generic: test cloning large exents to a file with many small extents

Test that if we clone a file with some large extents into a file
that has many small extents, when the fs is nearly full, the clone
operation does not fail and produces the correct result.

This is motivated by a bug found in btrfs wich is fixed by the
following patches for the linux kernel:

 [PATCH 1/2] Btrfs: factor out extent dropping code from hole punch handler
 [PATCH 2/2] Btrfs: fix ENOSPC errors, leading to transaction aborts, when
             cloning extents

The test currently passes on xfs.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/562

@@ -0,0 +1,78 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2019 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FSQA Test No. 562
+#
+# Test that if we clone a file with some large extents into a file that has
+# many small extents, when the fs is nearly full, the clone operation does
+# not fail and produces the correct result.
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+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
+
+# real QA test starts here
+_supported_fs generic
+_supported_os Linux
+_require_scratch_reflink
+_require_test_program "punch-alternating"
+_require_xfs_io_command "fpunch"
+
+rm -f $seqres.full
+
+_scratch_mkfs_sized $((512 * 1024 * 1024)) >>$seqres.full 2>&1
+_scratch_mount
+
+file_size=$(( 200 * 1024 * 1024 )) # 200Mb
+
+# Create a file with many small extents.
+$XFS_IO_PROG -f -c "pwrite -S 0xe5 -b $file_size 0 $file_size" \
+	$SCRATCH_MNT/foo >>/dev/null
+$here/src/punch-alternating $SCRATCH_MNT/foo >> $seqres.full
+
+# Create file bar with the same size that file foo has but with large extents.
+$XFS_IO_PROG -f -c "pwrite -S 0xc7 -b $file_size 0 $file_size" \
+	$SCRATCH_MNT/bar >>/dev/null
+
+# Fill the fs (For btrfs we are interested in filling all unallocated space
+# and most of the existing metadata block group(s), so that after this there
+# will be no unallocated space and metadata space will be mostly full but with
+# more than enough free space for the clone operation below to succeed, we
+# create files with 2Kb because that results in extents inlined in the metadata
+# (btree leafs) and it's the fastest way to fill metadata space on btrfs, by
+# default btrfs inlines up to 2Kb of data).
+i=1
+while true; do
+	$XFS_IO_PROG -f -c "pwrite 0 2K" $SCRATCH_MNT/filler_$i &> /dev/null
+	[ $? -ne 0 ] && break
+	i=$(( i + 1 ))
+done
+
+# Now clone file bar into file foo. This is supposed to succeed and not fail
+# with ENOSPC for example.
+_reflink $SCRATCH_MNT/bar $SCRATCH_MNT/foo >>$seqres.full
+
+# Unmount and mount the filesystem again to verify the operation was durably
+# persisted.
+_scratch_cycle_mount
+
+echo "File foo data after cloning and remount:"
+od -A d -t x1 $SCRATCH_MNT/foo
+
+status=0
+exit

tests/generic/562.out

@@ -0,0 +1,5 @@
+QA output created by 562
+File foo data after cloning and remount:
+0000000 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7 c7
+*
+209715200

tests/generic/group

@@ -564,3 +564,4 @@
 559 auto stress dedupe
 560 auto stress dedupe
 561 auto stress dedupe
+562 auto clone