zdtm: check a case when a root of sub-mntns is read-only

It's what we have when ReadOnlyDirectories=/ is set for systemd services.
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm/static/Makefile

@@ -231,6 +231,7 @@ TST_DIR		=				\
 		mntns_open			\
 		mntns_link_remap		\
 		mntns_ghost			\
+		mntns_ro_root			\
 		mntns_link_ghost		\
 		mntns_shared_bind		\
 		mntns_shared_bind02		\

test/zdtm/static/mntns_ro_root.c

+#define _GNU_SOURCE
+#include <stdbool.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <signal.h>
+#include <stdio.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sched.h>
+#include <sys/wait.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <sys/mount.h>
+#include <dirent.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc	= "Check a case when a root is read-only for a sub-mntns";
+const char *test_author	= "Andrew Vagin <avagin@parallels.com>";
+
+char *dirname;
+TEST_OPTION(dirname, string, "directory name", 1);
+
+
+int main(int argc, char **argv)
+{
+	task_waiter_t lock;
+	pid_t pid = -1;
+	int status = 1;
+
+	task_waiter_init(&lock);
+	test_init(argc, argv);
+
+	pid = fork();
+	if (pid < 0) {
+		pr_perror("fork");
+		return 1;
+	}
+
+	if (pid == 0) {
+		if (unshare(CLONE_NEWNS)) {
+			pr_perror("unshare");
+			return 1;
+		}
+		if (mount(NULL, "/", NULL, MS_REMOUNT | MS_RDONLY | MS_BIND, NULL)) {
+			pr_perror("mount");
+			return 1;
+		}
+
+		task_waiter_complete(&lock, 1);
+		test_waitsig();
+
+		return 0;
+	}
+
+	task_waiter_wait4(&lock, 1);
+	test_daemon();
+	test_waitsig();
+
+	kill(pid, SIGTERM);
+	wait(&status);
+	if (status) {
+		fail("Test died");
+		return 1;
+	}
+	pass();
+
+	return 0;
+}

test/zdtm/static/mntns_ro_root.desc

+{'flavor': 'ns uns', 'flags': 'suid', 'feature': 'mnt_id'}