generic: test reflinked file corruption after short COW

This test essentially creates an existing COW extent which
covers the first 1M, and then does another IO that overlaps it,
but extends beyond it.  The bug was that we did not trim the
new IO to the end of the existing COW extent, and so the IO
extended past the COW blocks and corrupted the reflinked files(s).

The bug came and went upstream.  It was introduced by:

78f0cc9d55cb "xfs: don't use delalloc extents for COW on files with extsize hints"
and (inadvertently) fixed as of:
36adcbace24e "xfs: fill out the srcmap in iomap_begin"
upstream, and in the 5.4 stable tree with:
aee38af574a1 "xfs: trim IO to found COW extent limit"

[Eryu: discard outputs of xfs_io when setting [cow]extsize]

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/612

@@ -0,0 +1,85 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2020 Red Hat, Inc.  All Rights Reserved.
+#
+# FS QA Test 612
+#
+# Regression test for reflink corruption present as of:
+# 78f0cc9d55cb "xfs: don't use delalloc extents for COW on files with extsize hints"
+# and (inadvertently) fixed as of:
+# 36adcbace24e "xfs: fill out the srcmap in iomap_begin"
+# upstream, and in the 5.4 stable tree with:
+# aee38af574a1 "xfs: trim IO to found COW extent limit"
+#
+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.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/reflink
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs generic
+_require_test
+_require_test_reflink
+
+DIR=$TEST_DIR/dir.$seq
+mkdir -p $DIR
+rm -f $DIR/a $DIR/b
+
+# This test essentially creates an existing COW extent which
+# covers the first 1M, and then does another IO that overlaps it,
+# but extends beyond it.  The bug was that we did not trim the
+# new IO to the end of the existing COW extent, and so the IO
+# extended past the COW blocks and corrupted the reflinked files(s).
+
+# Make all files w/ 1m hints; create original 2m file
+$XFS_IO_PROG -c "extsize 1048576" $DIR >/dev/null 2>&1
+$XFS_IO_PROG -c "cowextsize 1048576" $DIR >/dev/null 2>&1
+
+echo "Create file b"
+$XFS_IO_PROG -f -c "pwrite -S 0x0 0 2m" -c fsync $DIR/b | _filter_xfs_io
+
+# Make a reflinked copy
+echo "Reflink copy from b to a"
+cp --reflink=always $DIR/b $DIR/a
+
+echo "Contents of b"
+hexdump -C $DIR/b
+
+# Cycle mount to get stuff out of cache
+_test_cycle_mount
+
+# Create a 1m-hinted IO at offset 0, then
+# do another IO that overlaps but extends past the 1m hint
+echo "Write to a"
+$XFS_IO_PROG -c "pwrite -S 0xa 0k -b 4k 4k" \
+       -c "pwrite -S 0xa 4k -b 1m 1m" \
+       $DIR/a | _filter_xfs_io
+
+$XFS_IO_PROG -c fsync $DIR/a
+
+echo "Contents of b now:"
+hexdump -C $DIR/b
+
+# success, all done
+status=0
+exit

tests/generic/612.out

@@ -0,0 +1,18 @@
+QA output created by 612
+Create file b
+wrote 2097152/2097152 bytes at offset 0
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Reflink copy from b to a
+Contents of b
+00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+00200000
+Write to a
+wrote 4096/4096 bytes at offset 0
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 1048576/1048576 bytes at offset 4096
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Contents of b now:
+00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+*
+00200000

tests/generic/group

@@ -614,3 +614,4 @@
 609 auto quick rw
 610 auto quick prealloc zero
 611 auto quick attr
+612 auto quick clone