zstream: add a drop_record subcommand

It can be used to drop extraneous records in a send stream caused by a
corrupt dataset, as in issue #18239.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alan Somers <asomers@gmail.com>
Sponsored by:	ConnectWise
Closes #18275

tests/runfiles/common.run

@@ -998,7 +998,8 @@ tests = ['recv_dedup', 'recv_dedup_encrypted_zvol', 'rsend_001_pos',
     'send_encrypted_props', 'send_encrypted_truncated_files',
     'send_freeobjects', 'send_realloc_files', 'send_realloc_encrypted_files',
     'send_spill_block', 'send_holds', 'send_hole_birth', 'send_mixed_raw',
-    'send-wR_encrypted_zvol', 'send_partial_dataset', 'send_invalid',
+    'send-wR_encrypted_zvol', 'send-zstream_drop_record',
+    'send_partial_dataset', 'send_invalid',
     'send_large_blocks_incremental', 'send_large_blocks_initial',
     'send_large_microzap_incremental', 'send_large_microzap_transitive',
     'send_doall', 'send_raw_spill_block', 'send_raw_ashift',

tests/zfs-tests/tests/Makefile.am

@@ -2094,6 +2094,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/rsend/send_realloc_files.ksh \
 	functional/rsend/send_spill_block.ksh \
 	functional/rsend/send-wR_encrypted_zvol.ksh \
+	functional/rsend/send-zstream_drop_record.ksh \
 	functional/rsend/setup.ksh \
 	functional/scrub_mirror/cleanup.ksh \
 	functional/scrub_mirror/scrub_mirror_001_pos.ksh \

tests/zfs-tests/tests/functional/rsend/send-zstream_drop_record.ksh

@@ -0,0 +1,79 @@
+#!/bin/ksh -p
+# SPDX-License-Identifier: CDDL-1.0
+
+#
+# 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) 2026 by ConnectWise. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/rsend/rsend.kshlib
+. $STF_SUITE/include/math.shlib
+
+#
+# Description:
+# Verify that "zstream drop_record" can remove a record from a stream
+#
+# Strategy:
+# 1. Create a file containing multiple records, both full size and embedded.
+# 2. Send the dataset and drop some records
+# 3. Verify the dropped records are no longer present
+# 4. Verify that "zfs recv" can still receive the dataset.
+
+verify_runnable "both"
+
+log_assert "Verify zstream drop_record correctly drops records."
+log_onexit cleanup_pool $POOL2
+
+typeset sendfs=$POOL2/fs
+typeset recvfs=$POOL2/fs2
+typeset stream=$BACKDIR/stream
+typeset filtered=$BACKDIR/filtered
+typeset dump=$BACKDIR/dump
+
+log_must zfs create -o compress=lz4 $sendfs
+typeset dir=$(get_prop mountpoint $sendfs)
+
+truncate -s 1m $dir/full_records
+# Create some full size records
+log_must dd if=/dev/urandom of=$dir/full_records conv=notrunc bs=128k count=2
+
+# Create a file with an embedded record.  I don't know how to create a file
+# with two embedded records.
+recsize=16384
+# For lz4, this method works for blocks up to 16k, but not larger
+[[ $recsize -eq $((32 * 1024)) ]] && break
+if is_illumos; then
+	log_must mkholes -h 0:$((recsize - 8)) -d $((recsize - 8)):8 \
+	    $dir/embedded_records
+else
+	log_must truncate -s 16384 $dir/embedded_records
+	log_must dd if=/dev/urandom of=$dir/embedded_records \
+	    seek=$((recsize - 8)) bs=1 count=8 conv=notrunc
+fi
+
+log_must zfs snapshot $sendfs@snap
+typeset inode1=$(get_objnum $dir/full_records)
+typeset inode2=$(get_objnum $dir/embedded_records)
+
+# Verify that the requested records, and only them, were dropped
+log_must eval "zfs send -ce $sendfs@snap > $stream"
+log_must eval "zstream drop_record $inode1,131072 $inode2,0 < $stream > $filtered"
+log_must eval "zstream dump -v < $filtered > $dump"
+log_must grep -qE "^WRITE object = $inode1\>.*offset = 0" $dump
+log_mustnot grep -qE "^WRITE object = $inode1\>.*offset = 131072" $dump
+log_mustnot grep -qE "^WRITE_EMBEDDED object = $inode2\>.*offset = 0" $dump
+
+# Verify that the stream can be received
+log_must eval "zfs recv $recvfs < $stream"
+
+log_pass "zstream drop_record correctly drops records."