generic: test full dm snapshot devices

Full DM snapshot devices can return unexpected errors from the
underlying device, and this causes problems for filesystems.  In
particular, xfs used to panic in this test, (fixed by commit 8d6c121
"xfs: fix buffer use after free on IO error"), and on current
4.0-rc3 kernels both ext4 and btrfs trigger WARNINGs.

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

tests/generic/081

@@ -0,0 +1,86 @@
+#! /bin/bash
+# FS QA Test No. 081
+#
+# Test I/O error path by fully filling an dm snapshot.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2015 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.*
+	# lvm may have umounted it on I/O error, but in case it does not
+	$UMOUNT_PROG $mnt >/dev/null 2>&1
+	$LVM_PROG vgremove -f $vgname >>$seqres.full 2>&1
+	$LVM_PROG pvremove -f $SCRATCH_DEV >>$seqres.full 2>&1
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+_supported_fs generic
+_supported_os Linux
+_require_test
+_require_scratch_nocheck
+_require_dm_snapshot
+_require_block_device $SCRATCH_DEV
+_require_command $LVM_PROG lvm
+
+echo "Silence is golden"
+rm -f $seqres.full
+
+vgname=vg_$seq
+lvname=base_$seq
+snapname=snap_$seq
+mnt=$TEST_DIR/mnt_$seq
+mkdir -p $mnt
+
+# make sure there's enough disk space for 256M lv, test for 300M here in case
+# lvm uses some space for metadata
+_scratch_mkfs_sized $((300 * 1024 * 1024)) >>$seqres.full 2>&1
+$LVM_PROG vgcreate -f $vgname $SCRATCH_DEV >>$seqres.full 2>&1
+$LVM_PROG lvcreate --yes -L 256M -n $lvname $vgname >>$seqres.full 2>&1
+
+# _mkfs_dev exits the test on failure, this can make sure lv is created in
+# above vgcreate/lvcreate steps
+_mkfs_dev /dev/mapper/$vgname-$lvname
+
+# create a 4M snapshot
+$LVM_PROG lvcreate -s -L 4M -n $snapname $vgname/$lvname >>$seqres.full 2>&1 || \
+	_fail "Failed to create snapshot"
+
+_mount /dev/mapper/$vgname-$snapname $mnt
+
+# write 5M data to the snapshot
+$XFS_IO_PROG -fc "pwrite 0 5m" -c fsync $mnt/testfile >>$seqres.full 2>&1
+
+# _check_dmesg will check for WARNINGs/BUGs in dmesg
+status=0
+exit