growfs_fstab: add new /etc/rc.d script to add swap to fstab

The growfs_fstab script is a helper for the growfs script to add any
new swap partition to /etc/fstab on first boot.  If growfs adds a
swap partition, it sets growfs_swap_pdev in the kenv.   In this case,
after the root file system is read/write, if there is no swap partition
in the fstab, growfs_fstab adds growfs_swap as a swap partition to the
fstab.  Also, it runs dumpon to add the swap partition  (as this
happened earlier in the startup sequence).

Discussed with:	cperciva
Differential Revision:	https://reviews.freebsd.org/D37463

libexec/rc/rc.d/growfs_fstab

@@ -0,0 +1,67 @@
+#!/bin/sh
+#
+# Copyright 2022 Michael J. Karels
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+# $FreeBSD$
+#
+
+# PROVIDE: growfs_fstab
+# REQUIRE: growfs root
+# KEYWORD: firstboot
+
+# If the growfs script added a swap partition, then add a swap entry
+# to /etc/fstab if none exists, and add as dumpdev.
+
+. /etc/rc.subr
+
+name="growfs_fstab"
+desc="Add new swap partition to /etc/fstab"
+start_cmd="growfs_fstab_start"
+stop_cmd=":"
+rcvar="growfs_enable"
+
+growfs_fstab_start()
+{
+	if kenv -q growfs_swap_pdev >/dev/null
+	then
+		if awk '
+			/^#/ { next }
+			$3 == "swap" { exit 1 }
+		    ' < /etc/fstab
+		then
+			printf "/dev/label/growfs_swap\tnone\t\tswap\tsw\t\t0\t0\n" >>/etc/fstab
+
+			case "$dumpdev" in
+			[Aa][Uu][Tt][Oo])
+				dumpon $dumpon_flags /dev/label/growfs_swap
+				;;
+			*)
+				;;
+			esac
+		fi
+	fi
+}
+
+load_rc_config $name
+run_rc_command "$1"