zdtm: add mnt_root_ext test

This test has one external mount [criumntns] /zdtm_root_ext.tmp ->
[testmntns] /mnt_root_ext.test, and it specifically gives '--external
mnt[MNT]:.zdtm_root_ext.tmp' option on restore without '/' to make
dirname on it return static '.' path (see glibc dirname() code) and
reproduce a segfault in resolve_mountpoint().

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>

test/zdtm/static/Makefile

@@ -402,6 +402,7 @@ TST_DIR		=				\
 		mnt_ext_master			\
 		mnt_ext_dev			\
 		mnt_ext_root			\
+		mnt_root_ext			\
 		mnt_ext_collision		\
 		mntns_pivot_root		\
 		mntns_pivot_root_ro		\

test/zdtm/static/mnt_root_ext.c

@@ -0,0 +1,79 @@
+#include <sched.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <linux/limits.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc = "Check external mount from host's rootfs";
+const char *test_author = "Pavel Tikhomirov <ptikhomirov@virtuozzo.com>";
+
+char *dirname = "mnt_root_ext.test";
+TEST_OPTION(dirname, string, "directory name", 1);
+
+int main(int argc, char **argv)
+{
+	char *root, testdir[PATH_MAX], nstestdir[PATH_MAX];
+	char *zdtm_newns = getenv("ZDTM_NEWNS");
+	char tmp[] = "/.zdtm_root_ext.tmp";
+
+	root = getenv("ZDTM_ROOT");
+	if (root == NULL) {
+		pr_perror("root");
+		return 1;
+	}
+
+	if (!zdtm_newns) {
+		pr_perror("ZDTM_NEWNS is not set");
+		return 1;
+	} else if (strcmp(zdtm_newns, "1")) {
+		goto test;
+	}
+
+	/* Prepare directories in test root */
+	sprintf(testdir, "%s/%s", root, dirname);
+	mkdir(testdir, 0755);
+
+	/* Prepare directories in criu root */
+	mkdir(tmp, 0755);
+
+	/* Make criu's mntns root mount shared */
+	if (mount(NULL, "/", NULL, MS_SHARED, NULL)) {
+		pr_perror("make shared");
+		return 1;
+	}
+
+	/*
+	 * Create temporary mntns, next mounts will not show up in criu mntns
+	 */
+	if (unshare(CLONE_NEWNS)) {
+		pr_perror("unshare");
+		return 1;
+	}
+
+	/*
+	 * Populate to the tests root host's rootfs subdir
+	 */
+	if (mount(tmp, testdir, NULL, MS_BIND, NULL)) {
+		pr_perror("bind");
+		return 1;
+	}
+test:
+	test_init(argc, argv);
+
+	/*
+	 * Make "external" mount to be slave
+	 */
+	sprintf(nstestdir, "/%s", dirname);
+	if (mount(NULL, nstestdir, NULL, MS_SLAVE, NULL)) {
+		pr_perror("make slave");
+		return 1;
+	}
+
+	test_daemon();
+	test_waitsig();
+
+	pass();
+
+	return 0;
+}

test/zdtm/static/mnt_root_ext.desc

@@ -0,0 +1,5 @@
+{   'dopts': '--external mnt[/mnt_root_ext.test]:MNT',
+    'feature': 'mnt_id move_mount_set_group',
+    'flavor': 'ns uns',
+    'flags': 'suid',
+    'ropts': '--external mnt[MNT]:.zdtm_root_ext.tmp --no-mntns-compat-mode'}

test/zdtm/static/mnt_root_ext.hook

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+[ "$1" == "--clean" ] || exit 0
+
+rmdir /.zdtm_root_ext.tmp