Introduce zfs rewrite subcommand (#17246)

This allows to rewrite content of specified file(s) as-is without
modifications, but at a different location, compression, checksum,
dedup, copies and other parameter values.  It is faster than read
plus write, since it does not require data copying to user-space.
It is also faster for sync=always datasets, since without data
modification it does not require ZIL writing.  Also since it is
protected by normal range range locks, it can be done under any
other load.  Also it does not affect file's modification time or
other properties.

Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>

tests/runfiles/common.run

@@ -306,6 +306,10 @@ tags = ['functional', 'cli_root', 'zfs_rename']
 tests = ['zfs_reservation_001_pos', 'zfs_reservation_002_pos']
 tags = ['functional', 'cli_root', 'zfs_reservation']
 
+[tests/functional/cli_root/zfs_rewrite]
+tests = ['zfs_rewrite']
+tags = ['functional', 'cli_root', 'zfs_rewrite']
+
 [tests/functional/cli_root/zfs_rollback]
 tests = ['zfs_rollback_001_pos', 'zfs_rollback_002_pos',
     'zfs_rollback_003_neg', 'zfs_rollback_004_neg']

tests/runfiles/sanity.run

@@ -194,6 +194,10 @@ tags = ['functional', 'cli_root', 'zfs_rename']
 tests = ['zfs_reservation_001_pos', 'zfs_reservation_002_pos']
 tags = ['functional', 'cli_root', 'zfs_reservation']
 
+[tests/functional/cli_root/zfs_rewrite]
+tests = ['zfs_rewrite']
+tags = ['functional', 'cli_root', 'zfs_rewrite']
+
 [tests/functional/cli_root/zfs_rollback]
 tests = ['zfs_rollback_003_neg', 'zfs_rollback_004_neg']
 tags = ['functional', 'cli_root', 'zfs_rollback']

tests/zfs-tests/tests/Makefile.am

@@ -863,6 +863,9 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/cli_root/zfs_reservation/setup.ksh \
 	functional/cli_root/zfs_reservation/zfs_reservation_001_pos.ksh \
 	functional/cli_root/zfs_reservation/zfs_reservation_002_pos.ksh \
+	functional/cli_root/zfs_rewrite/cleanup.ksh \
+	functional/cli_root/zfs_rewrite/setup.ksh \
+	functional/cli_root/zfs_rewrite/zfs_rewrite.ksh \
 	functional/cli_root/zfs_rollback/cleanup.ksh \
 	functional/cli_root/zfs_rollback/setup.ksh \
 	functional/cli_root/zfs_rollback/zfs_rollback_001_pos.ksh \

tests/zfs-tests/tests/functional/cli_root/zfs_rewrite/cleanup.ksh

@@ -0,0 +1,26 @@
+#!/bin/ksh -p
+# SPDX-License-Identifier: CDDL-1.0
+#
+# 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
+
+default_cleanup

tests/zfs-tests/tests/functional/cli_root/zfs_rewrite/setup.ksh

@@ -0,0 +1,28 @@
+#!/bin/ksh -p
+# SPDX-License-Identifier: CDDL-1.0
+#
+# 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
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+DISK=${DISKS%% *}
+
+default_setup $DISK

