test: check read-only bind-mounts

Here is a real example how it's used.

Cc:  Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Tested-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -323,6 +323,7 @@ mntns_link_ghost
 mntns_shared_bind
 mntns_shared_bind02
 mntns_root_bind
+mntns_rw_ro_rw
 sockets00
 cow01
 "

test/zdtm/live/static/Makefile

@@ -114,6 +114,7 @@ TST_NOFILE	=				\
 		stopped				\
 		rtc				\
 		clean_mntns			\
+		mntns_rw_ro_rw			\
 		dumpable01			\
 		dumpable02			\
 		remap_dead_pid			\

test/zdtm/live/static/mntns_rw_ro_rw.c

+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mount.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc	= "Test read-only bind mounts";
+const char *test_author	= "Andrey Vagin <xemul@parallels.com>";
+
+int main(int argc, char **argv)
+{
+	test_init(argc, argv);
+
+	if (mount("/proc/sys/", "/proc/sys", NULL, MS_BIND, NULL)) {
+		err("Unable to bind-mount  /proc/sys");
+		return 1;
+	}
+	if (mount("/proc/sys/net", "/proc/sys/net", NULL, MS_BIND, NULL)) {
+		err("Unable to bind-mount /proc/sys/net");
+		return 1;
+	}
+	if (mount("/proc/sys/", "/proc/sys", NULL, MS_RDONLY|MS_BIND|MS_REMOUNT, NULL)) {
+		err("Unable to remount  /proc/sys");
+		return 1;
+	}
+
+	test_daemon();
+	test_waitsig();
+
+	if (access("/proc/sys/net/unix/max_dgram_qlen", W_OK)) {
+		fail("Unable to access /proc/sys/net/core/wmem_max");
+		return 1;
+	}
+
+	if (access("/proc/sys/kernel/pid_max", W_OK) != -1 || errno != EROFS) {
+		fail("Unable to access /proc/sys/kernel/pid_max");
+		return 1;
+	}
+
+	pass();
+
+	return 0;
+}