[PATCH iproute2-next 3/3] ip: netns: add "ip netns cookie" command

@@ -36,6 +36,7 @@ static int usage(void)
 		"	ip [-all] netns delete [NAME]\n"
 		"	ip netns identify [PID]\n"
 		"	ip netns pids NAME\n"
+		"	ip netns cookie [NAME | PID]\n"
 		"	ip [-all] netns exec [NAME] cmd ...\n"
 		"	ip netns monitor\n"
 		"	ip netns list-id [target-nsid POSITIVE-INT] [nsid POSITIVE-INT]\n"

@@ -710,6 +711,48 @@ static int netns_identify(int argc, char **argv)
 	return rc;
 }
 
+static int netns_cookie(int argc, char **argv)
+{
+	const char *str;
+	__u64 cookie;
+	int fd;
+
+	if (argc > 1) {
+		fprintf(stderr, "extra arguments specified\n");
+		return -1;
+	}
+
+	if (argc == 1) {
+		str = argv[0];
+		fd = netns_get_fd(str);
+	} else {
+		str = "/proc/self/ns/net";
+		fd = open(str, O_RDONLY);
+	}
+	if (fd < 0) {
+		fprintf(stderr, "Cannot open network namespace \"%s\": %s\n",
+			str, strerror(errno));
+		return -1;
+	}
+
+	if (ioctl(fd, NS_GET_ID, &cookie) < 0) {
+		fprintf(stderr,
+			"Cannot get cookie of network namespace \"%s\": %s\n",
+			str, strerror(errno));
+		close(fd);
+		return -1;
+	}
+	close(fd);
+
+	new_json_obj(json);
+	open_json_object(NULL);
+	print_u64(PRINT_ANY, "cookie", "%llu\n", cookie);
+	close_json_object();
+	delete_json_obj();
+
+	return 0;
+}
+
 static int on_netns_del(char *nsname, void *arg)
 {
 	char netns_path[PATH_MAX];

@@ -1055,6 +1098,9 @@ int do_netns(int argc, char **argv)
 	if (matches(*argv, "pids") == 0)
 		return netns_pids(argc-1, argv+1);
 
+	if (strcmp(*argv, "cookie") == 0)
+		return netns_cookie(argc-1, argv+1);
+
 	if (matches(*argv, "exec") == 0)
 		return netns_exec(argc-1, argv+1);
 

@@ -42,6 +42,10 @@ ip-netns \- process network namespace management
 .BR "ip netns pids"
 .I NETNSNAME
 
+.ti -8
+.BR "ip netns cookie"
+.RI "[ " NETNSNAME " | " PID " ]"
+
 .ti -8
 .BR "ip [-all] netns exec "
 .RI "[ " NETNSNAME " ] " command ...

@@ -182,6 +186,18 @@ not specified then the current process will be used.
 This command walks through proc and finds all of the process who have
 the named network namespace as their primary network namespace.
 
+.TP
+.B ip netns cookie [ NETNSNAME | PID ] - Report the cookie of a network namespace
+.sp
+This command displays the cookie of the named network namespace or of
+the network namespace of the process PID. If neither is specified, the
+cookie of the current network namespace is displayed. See
+.B ip netns list
+for a description of the cookie. Unlike
+.BR "ip netns list" ,
+this command can also be used with network namespaces that are not
+named, such as those created by container runtimes.
+
 .TP
 .B ip [-all] netns exec [ NAME ] cmd ... - Run cmd in the named network namespace
 .sp