() for the last server socket.
+ *  10. for TCP_ESTABLISHED cases, call epoll_wait(..., 0)
+ *        for the last server socket.
+ *  11. call accept() for the last server socket.
  *
  * Author: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
  */
 
 #include <bpf/bpf.h>
 #include <bpf/libbpf.h>
+#include <sys/epoll.h>
 
 #include "test_progs.h"
 #include "test_migrate_reuseport.skel.h"
@@ -522,6 +525,33 @@ static void run_test(struct migrate_reuseport_test_case *test_case,
 			goto close_clients;
 	}
 
+	/* Only TCP_ESTABLISHED has already-migrated accept-queue entries
+	 * here.  Later states still depend on follow-up handshake work.
+	 */
+	if (test_case->state == BPF_TCP_ESTABLISHED) {
+		struct epoll_event ev = {
+			.events = EPOLLIN,
+		};
+		int epfd;
+		int nfds;
+
+		epfd = epoll_create1(EPOLL_CLOEXEC);
+		if (!ASSERT_NEQ(epfd, -1, "epoll_create1"))
+			goto close_clients;
+
+		ev.data.fd = test_case->servers[MIGRATED_TO];
+		if (!ASSERT_OK(epoll_ctl(epfd, EPOLL_CTL_ADD,
+					 test_case->servers[MIGRATED_TO], &ev),
+			       "epoll_ctl"))
+			goto close_epfd;
+
+		nfds = epoll_wait(epfd, &ev, 1, 0);
+		ASSERT_EQ(nfds, 1, "epoll_wait");
+
+close_epfd:
+		close(epfd);
+	}
+
 	count_requests(test_case, skel);
 
 close_clients:
-- 
2.43.0