overlay: Test unique st_dev;st_ino on non-samefs setup

Check that files from middle layer on same fs as upper layer
are not allowed to export the real inode st_dev;st_ino.

This is a regression test for kernel commit:
  9c6d8f13e9da ("ovl: fix corner case of non-unique st_dev;st_ino")

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/overlay/067

@@ -0,0 +1,94 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2019 CTERA Networks. All Rights Reserved.
+#
+# FSQA Test No. 067
+#
+# Test unique st_dev;st_ino on non-samefs setup.
+#
+# Check that files from middle layer on same fs as upper layer
+# are not allowed to export the real inode st_dev;st_ino.
+#
+# This is a regression test for kernel commit:
+#   9c6d8f13e9da ovl: fix corner case of non-unique st_dev;st_ino
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+rm -f $seqres.full
+
+# real QA test starts here
+_supported_fs overlay
+_supported_os Linux
+# Use non-default scratch underlying overlay dirs, we need to check
+# them explicity after test.
+_require_scratch_nocheck
+_require_test
+
+# Lower is on test partition
+lower=$OVL_BASE_TEST_DIR/$OVL_LOWER-$seq
+# Upper/work are on scratch partition
+middle=$OVL_BASE_SCRATCH_MNT/$OVL_LOWER
+upper=$OVL_BASE_SCRATCH_MNT/$OVL_UPPER
+work=$OVL_BASE_SCRATCH_MNT/$OVL_WORK
+
+rm -rf $lower
+mkdir $lower
+
+_scratch_mkfs >>$seqres.full 2>&1
+
+realfile=$middle/file
+testfile=$SCRATCH_MNT/file
+
+# Create a file on middle layer on same fs as upper layer
+echo wrong > $realfile
+
+# Mount an overlay on $SCRATCH_MNT with lower layer on test partition
+# and middle and upper layer on scratch partition.
+# Disable xino, so not all overlay inodes are on the same st_dev.
+_overlay_scratch_mount_dirs $middle:$lower $upper $work -o xino=off || \
+	_notrun "cannot mount overlay with xino=off option"
+
+stat $realfile >>$seqres.full
+stat $testfile >>$seqres.full
+
+# Diverge the content of the overlay file from its origin
+echo right > $testfile
+
+stat $testfile >>$seqres.full
+
+# Expect the overlay file to differ from the original lower file
+diff -q $realfile $testfile >>$seqres.full &&
+	echo "diff with middle layer file doesn't know right from wrong! (warm cache)"
+
+echo 3 > /proc/sys/vm/drop_caches
+
+stat $testfile >>$seqres.full
+
+# Expect the overlay file to differ from the original lower file
+diff -q $realfile $testfile >>$seqres.full &&
+	echo "diff with middle layer file doesn't know right from wrong! (cold cache)"
+
+$UMOUNT_PROG $SCRATCH_MNT
+# check overlayfs
+_overlay_check_scratch_dirs $middle:$lower $upper $work -o xino=off
+
+echo "Silence is golden"
+status=0
+exit

tests/overlay/067.out

@@ -0,0 +1,2 @@
+QA output created by 067
+Silence is golden

tests/overlay/group

@@ -69,3 +69,4 @@
 064 auto quick copyup
 065 auto quick mount
 066 auto quick copyup
+067 auto quick copyup nonsamefs