Test LWB buffer overflow for block cloning

PR#15634 removes 128K into 2x68K LWB split optimization, since it
was found to cause LWB buffer overflow while trying to write 128KB
TX_CLONE_RANGE record with 1022 block pointers into 68KB buffer,
with multiple VDEVs ZIL.

This commit adds a test for this particular scenario by writing
maximum sizes TX_CLONE_RANE record with 1022 block pointers into
68KB buffer, with two SLOG devices.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by:  Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Signed-off-by: Umer Saleem <usaleem@ixsystems.com>
Closes openzfs#15672

tests/runfiles/linux.run

@@ -44,7 +44,8 @@ tests = ['block_cloning_copyfilerange', 'block_cloning_copyfilerange_partial',
     'block_cloning_copyfilerange_cross_dataset',
     'block_cloning_cross_enc_dataset',
     'block_cloning_copyfilerange_fallback_same_txg',
-    'block_cloning_replay', 'block_cloning_replay_encrypted']
+    'block_cloning_replay', 'block_cloning_replay_encrypted',
+    'block_cloning_lwb_buffer_overflow']
 tags = ['functional', 'block_cloning']
 
 [tests/functional/chattr:Linux]

tests/test-runner/bin/zts-report.py.in

@@ -305,6 +305,8 @@ elif sys.platform.startswith('linux'):
             ['SKIP', cfr_reason],
         'block_cloning/block_cloning_replay_encrypted':
             ['SKIP', cfr_reason],
+        'block_cloning/block_cloning_lwb_buffer_overflow':
+            ['SKIP', cfr_reason],
         'block_cloning/block_cloning_copyfilerange_cross_dataset':
             ['SKIP', cfr_cross_reason],
         'block_cloning/block_cloning_copyfilerange_fallback_same_txg':

tests/zfs-tests/tests/Makefile.am

@@ -454,6 +454,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/block_cloning/block_cloning_cross_enc_dataset.ksh \
 	functional/block_cloning/block_cloning_replay.ksh \
 	functional/block_cloning/block_cloning_replay_encrypted.ksh \
+	functional/block_cloning/block_cloning_lwb_buffer_overflow.ksh \
 	functional/bootfs/bootfs_001_pos.ksh \
 	functional/bootfs/bootfs_002_neg.ksh \
 	functional/bootfs/bootfs_003_pos.ksh \

tests/zfs-tests/tests/functional/block_cloning/block_cloning_lwb_buffer_overflow.ksh

@@ -0,0 +1,89 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or https://opensource.org/licenses/CDDL-1.0.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2023 by iXsystems, Inc. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/block_cloning/block_cloning.kshlib
+
+#
+# DESCRIPTION:
+#	Test for LWB buffer overflow with multiple VDEVs ZIL when 128KB
+#	block write is split into two 68KB ones, trying to write maximum
+#	sizes 128KB TX_CLONE_RANGE record with 1022 block pointers into
+#	68KB buffer.
+#
+# STRATEGY:
+#	1. Create a pool with multiple VDEVs ZIL
+#	2. Write maximum sizes TX_CLONE_RANGE record with 1022 block
+#	   pointers into 68KB buffer
+#	3. Sync TXG
+#	4. Clone the file
+#	5. Synchronize cached writes
+#
+
+verify_runnable "global"
+
+if [[ $(linux_version) -lt $(linux_version "4.5") ]]; then
+  log_unsupported "copy_file_range not available before Linux 4.5"
+fi
+
+VDIR=$TEST_BASE_DIR/disk-bclone
+VDEV="$VDIR/a $VDIR/b $VDIR/c"
+LDEV="$VDIR/e $VDIR/f"
+
+function cleanup
+{
+	datasetexists $TESTPOOL && destroy_pool $TESTPOOL
+	rm -rf $VDIR
+}
+
+log_onexit cleanup
+
+log_assert "Test for LWB buffer overflow with multiple VDEVs ZIL"
+
+log_must rm -rf $VDIR
+log_must mkdir -p $VDIR
+log_must truncate -s $MINVDEVSIZE $VDEV $LDEV
+
+log_must zpool create -o feature@block_cloning=enabled $TESTPOOL $VDEV \
+	log mirror $LDEV
+log_must zfs create -o recordsize=32K $TESTPOOL/$TESTFS
+# Each ZIL log entry can fit 130816 bytes for a block cloning operation,
+# so it can store 1022 block pointers. When LWB optimization is enabled,
+# an assert is hit when 128KB block write is split into two 68KB ones
+# for 2 SLOG devices
+log_must dd if=/dev/urandom of=/$TESTPOOL/$TESTFS/file1 bs=32K count=1022 \
+	conv=fsync
+sync_pool $TESTPOOL
+log_must clonefile -c /$TESTPOOL/$TESTFS/file1 /$TESTPOOL/$TESTFS/file2
+log_must sync
+
+sync_pool $TESTPOOL
+log_must have_same_content /$TESTPOOL/$TESTFS/file1 /$TESTPOOL/$TESTFS/file2
+typeset blocks=$(get_same_blocks $TESTPOOL/$TESTFS file1 $TESTPOOL/$TESTFS file2)
+log_must [ "$blocks" = "$(seq -s " " 0 1021)" ]
+
+log_pass "LWB buffer overflow is not triggered with multiple VDEVs ZIL"
+