Fix "snapdev" property inheritance behaviour

When inheriting the "snapdev" property to we don't always call
zfs_prop_set_special(): this prevents device nodes from being created in
certain situations. Because "snapdev" is the only *special* property
that is also inheritable we need to call zfs_prop_set_special() even
when we're not reverting it to the received value ('zfs inherit -S').

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #6131

tests/runfiles/linux.run

@@ -564,7 +564,8 @@ tests = ['zvol_cli_001_pos', 'zvol_cli_002_pos', 'zvol_cli_003_neg']
 
 [tests/functional/zvol/zvol_misc]
 tests = ['zvol_misc_001_neg', 'zvol_misc_002_pos', 'zvol_misc_003_neg',
-    'zvol_misc_004_pos', 'zvol_misc_005_neg', 'zvol_misc_006_pos']
+    'zvol_misc_004_pos', 'zvol_misc_005_neg', 'zvol_misc_006_pos',
+    'zvol_misc_snapdev']
 
 [tests/functional/zvol/zvol_swap]
 tests = ['zvol_swap_001_pos', 'zvol_swap_002_pos', 'zvol_swap_003_pos',

tests/zfs-tests/tests/functional/zvol/zvol_misc/Makefile.am

@@ -7,4 +7,5 @@ dist_pkgdata_SCRIPTS = \
 	zvol_misc_003_neg.ksh \
 	zvol_misc_004_pos.ksh \
 	zvol_misc_005_neg.ksh \
-	zvol_misc_006_pos.ksh
+	zvol_misc_006_pos.ksh \
+	zvol_misc_snapdev.ksh

tests/zfs-tests/tests/functional/zvol/zvol_misc/zvol_misc_snapdev.ksh

@@ -0,0 +1,159 @@
+#!/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 http://www.opensolaris.org/os/licensing.
+# 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 2017, loli10K <ezomori.nozomu@gmail.com>. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/cli_root/zfs_set/zfs_set_common.kshlib
+. $STF_SUITE/tests/functional/zvol/zvol_common.shlib
+
+#
+# DESCRIPTION:
+# Verify that ZFS volume property "snapdev" works as intended.
+#
+# STRATEGY:
+# 1. Verify "snapdev" property does not accept invalid values
+# 2. Verify "snapdev" adds and removes device nodes when updated
+# 3. Verify "snapdev" is inherited correctly
+#
+
+verify_runnable "global"
+
+function cleanup
+{
+	datasetexists $VOLFS && log_must zfs destroy -r $VOLFS
+	datasetexists $ZVOL && log_must zfs destroy -r $ZVOL
+	log_must zfs inherit snapdev $TESTPOOL
+	block_device_wait
+}
+
+#
+# Verify $device exists and is a block device
+#
+function blockdev_exists # device
+{
+	typeset device="$1"
+
+	if [[ ! -b "$device" ]]; then
+		log_fail "$device does not exist as a block device"
+	fi
+}
+
+#
+# Verify $device does not exist
+#
+function check_missing # device
+{
+	typeset device="$1"
+
+	if [[ -e "$device" ]]; then
+		log_fail "$device exists when not expected"
+	fi
+}
+
+#
+# Verify $property on $dataset is inherited by $parent and is set to $value
+#
+function verify_inherited # property value dataset parent
+{
+	typeset property="$1"
+	typeset value="$2"
+	typeset dataset="$3"
+	typeset parent="$4"
+
+	typeset val=$(get_prop "$property" "$dataset")
+	typeset src=$(get_source "$property" "$dataset")
+	if [[ "$val" != "$value" || "$src" != "inherited from $parent" ]]
+	then
+		log_fail "Dataset $dataset did not inherit $property properly:"\
+		    "expected=$value, value=$val, source=$src."
+	fi
+
+}
+
+log_assert "Verify that ZFS volume property 'snapdev' works as expected."
+log_onexit cleanup
+
+VOLFS="$TESTPOOL/volfs"
+ZVOL="$TESTPOOL/vol"
+SNAP="$ZVOL@snap"
+SNAPDEV="${ZVOL_DEVDIR}/$SNAP"
+SUBZVOL="$VOLFS/subvol"
+SUBSNAP="$SUBZVOL@snap"
+SUBSNAPDEV="${ZVOL_DEVDIR}/$SUBSNAP"
+
+log_must zfs create -o mountpoint=none $VOLFS
+log_must zfs create -V $VOLSIZE -s $ZVOL
+log_must zfs create -V $VOLSIZE -s $SUBZVOL
+
+# 1. Verify "snapdev" property does not accept invalid values
+typeset badvals=("off" "on" "1" "nope" "-")
+for badval in ${badvals[@]}
+do
+	log_mustnot zfs set snapdev="$badval" $ZVOL
+done
+
+# 2. Verify "snapdev" adds and removes device nodes when updated
+# 2.1 First create a snapshot then change snapdev property
+log_must zfs snapshot $SNAP
+log_must zfs set snapdev=visible $ZVOL
+block_device_wait
+blockdev_exists $SNAPDEV
+log_must zfs set snapdev=hidden $ZVOL
+block_device_wait
+check_missing $SNAPDEV
+log_must zfs destroy $SNAP
+# 2.2 First set snapdev property then create a snapshot
+log_must zfs set snapdev=visible $ZVOL
+log_must zfs snapshot $SNAP
+block_device_wait
+blockdev_exists $SNAPDEV
+log_must zfs destroy $SNAP
+block_device_wait
+check_missing $SNAPDEV
+
+# 3. Verify "snapdev" is inherited correctly
+# 3.1 Check snapdev=visible case
+log_must zfs snapshot $SNAP
+log_must zfs inherit snapdev $ZVOL
+log_must zfs set snapdev=visible $TESTPOOL
+verify_inherited 'snapdev' 'visible' $ZVOL $TESTPOOL
+block_device_wait
+blockdev_exists $SNAPDEV
+# 3.2 Check snapdev=hidden case
+log_must zfs set snapdev=hidden $TESTPOOL
+verify_inherited 'snapdev' 'hidden' $ZVOL $TESTPOOL
+block_device_wait
+check_missing $SNAPDEV
+# 3.3 Check inheritance on multiple levels
+log_must zfs snapshot $SUBSNAP
+log_must zfs inherit snapdev $SUBZVOL
+log_must zfs set snapdev=hidden $VOLFS
+log_must zfs set snapdev=visible $TESTPOOL
+verify_inherited 'snapdev' 'hidden' $SUBZVOL $VOLFS
+block_device_wait
+check_missing $SUBSNAPDEV
+blockdev_exists $SNAPDEV
+
+log_pass "ZFS volume property 'snapdev' works as expected"