overlay: truncate running binaries from lower and upper dirs

Test truncate running executable binaries from lower and upper dirs.
truncate(2) should return ETXTBSY, not other errno nor segfault

Commit 03bea6040932 ("ovl: get_write_access() in truncate") fixed
this issue.

Reviewed-by: Xiong Zhou <xzhou@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/overlay/013

@@ -0,0 +1,74 @@
+#! /bin/bash
+# FS QA Test 013
+#
+# Test truncate running executable binaries from lower and upper dirs.
+# truncate(2) should return ETXTBSY, not other errno nor segfault
+#
+# Commit 03bea6040932 ("ovl: get_write_access() in truncate") fixed this issue.
+#-----------------------------------------------------------------------
+# Copyright (c) 2016 Red Hat Inc.  All Rights Reserved.
+#
+# 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"
+
+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 $seqres.full
+
+# real QA test starts here
+_supported_fs overlay
+_supported_os Linux
+_require_scratch
+_require_test_program "t_truncate_self"
+
+# remove all files from previous runs
+_scratch_mkfs
+
+# copy test program to lower and upper dir
+lowerdir=$SCRATCH_DEV/$OVERLAY_LOWER_DIR
+upperdir=$SCRATCH_DEV/$OVERLAY_UPPER_DIR
+mkdir -p $lowerdir
+mkdir -p $upperdir
+cp $here/src/t_truncate_self $lowerdir/test_lower
+cp $here/src/t_truncate_self $lowerdir/test_upper
+
+_scratch_mount
+
+# run test program from lower and upper dir
+# test programs truncate themselfs, all should fail with ETXTBSY
+$SCRATCH_MNT/test_lower
+$SCRATCH_MNT/test_upper
+
+# success, all done
+echo "Silence is golden"
+status=0
+exit