reflink: test unlinking a huge extent with a lot of refcount adjustments

Test a regression in XFS where we blow out a transaction reservation if
we create a big file, share every other block, and delete the first
file.  There's nothing particularly fs-specific about this stress test,
so put it in generic.

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

tests/generic/447

@@ -0,0 +1,94 @@
+#! /bin/bash
+# FS QA Test No. 447
+#
+# See how well we handle deleting a file with a million refcount extents.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2017, Oracle and/or its affiliates.  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".* $testdir/file1
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/attr
+. ./common/reflink
+
+# real QA test starts here
+_supported_os Linux
+_require_scratch_reflink
+_require_cp_reflink
+_require_test_program "punch-alternating"
+
+rm -f "$seqres.full"
+
+echo "Format and mount"
+_scratch_mkfs > "$seqres.full" 2>&1
+_scratch_mount >> "$seqres.full" 2>&1
+
+testdir="$SCRATCH_MNT/test-$seq"
+mkdir "$testdir"
+
+# Setup for one million blocks, but we'll accept stress testing down to
+# 2^17 blocks... that should be plenty for anyone.
+fnr=20
+free_blocks=$(stat -f -c '%a' "$testdir")
+blksz=$(_get_block_size "$testdir")
+space_avail=$((free_blocks * blksz))
+calc_space() {
+	blocks_needed=$(( 2 ** (fnr + 1) ))
+	space_needed=$((blocks_needed * blksz * 5 / 4))
+}
+calc_space
+while test $space_needed -gt $space_avail; do
+	fnr=$((fnr - 1))
+	calc_space
+done
+test $fnr -lt 17 && _notrun "Insufficient space for stress test; would only create $blocks_needed extents ($space_needed/$space_avail blocks)."
+
+echo "Create a many-block file"
+echo "creating $blocks_needed blocks..." >> "$seqres.full"
+$XFS_IO_PROG -f -c "pwrite -S 0x61 -b 4194304 0 $((2 ** (fnr + 1) * blksz))" "$testdir/file1" >> "$seqres.full"
+
+echo "Reflinking file"
+_cp_reflink $testdir/file1 $testdir/file2
+
+echo "Punch file2"
+echo "Punching file2..." >> "$seqres.full"
+"$here/src/punch-alternating" "$testdir/file2" >> "$seqres.full"
+echo "...done" >> "$seqres.full"
+_scratch_cycle_mount
+
+echo "Delete file1"
+rm -rf $testdir/file1
+
+# success, all done
+status=0
+exit