ZTS: Test for clone, mmap and write for block cloning

For block cloning, if we mmap the cloned file and write from the
map into the file, it triggers a panic in dbuf_redirty() on Linux.

The same scenario causes data corruption on FreeBSD. Both these
issues are fixed under PR#15656 and PR#15665.

It would be good to add a test for this scenario in ZTS. The test
program and issue was produced by @robn.

Reviewed-by: Pawel Jakub Dawidek <pawel@dawidek.net>
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 #15717

tests/zfs-tests/tests/Makefile.am

@@ -461,6 +461,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/bclone/setup.ksh \
 	functional/block_cloning/cleanup.ksh \
 	functional/block_cloning/setup.ksh \
+	functional/block_cloning/block_cloning_clone_mmap_write.ksh \
 	functional/block_cloning/block_cloning_copyfilerange_cross_dataset.ksh \
 	functional/block_cloning/block_cloning_copyfilerange_fallback.ksh \
 	functional/block_cloning/block_cloning_copyfilerange_fallback_same_txg.ksh \

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

@@ -0,0 +1,79 @@
+#!/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
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/block_cloning/block_cloning.kshlib
+
+#
+# DESCRIPTION:
+#	A PANIC is triggered in dbuf_redirty() if we clone a file, mmap it
+#	and write from the map into the file. PR#15656 fixes this scenario.
+#	This scenario also causes data corruption on FreeBSD, which is fixed
+#	by PR#15665.
+#
+# STRATEGY:
+#	1. Create a pool
+#	2. Create a test file 
+#	3. Clone, mmap and write to the file using clone_mmap_write
+#	5. Synchronize cached writes
+#	6. Verfiy data is correctly written to the disk
+#
+
+verify_runnable "global"
+
+if is_linux && [[ $(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"
+
+function cleanup
+{
+	datasetexists $TESTPOOL && destroy_pool $TESTPOOL
+	rm -rf $VDIR
+}
+
+log_onexit cleanup
+
+log_assert "Test for clone, mmap and write scenario"
+
+log_must rm -rf $VDIR
+log_must mkdir -p $VDIR
+log_must truncate -s 1G $VDEV
+
+log_must zpool create -o feature@block_cloning=enabled $TESTPOOL $VDEV
+log_must zfs create $TESTPOOL/$TESTFS
+
+log_must dd if=/dev/urandom of=/$TESTPOOL/$TESTFS/file bs=1M count=512
+log_must clone_mmap_write /$TESTPOOL/$TESTFS/file /$TESTPOOL/$TESTFS/clone
+
+sync_pool $TESTPOOL
+log_must sync
+
+log_must have_same_content /$TESTPOOL/$TESTFS/file /$TESTPOOL/$TESTFS/clone
+blocks=$(get_same_blocks $TESTPOOL/$TESTFS file $TESTPOOL/$TESTFS clone)
+# FreeBSD's seq(1) leaves a trailing space, remove it with sed(1).
+log_must [ "$blocks" = "$(seq -s " " 1 4095 | sed 's/ $//')" ]
+
+log_pass "Clone, mmap and write does not cause data corruption or " \
+	"trigger panic"