reflink: change block sharing with constant refcount

Ensure that we can handle the case where the refcount stays the same
even though the actual sharers changes.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/generic/359

@@ -0,0 +1,94 @@
+#! /bin/bash
+# FS QA Test No. 359
+#
+# Make sure that the reference counting mechanism can handle the case
+# where we share the first 1/4 of an extent with a file, share the
+# last 1/4 of the extent with a second file, share the first half of
+# the extent with N files, and share the second half of the extent
+# with a different set of N files.  The key point here is to test that
+# we handle the case where a refcount extent record doesn't coincide
+# exactly with the block mapping records.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2016 Oracle, 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 7 15
+
+_cleanup()
+{
+	cd /
+	rm -rf $tmp.*
+	wait
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/reflink
+
+# real QA test starts here
+_supported_os Linux
+_require_scratch_reflink
+
+echo "Format and mount"
+_scratch_mkfs > $seqres.full 2>&1
+_scratch_mount >> $seqres.full 2>&1
+
+testdir=$SCRATCH_MNT/test-$seq
+mkdir $testdir
+
+blocks=64
+blksz=65536
+nr=4
+halfway=$((blocks / 2 * blksz))
+quarter=$((blocks / 4 * blksz))
+
+echo "Initialize file"
+_pwrite_byte 0x61 0 $((blocks * blksz)) $testdir/file >> $seqres.full
+
+echo "Share the first half of the extent"
+seq 1 $nr | while read nr; do
+	_reflink_range $testdir/file 0 $testdir/file$nr.0 0 $halfway >> $seqres.full
+done
+
+echo "Share the last half of the extent"
+seq 1 $nr | while read nr; do
+	_reflink_range $testdir/file $halfway $testdir/file$nr.1 0 $halfway >> $seqres.full
+done
+
+echo "Share the first quarter of the extent"
+_reflink_range $testdir/file 0 $testdir/file.2 0 $quarter >> $seqres.full
+
+echo "Share the last quarter of the extent"
+_reflink_range $testdir/file $((quarter * 3)) $testdir/file.3 0 $quarter >> $seqres.full
+
+_scratch_cycle_mount
+
+echo "Check output"
+md5sum $testdir/file $testdir/file* | _filter_scratch
+
+# success, all done
+status=0
+exit