test: Add test for tempfs mount with open file

This test fails when run in ns:

(00.300947)      1: Error (util.c:568): exited, status=1
(00.300964)      1: Error (cr-restore.c:1067): 5 exited, status=1
(00.300989)      1: Error (mount.c:637): Can't restore tmpfs content
(00.301005) Error (cr-restore.c:1602): Restoring FAILED.

Reason for failure -- tar is spawned in new mount namespace where
it can not be found (bug #2870).
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -150,6 +150,7 @@ tun
 chroot
 chroot-file
 rtc
+tempfs
 "
 
 source $(readlink -f `dirname $0`/env.sh) || exit 1

test/zdtm/live/static/Makefile

@@ -144,6 +144,7 @@ TST_DIR		=				\
 		overmount_file			\
 		overmount_fifo			\
 		overmount_sock			\
+		tempfs				\
 
 TST_DIR_FILE	=				\
 		chroot				\

test/zdtm/live/static/tempfs.c

+#include <stdbool.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc	= "Check tmpfs mount";
+const char *test_author	= "Pavel Emelianov <xemul@parallels.com>";
+
+char *dirname;
+TEST_OPTION(dirname, string, "directory name", 1);
+
+#define TEST_WORD	"testtest"
+
+int main(int argc, char **argv)
+{
+	int fd, ret = 1;
+	char buf[1024];
+
+	test_init(argc, argv);
+
+	mkdir(dirname, 0700);
+	if (mount("none", dirname, "tmpfs", 0, "") < 0) {
+		fail("Can't mount tmpfs");
+		return 1;
+	}
+
+	snprintf(buf, sizeof(buf), "%s/test", dirname);
+	fd = open(buf, O_RDWR | O_CREAT);
+	if (fd < 0) {
+		err("open failed");
+		goto outum;
+	}
+
+	if (write(fd, TEST_WORD, sizeof(TEST_WORD)) != sizeof(TEST_WORD)) {
+		err("write() failed");
+		goto outuc;
+	}
+
+	test_daemon();
+	test_waitsig();
+
+	if (lseek(fd, 0, SEEK_SET) < 0) {
+		fail("Seek failed");
+		goto outuc;
+	}
+
+	buf[sizeof(TEST_WORD) + 1] = '\0';
+	if (read(fd, buf, sizeof(TEST_WORD)) != sizeof(TEST_WORD)) {
+		fail("Read failed");
+		goto outuc;
+	}
+
+	if (strcmp(buf, TEST_WORD)) {
+		fail("File corrupted");
+		goto outuc;
+	}
+
+	pass();
+	ret = 0;
+outuc:
+	close(fd);
+outum:
+	umount(dirname);
+	rmdir(dirname);
+	return ret;
+}