zdb: add -B option to generate backup stream

This is more-or-less like `zfs send`, but specifying the snapshot by its
objset id for situations where it can't be referenced any other way.

Sponsored-By: Klara, Inc.
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: WHR <msl0000023508@gmail.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #14642

tests/zfs-tests/tests/Makefile.am

@@ -572,6 +572,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/cli_root/zdb/zdb_006_pos.ksh \
 	functional/cli_root/zdb/zdb_args_neg.ksh \
 	functional/cli_root/zdb/zdb_args_pos.ksh \
+	functional/cli_root/zdb/zdb_backup.ksh \
 	functional/cli_root/zdb/zdb_block_size_histogram.ksh \
 	functional/cli_root/zdb/zdb_checksum.ksh \
 	functional/cli_root/zdb/zdb_decompress.ksh \

tests/zfs-tests/tests/functional/cli_root/zdb/zdb_backup.ksh

@@ -0,0 +1,55 @@
+#!/bin/ksh
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023, Klara Inc.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+write_count=8
+blksize=131072
+
+tmpfile=$TEST_BASE_DIR/tmpfile
+
+function cleanup
+{
+	datasetexists $TESTPOOL && destroy_pool $TESTPOOL
+	rm $tmpfile.1 $tmpfile.2
+}
+
+log_onexit cleanup
+
+log_assert "Verify that zfs send and zdb -B produce the same stream"
+
+verify_runnable "global"
+verify_disk_count "$DISKS" 2
+
+default_mirror_setup_noexit $DISKS
+file_write -o create -w -f $TESTDIR/file -b $blksize -c $write_count
+
+snap=$TESTPOOL/$TESTFS@snap
+log_must zfs snapshot $snap
+typeset -i objsetid=$(zfs get -Ho value objsetid $snap)
+
+sync_pool $TESTPOOL
+
+log_must eval "zfs send -ecL $snap > $tmpfile.1"
+log_must eval "zdb -B $TESTPOOL/$objsetid ecL > $tmpfile.2"
+
+typeset sum1=$(cat $tmpfile.1 | md5sum)
+typeset sum2=$(cat $tmpfile.2 | md5sum)
+
+log_must test "$sum1" = "$sum2"
+
+log_pass "zfs send and zdb -B produce the same stream"