As of r364746 (OpenZFS import) existing ZPOOLs are not imported

prior to zvol and mountcritlocal resulting in ZVOLs (swap and
virtual machine UFS filesystems) being unavailable, leading to
boot failures.

We move the zpool import from zfs to a new zpool script, with the
-N option to avoid mounting datasets while making the ZPOOL's
datasets available for "legacy" mount (mountpoint=legacy) and ZVOLs
available for subsequent use for swap (in the zvol rc sript) or
for UFS or other filesystems in fstab(5), mounted by mountcritlocal.

Reviewed by:		freqlabs (previous version)
Differential Revision:	https://reviews.freebsd.org/D26185

libexec/rc/rc.d/Makefile

@@ -318,6 +318,7 @@ CONFGROUPS+=	ZFS
 ZFS+=		zfs
 ZFS+=		zfsbe
 ZFS+=		zfsd
+ZFS+=		zpool
 ZFS+=		zvol
 .endif
 

libexec/rc/rc.d/mountcritlocal

@@ -4,7 +4,7 @@
 #
 
 # PROVIDE: mountcritlocal
-# REQUIRE: root hostid_save mdconfig
+# REQUIRE: root hostid_save mdconfig zvol
 # KEYWORD: nojail shutdown
 
 . /etc/rc.subr

libexec/rc/rc.d/zfs

@@ -25,13 +25,6 @@ zfs_start_jail()
 
 zfs_start_main()
 {
-	local cachefile
-
-	for cachefile in /boot/zfs/zpool.cache /etc/zfs/zpool.cache; do
-		if [ -r $cachefile ]; then
-			zpool import -c $cachefile -a
-		fi
-	done
 	zfs mount -va
 	zfs share -a
 	if [ ! -r /etc/zfs/exports ]; then

libexec/rc/rc.d/zpool

@@ -0,0 +1,31 @@
+#!/bin/sh
+#
+# $FreeBSD$
+#
+
+# PROVIDE: zpool
+# REQUIRE: hostid
+# BEFORE: zvol mountcritlocal
+# KEYWORD: nojail
+
+. /etc/rc.subr
+
+name="zpool"
+desc="Import ZPOOLs"
+rcvar="zfs_enable"
+start_cmd="zpool_start"
+required_modules="zfs"
+
+zpool_start()
+{
+	local cachefile
+
+	for cachefile in /boot/zfs/zpool.cache /etc/zfs/zpool.cache; do
+		if [ -r $cachefile ]; then
+			zpool import -c $cachefile -a -N
+		fi
+	done
+}
+
+load_rc_config $name
+run_rc_command "$1"

libexec/rc/rc.d/zvol

@@ -4,7 +4,7 @@
 #
 
 # PROVIDE: zvol
-# REQUIRE: hostid
+# REQUIRE: zpool
 # BEFORE: dumpon
 # KEYWORD: nojail