Allow opt-in of zvol blocks in special class

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Signed-off-by: Don Brady <dev.fs.zfs@gmail.com>
Closes #14876

tests/zfs-tests/tests/Makefile.am

@@ -429,6 +429,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/alloc_class/alloc_class_013_pos.ksh \
 	functional/alloc_class/alloc_class_014_neg.ksh \
 	functional/alloc_class/alloc_class_015_pos.ksh \
+	functional/alloc_class/alloc_class_016_pos.ksh \
 	functional/alloc_class/cleanup.ksh \
 	functional/alloc_class/setup.ksh \
 	functional/append/file_append.ksh \

tests/zfs-tests/tests/functional/alloc_class/alloc_class_016_pos.ksh

@@ -0,0 +1,60 @@
+#!/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.
+#
+
+. $STF_SUITE/tests/functional/alloc_class/alloc_class.kshlib
+
+#
+# DESCRIPTION:
+#	File blocks and zvol blocks, where special_small_blocks is active,
+#	are expected to end up in the special class.
+#
+
+verify_runnable "global"
+
+claim="File and zvol blocks using special_small_blocks end up in special class"
+
+log_assert $claim
+log_onexit cleanup
+log_must disk_setup
+
+log_must zpool create $TESTPOOL $ZPOOL_DISKS special $CLASS_DISK0
+
+# Provision a filesystem with special_small_blocks and copy 10M to it
+log_must zfs create -o compression=off -o special_small_blocks=32K \
+	-o recordsize=32K $TESTPOOL/$TESTFS
+log_must dd if=/dev/urandom of=/$TESTPOOL/$TESTFS/testfile bs=1M count=10
+
+# Provision a volume with special_small_blocks and copy 10M to it
+log_must zfs create -V 100M -b 32K -o special_small_blocks=32K \
+	-o compression=off $TESTPOOL/$TESTVOL
+block_device_wait "$ZVOL_DEVDIR/$TESTPOOL/$TESTVOL"
+log_must dd if=/dev/urandom of=$ZVOL_DEVDIR/$TESTPOOL/$TESTVOL bs=1M count=10
+
+sync_pool $TESTPOOL
+zpool list -v $TESTPOOL
+
+# Get the amount allocated to special vdev using vdev 'allocated' property
+result=$(zpool get -Hp allocated $TESTPOOL $CLASS_DISK0)
+set -- $result
+allocated=$3
+echo $allocated bytes allocated on special device $CLASS_DISK0
+
+# Confirm that at least 20M was allocated
+if [[ $allocated -lt 20971520 ]]
+then
+	log_fail "$allocated on special vdev $CLASS_DISK0, but expecting 20M"
+fi
+
+log_must zpool destroy -f "$TESTPOOL"
+log_pass $claim