rc(8): Add a zpoolupgrade rc.d script

If a zpool is created by makefs(8), its version is 5000, i.e., all
feature flags are off.  Introduce an rc script to run `zpool upgrade`
over the assigned zpools on the first boot.  This is useful to the
ZFS based VM images built from release(7).

Reviewed by:	imp, markj, mav
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D37282

libexec/rc/rc.conf

@@ -77,6 +77,8 @@ zfskeys_enable="NO"	# Set YES to autoload ZFS encryption keys
 zfs_bootonce_activate="NO" # Set YES to make successful bootonce BE permanent
 zpool_reguid=""		# Set to zpools for which the GUID should be replaced
 			# upon first boot.
+zpool_upgrade=""	# Set to zpools for which the version should be upgraded
+			# upon first boot.
 
 # ZFSD support
 zfsd_enable="NO"	# Set to YES to automatically start the ZFS fault

libexec/rc/rc.d/Makefile

@@ -328,6 +328,7 @@ ZFS+=		zfsd
 ZFS+=		zfskeys
 ZFS+=		zpool
 ZFS+=		zpoolreguid
+ZFS+=		zpoolupgrade
 ZFS+=		zvol
 ZFSPACKAGE=	rc
 .endif

libexec/rc/rc.d/zpoolupgrade

@@ -0,0 +1,25 @@
+#!/bin/sh
+
+# PROVIDE: zpoolupgrade
+# REQUIRE: zpool
+# BEFORE: mountcritlocal
+# KEYWORD: firstboot nojail
+
+. /etc/rc.subr
+
+name="zpoolupgrade"
+desc="Upgrade zpool version"
+rcvar="zfs_enable"
+start_cmd="zpoolupgrade_start"
+
+zpoolupgrade_start()
+{
+	local pool
+
+	for pool in ${zpool_upgrade}; do
+		zpool upgrade $pool
+	done
+}
+
+load_rc_config $name
+run_rc_command "$1"

share/man/man5/rc.conf.5

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd August 28, 2022
+.Dd November 7, 2022
 .Dt RC.CONF 5
 .Os
 .Sh NAME
@@ -2109,6 +2109,13 @@ A space-separated list of ZFS pool names for which new pool GUIDs should be
 assigned upon first boot.
 This is useful when using a ZFS pool copied from a template, such as a virtual
 machine image.
+.It Va zpool_upgrade
+.Pq Vt str
+A space-separated list of ZFS pool names for which version should be upgraded
+upon first boot.
+This is useful when using a ZFS pool generated by
+.Xr makefs 8
+utility.
 .It Va gptboot_enable
 .Pq Vt bool
 If set to