xfstests: btrfs/017: add a regression test for snapshot creation

We had a regression where you couldn't snapshot a file system if you mounted it
ro and then remounted it rw.  This is a test that does just that to make sure we
don't have this problem again.  I ran the test without the fix and it blew up,
and then applied the fix and verified that it passed.  Thanks,

Reviewed-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>

tests/btrfs/017

@@ -0,0 +1,61 @@
+#! /bin/bash
+# FS QA Test No. btrfs/017
+#
+# Regression test to make sure we can create a snapshot after mounting with
+# readonly and remounting rw.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2013 Fusion IO.  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!
+
+_cleanup()
+{
+	rm -f $tmp.*
+}
+
+trap "_cleanup ; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+_supported_fs btrfs
+_supported_os Linux
+_require_scratch
+
+rm -f $seqres.full
+
+_scratch_mkfs > /dev/null 2>&1
+_scratch_mount -o ro
+_scratch_mount -o rw,remount
+
+$BTRFS_UTIL_PROG sub snap $SCRATCH_MNT $SCRATCH_MNT/snap >> $seqres.full 2>&1 \
+	|| _fail "couldn't create snapshot"
+
+echo "Silence is golden"
+status=0 ; exit

tests/btrfs/017.out

@@ -0,0 +1,2 @@
+QA output created by 017
+Silence is golden

tests/btrfs/group

@@ -19,3 +19,4 @@
 014 auto
 015 auto quick
 016 auto quick
+017 auto quick