tests/zfs-tests/tests/functional/cli_root/zfs_rewrite/zfs_rewrite.ksh

@@ -0,0 +1,104 @@
+#!/bin/ksh -p
+# SPDX-License-Identifier: CDDL-1.0
+#
+# 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) 2025, iXsystems, Inc.
+#
+
+# DESCRIPTION:
+#	Verify zfs rewrite rewrites specified files blocks.
+#
+# STRATEGY:
+#	1. Create two files, one of which is in a directory.
+#	2. Save the checksums and block pointers.
+#	3. Rewrite part of the files.
+#	4. Verify checksums are the same.
+#	5. Verify block pointers of the rewritten part have changed.
+#	6. Rewrite all the files.
+#	7. Verify checksums are the same.
+#	8. Verify all block pointers have changed.
+
+. $STF_SUITE/include/libtest.shlib
+
+typeset tmp=$(mktemp)
+typeset bps=$(mktemp)
+typeset bps1=$(mktemp)
+typeset bps2=$(mktemp)
+
+function cleanup
+{
+	rm -rf $tmp $bps $bps1 $bps2 $TESTDIR/*
+}
+
+log_assert "zfs rewrite rewrites specified files blocks"
+
+log_onexit cleanup
+
+log_must zfs set recordsize=128k $TESTPOOL/$TESTFS
+
+log_must mkdir $TESTDIR/dir
+log_must dd if=/dev/urandom of=$TESTDIR/file1 bs=128k count=8
+log_must dd if=$TESTDIR/file1 of=$TESTDIR/dir/file2 bs=128k
+log_must sync_pool $TESTPOOL
+typeset orig_hash1=$(xxh128digest $TESTDIR/file1)
+typeset orig_hash2=$(xxh128digest $TESTDIR/dir/file2)
+
+log_must [ "$orig_hash1" = "$orig_hash2" ]
+log_must eval "zdb -Ovv $TESTPOOL/$TESTFS file1 > $tmp"
+log_must eval "awk '/ L0 / { print l++ \" \" \$3 }' < $tmp > $bps1"
+log_must eval "zdb -Ovv $TESTPOOL/$TESTFS dir/file2 > $tmp"
+log_must eval "awk '/ L0 / { print l++ \" \" \$3 }' < $tmp > $bps2"
+
+log_must zfs rewrite -o 327680 -l 262144 -r -x $TESTDIR/file1 $TESTDIR/dir/file2
+log_must sync_pool $TESTPOOL
+typeset new_hash1=$(xxh128digest $TESTDIR/file1)
+typeset new_hash2=$(xxh128digest $TESTDIR/dir/file2)
+log_must [ "$orig_hash1" = "$new_hash1" ]
+log_must [ "$orig_hash2" = "$new_hash2" ]
+
+log_must eval "zdb -Ovv $TESTPOOL/$TESTFS file1 > $tmp"
+log_must eval "awk '/ L0 / { print l++ \" \" \$3 }' < $tmp > $bps"
+typeset same=$(echo $(sort -n $bps $bps1 | uniq -d | cut -f1 -d' '))
+log_must [ "$same" = "0 1 5 6 7" ]
+log_must eval "zdb -Ovv $TESTPOOL/$TESTFS dir/file2 > $tmp"
+log_must eval "awk '/ L0 / { print l++ \" \" \$3 }' < $tmp > $bps"
+typeset same=$(echo $(sort -n $bps $bps2 | uniq -d | cut -f1 -d' '))
+log_must [ "$same" = "0 1 5 6 7" ]
+
+log_must zfs rewrite -r $TESTDIR/file1 $TESTDIR/dir/file2
+log_must sync_pool $TESTPOOL
+typeset new_hash1=$(xxh128digest $TESTDIR/file1)
+typeset new_hash2=$(xxh128digest $TESTDIR/dir/file2)
+log_must [ "$orig_hash1" = "$new_hash1" ]
+log_must [ "$orig_hash2" = "$new_hash2" ]
+
+log_must eval "zdb -Ovv $TESTPOOL/$TESTFS file1 > $tmp"
+log_must eval "awk '/ L0 / { print l++ \" \" \$3 }' < $tmp > $bps"
+typeset same=$(echo $(sort -n $bps $bps1 | uniq -d | cut -f1 -d' '))
+log_must [ -z "$same" ]
+log_must eval "zdb -Ovv $TESTPOOL/$TESTFS dir/file2 > $tmp"
+log_must eval "awk '/ L0 / { print l++ \" \" \$3 }' < $tmp > $bps"
+typeset same=$(echo $(sort -n $bps $bps2 | uniq -d | cut -f1 -d' '))
+log_must [ -z "$same" ]
+
+log_pass