zdtm: add UDP multicast checkpoint/restore test

test/zdtm/static/Makefile

@@ -37,6 +37,7 @@ TST_NOFILE	:=				\
 		socket_udp-corked		\
 		socket6_udp			\
 		socket_udp_shutdown		\
+                socket_udp-multicast           \
 		socket_icmp			\
 		socket6_icmp			\
 		sk-freebind			\

test/zdtm/static/socket_udp-multicast.c

@@ -0,0 +1,115 @@
+#include "zdtmtst.h"
+
+const char *test_doc = "static test for UDP multicast socket membership\n";
+const char *test_author = "Piyush Khobragade\n";
+
+#include <stdio.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <sys/time.h>
+#include <errno.h>
+
+#define MCAST_GRP "239.0.0.1"
+#define PORT 8888
+#define MSG "mcast_test"
+#define LOCAL_IF "127.0.0.1"
+
+int main(int argc, char **argv)
+{
+        int sock;
+        int loop = 1;
+        struct sockaddr_in addr = {0};
+        struct sockaddr_in group = {0};
+        struct ip_mreq mreq;
+        char buf[32];
+        int ret;
+        struct in_addr local_addr;
+        struct timeval tv;
+
+        test_init(argc, argv);
+
+        local_addr.s_addr = inet_addr(LOCAL_IF);
+
+        sock = socket(AF_INET, SOCK_DGRAM, 0);
+        if (sock < 0) {
+                pr_perror("socket");
+                return 1;
+        }
+
+        // 1. Force loopback delivery
+        if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop)) < 0) {
+                pr_perror("IP_MULTICAST_LOOP");
+                return 1;
+        }
+
+        // 2. Set 2-second timeout on recv() so we don't hang if membership is lost
+        tv.tv_sec = 2;
+        tv.tv_usec = 0;
+        if (setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)) < 0) {
+                pr_perror("SO_RCVTIMEO");
+                return 1;
+        }
+
+        addr.sin_family = AF_INET;
+        addr.sin_port = htons(PORT);
+        addr.sin_addr.s_addr = htonl(INADDR_ANY);
+
+        if (bind(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
+                pr_perror("bind");
+                return 1;
+        }
+
+        // Join multicast strictly on the loopback interface
+        mreq.imr_multiaddr.s_addr = inet_addr(MCAST_GRP);
+        mreq.imr_interface = local_addr;
+        if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)) < 0) {
+                pr_perror("IP_ADD_MEMBERSHIP");
+                return 1;
+        }
+
+        test_daemon();
+        test_waitsig();
+
+        // FIX: Force egress traffic strictly through loopback to bypass isolated routing tables
+        if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF, &local_addr, sizeof(local_addr)) < 0) {
+                pr_perror("IP_MULTICAST_IF");
+                return 1;
+        }
+
+        group.sin_family = AF_INET;
+        group.sin_port = htons(PORT);
+        group.sin_addr.s_addr = inet_addr(MCAST_GRP);
+
+        ret = sendto(sock, MSG, strlen(MSG), 0, (struct sockaddr *)&group, sizeof(group));
+        if (ret != strlen(MSG)) {
+                fail("sendto failed");
+                return 1;
+        }
+
+        memset(buf, 0, sizeof(buf));
+        ret = recv(sock, buf, sizeof(buf), 0);
+
+        if (ret < 0) {
+                if (errno == EAGAIN || errno == EWOULDBLOCK) {
+                        fail("Multicast membership lost across restore (recv timed out)");
+                } else {
+                        pr_perror("recv failed");
+                }
+                return 1;
+        }
+
+        if (ret != strlen(MSG)) {
+                fail("recv length mismatch");
+                return 1;
+        }
+
+        if (memcmp(buf, MSG, strlen(MSG)) != 0) {
+                fail("message mismatch");
+                return 1;
+        }
+
+        pass();
+        return 0;
+}