generic: add test to verify xattr replace operations are atomic

This test verifies that replacing a xattr's value is an atomic
operation. This is motivated by an issue in btrfs where replacing
a xattr's value wasn't an atomic operation, it consisted of
removing the old value and then inserting the new value in a
btree. This made readers (getxattr and listxattrs) not getting
neither the old nor the new value during a short time window.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

tests/generic/037

@@ -0,0 +1,102 @@
+#! /bin/bash
+# FSQA Test No. 037
+#
+# Verify that replacing a xattr's value is an atomic operation.
+# This is motivated by an issue in btrfs where replacing a xattr's value
+# wasn't an atomic operation, it consisted of removing the old value and
+# then inserting the new value in a btree. This made readers (getxattr
+# and listxattrs) not getting neither the old nor the new value during
+# a short time window.
+#
+# The btrfs issue was fixed by the following linux kernel patch:
+#
+#    Btrfs: make xattr replace operations atomic
+#
+#-----------------------------------------------------------------------
+#
+# Copyright (C) 2014 SUSE Linux Products GmbH. All Rights Reserved.
+# Author: Filipe Manana <fdmanana@suse.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()
+{
+	kill $setter_pid
+	rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/attr
+
+# real QA test starts here
+_need_to_be_root
+_supported_fs generic
+_supported_os Linux
+_require_scratch
+_require_attrs
+
+rm -f $seqres.full
+
+xattr_name="user.something"
+xattr_value1="foobar"
+xattr_value2="rabbit_hole"
+
+set_xattr_loop()
+{
+	local name=$1
+	local cur_val=$xattr_value1
+	while true; do
+		$SETFATTR_PROG -n $xattr_name -v $cur_val $SCRATCH_MNT/$name
+		if [ "$cur_val" == "$xattr_value1" ]; then
+			cur_val=$xattr_value2
+		else
+			cur_val=$xattr_value1
+		fi
+	done
+}
+
+value_filter()
+{
+	grep "$xattr_name=" | cut -d '=' -f 2 | \
+		sed -e "s/$xattr_value1/GOOD/" -e "s/$xattr_value2/GOOD/"
+}
+
+_scratch_mkfs >>$seqres.full 2>&1
+_scratch_mount
+
+test_file="test_xattr_replace"
+touch $SCRATCH_MNT/$test_file
+$SETFATTR_PROG -n $xattr_name -v $xattr_value1 $SCRATCH_MNT/$test_file
+
+set_xattr_loop $test_file &
+setter_pid=$!
+
+for ((i = 0; i < 1000; i++)); do
+	$GETFATTR_PROG --absolute-names -n $xattr_name \
+		$SCRATCH_MNT/$test_file | value_filter
+done
+
+status=0
+exit

tests/generic/group

@@ -39,6 +39,7 @@
 034 auto quick metadata log
 035 auto quick
 036 auto aio rw stress
+037 metadata auto quick
 053 acl repair auto quick
 062 attr udf auto quick
 068 other auto freeze dangerous stress