overlay: test hardlink breakage on copy up

Introduce a new test to demonstrate a known issue with overlayfs:
- file A and B are hardlinked in lower
- modify A to trigger copy up
- file A is no longer a hardlink of file B

There is no fix for this issue at this time.

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

tests/overlay/018

@@ -0,0 +1,89 @@
+#! /bin/bash
+# FSQA Test No. 018
+#
+# Test hardlink breakage
+#
+# This simple test demonstrates a known issue with overlayfs:
+# - file A and B are hardlinked in lower
+# - modify A to trigger copy up
+# - file A is no longer a hardlink of file B
+#
+#-----------------------------------------------------------------------
+#
+# Copyright (C) 2016 CTERA Networks. All Rights Reserved.
+# Author: Amir Goldstein <amir73il@gmail.com>
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+_supported_fs overlay
+_supported_os Linux
+_require_scratch
+
+rm -f $seqres.full
+
+_scratch_mkfs >>$seqres.full 2>&1
+
+# Create 2 hardlinked files in lower
+lowerdir=$SCRATCH_DEV/$OVERLAY_LOWER_DIR
+mkdir -p $lowerdir
+echo "patient zero" >> $lowerdir/foo
+ln $lowerdir/foo $lowerdir/bar
+
+
+_scratch_mount
+
+
+rm -f $tmp.before $tmp.after
+
+foo=$SCRATCH_MNT/foo
+bar=$SCRATCH_MNT/bar
+
+# Record inode number and nlink before copy up
+ls -li $foo $bar | awk '{ print $1, $3 }' > $tmp.before
+
+# Modify content of one of the hardlinks
+echo "mutated" >> $foo
+
+# Record inode number and nlink after copy up
+ls -li $foo $bar | awk '{ print $1, $3 }' > $tmp.after
+
+# Compare ino/nlink before..after - expect silence
+diff $tmp.before $tmp.after
+
+# Compare content of files - expect silence
+diff $foo $bar
+
+echo "Silence is golden"
+status=0
+exit

tests/overlay/018.out

@@ -0,0 +1,2 @@
+QA output created by 018
+Silence is golden

tests/overlay/group

@@ -20,3 +20,4 @@
 015 auto quick whiteout
 016 auto quick copyup
 017 auto quick copyup
+018 auto quick copyup